| Author | Message | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 643 Registered: 1-2003 Posted From: 67.142.130.36 Rating: |
OK, I have another question for the team: After arriving in Santa Fe Monday, I noticed a loss of power. Subjectively, it felt like a fuel delivery issue, and subsequent inspection confirmed this. I have a Davco Fuel Pro 380 (superseded by the similar 382, if you want to have a look at one on Davco's web site at http://www.DavcoTec.com). This combination water separator/fuel filter has a clear bowl with a visible cartridge filter media in it. The way it is supposed to work (and has done flawlessly up to this point) is that the fuel level, visible in the bowl, starts out at about an inch up from the bottom. Over time, as the filter media becomes plugged, the fuel level rises in the bowl, until it reaches the top of the media, which is when you are supposed to change the cartridge. My media was less than half used when I left PEDCO, with the fuel level in the bowl being at about the 40% mark. It remained there on several inspections over several days. When I noticed the loss of power here in Santa Fe, the fuel level in the bowl had, mysteriously, dropped below the level of the retaining collar. Davco technical bulletin 3097 advises that these symptoms indicate a missing grommet below the filter, or a broken spring above it. So, today, I replaced the cartridge, grommet, and both O-rings, and inspected the spring. All should now be normal, although the spring may be a bit weak from age. Filling the bowl with fresh fuel relieved the power complaint. But in just five miles of driving, the power again dropped, and, upon inspection, the fuel level is, once again, below the collar. So here are my questions: (1) Is it possible to have a fuel pump that's *too* strong? For example, could the wrong fuel pump have been installed during the rebuild? I ask this because a pump generating too much vacuum could be drawing the fuel out of the bowl faster than it can be replaced. But, also, immediately after the rebuild, we had a problem with the 10psi Kysor fuel pressure switch sutting off the starter circuit before the engine was finished cranking. That switch is now out of the circuit (I am still looking for a replacement), but, perhaps the switch is fine, and fuel pressure is simply building to 10psi sooner than expected -- another possible sign of a hyperactive fuel pump. I've never heard of this, but I thought I'd ask. (2) The more likely explanation for this is that the fuel supply line is restricted somewhere upstream of the Davco. (Interestingly, this also happened the last time we had the engine rebuilt at PEDCO, and they replaced the main fuel line from the tank to the Davco.) Since all was normal for ~800 miles after the in-frame, and this problem developed fairly suddenly, my immediate thought was collapsed hose, but these are double-steel-braid hoses. So what diagnostic tips and tricks can you offer to help diagnose a main fuel line restriction? (3) The only other explanation I can come up with for the symptoms is that the Davco unit is leaking someplace, allowing air into the bowl. I've double-checked the assembly visually, but see nothing obvious. So, can you think of a way to determine if it is possibility #2 or #3 without pressure-testing the Fuel Pro? Any and all suggestions welcome. -Sean http://OurOdyssey.BlogSpot.com | ||
| David Evans (Dmd)
Registered Member Username: Dmd Post Number: 183 Registered: 10-2004 Posted From: 72.80.31.30 Rating: N/A |
Check the end of your pickup tube if you can. Ours had goo on the screen once with low power problem.Maybe you could by pass the fuel pro assy and to rule out the tank to filter lines hook up a temp gal fuel tank (outboard tank) | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 704 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
If you are getting air sucked into the filter, you should see bubbles or a little foam.I take it that someone removed the origional primary and secondary fuel filters? You did check this? Because an out of sight primary filter might be getting time to replace. Possible that one of the fuel lines is pinched or kinked somewhere. Chunk of dirt in pickup line at tank. Has the tank ever been cleaned or checked for dirt, esp at the pickup in the tank? Have you put a pressure gage on fuel line coming from fuel pump to engine? Usually fuel line goes into end of cylinder head to internal fuel passage. Will probably need to tee temporary into this line.Fuel pressure with engine operating against the governor- 21 to 2400- should be 50 to 70 psi. Pump suction should be 6 in. of mercury with new filter,s or 12 with dirty. You can check fuel pressure with an oil pressure gage, but if it can be threaded into fuel port in head, should use an oil filled one, as vibration from engine can damage reg gage in short order. This is why remote oil gages are up on bulkhead. You can rig up a short piece of hose and adapter to accomplish this also. This is done with trans in neutral, parking brakes set, and with gage attached without leaks or near any moving parts, have someone run the engine up against the governed speed for no more than, say ten seconds while you hold the gage and note the reading. If you can do this all from engine compartment, it is easier for communication. Use ear plugs, as the noise running at full governed speed is quite loud and can mess up your concentration on what you are doing OR have a diesel tech do this if it isn't something you are comfortable doing yourself. After checking this, remove gage and restore fuel line back the way it was before you started. | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 72 Registered: 1-2007 Posted From: 65.61.96.82 Rating: N/A |
Sean, First thing I would try is blowing air back through the fuel line to the tank to clear anything that might be plugging the line or intake. Costs nothing. Since I believe you said you still had the original filters in place, I would bypass the Davco to eliminate that possibility. I would start with another fresh set of filters. I would do these one at a time to know for sure which has an effect if any. I know, a pain, but the only way to isolate it. You may also have a leak in the supply line. If Pedco installed a new line with any hose that is clamped, the clamps or fittings may need tightened. Would also check for any possible rubbed places. Check the line before you blow it out and again after to see if it 'sweats' any diesel. A sure sign of an air leak. As mentioned above installing a fuel pressure gauge would tell you a lot too. Good luck Don 4107 | ||
| Ed Roelle (Ed_roelle)
Registered Member Username: Ed_roelle Post Number: 29 Registered: 3-2005 Posted From: 68.85.142.109 Rating: N/A |
What material did Pedco use when they replaced your fuel line? If rubber, you may be having a collapsed hose from the tank to the filter. I have not heard anything discussed about rubber hose with diesel fuel. To most people, it doesn't matter. Possibly, most fuels do not effect the rubber. But, the chemical properties of diesel fuel, are such that there is a specific hose specification for diesel fuel, as I remember. Can you run a temporary fuel hose on the side of the bus from the tank to the filter? Ed Roelle Fint, MI | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 426 Registered: 11-2005 Posted From: 63.97.117.55 Rating: N/A |
Sean, If your fuel basically is like a GMC it is suction to the primary filter and fuel pump and pressure to the secondary and injectors. If your Davco filter is getting air either directly or through the primary filter and pump that would account for the low fuel level and good performance after you fill it. The same thing happened to my 4104 and I had a very small air leak at the primary filter (Suction side). The frustrating part of suction side leaks is there is no fuel leaking because air is entering, nothing is leaking out. This post is with my not being familiar with your fuel system or Davco filters. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 644 Registered: 1-2003 Posted From: 67.142.130.15 Rating: N/A |
I should clarify my installation details: The Davco Fuel Pro normally replaces both primary and secondary filters. This is an approved configuration per Detroit. The filtration media in the Fuel Pro filters to the same micron rating as the secondary. So my primary filter, its mount, and the threaded stud for it are long gone. Normally, because the plumbing on the secondary is more complex (one input, two outputs), the secondary mounting and threaded stud are left in place, and Davco supplies a "dummy" filter housing (looks like a filter, but only an inch or so long) that threads onto the secondary mount. I elected not to use the dummy, and have a real secondary filter (Baldwin 5810) installed. The lift pump is between the Davco and the secondary, just as it normally would be between the primary and secondary. This means that the Davco is under vacuum in operation, with the lift pump "sucking" fuel out of the Davco, and the resulting vacuum in the Davco in turn sucking fuel out of the tank through the main supply hose. By design, there is a certain amount of air and fuel vapor in the Fuel Pro, and, as the media plugs, that vapor is slowly ingested by the lift pump and pumped through the secondary and into the rails. A check valve just before the Fuel Pro keeps fuel from draining back to the tank through the supply line, even if the Fuel Pro is open to atmosphere (such as when the filter media is changed). The fuel line PEDCO installed two years ago is double braided stainless -- it's really hard to collapse this stuff. And there is no visible damage. If there was an air leak in the main supply line, ahead of the check valve, I would lose prime, as that fuel would eventually drain back into the tank as the line filled with air. So I have either a restriction in the main supply (plugged line, clogged tank pickup, bad check valve), an air leak downstream of the check valve (such as a hairline crack in the bowl, or bad O-ring), or enough leakage between the media cartridge and the intake grommet for the fuel to be bypassing the media. Tomorrow I will take the thing apart again and double-check for cracks or bad O-rings. The suggestion to blow some air back through the main supply line is a good one, however, I will need to (1) go buy myself some fittings to adapt an air hose to the fuel line and (2) figure out a way to re-prime the main supply line once I'm done. (I don't have a priming pump.) Any suggestions on this latter question? -Sean http://OurOdyssey.BlogSpot.com | ||
| Ed Roelle (Ed_roelle)
Registered Member Username: Ed_roelle Post Number: 30 Registered: 3-2005 Posted From: 68.85.142.109 Rating: N/A |
First on repriming. Can't you fill the Davco / crank /fill Davco ... until engine starts. Second. Sorry I missed your earlier information about fuel line material. You may have a more unusual problem. Thus, don't rule-out a collapsed hose. There is a liner in the braided stainless. Although rare, there have been occurances of hydraulic brake hose (which is highly regulated and with multiple material layers), to have a collapsed inner liner. Third. I haven't put this all together, only a common symptom and a long shot. We were working on a Kubota diesel generator 2 weeks ago. The prime was excellent but it would not start. However, the fuel in the filter was going DOWN. Later, we found that there was no fuel going to the injectors. For some reason, could you be limiting fuel flow in the injector system? Lean mix, low power, overheat ...? Ed Roelle Flint, MI | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 646 Registered: 1-2003 Posted From: 67.142.130.43 Rating: N/A |
Ed, Yes, I can prime that way. In my head, I was trying to think about how to do this if I bypass the Davco, which is one of the things I am thinking about. I can't imagine that this problem could be downstream of the lift pump. Nothing that happens in the injectors or on the rails would be causing the lift pump to suck all the fuel out of the Davco. Besides, once I fill the Davco up with fresh fuel, all the problems go away, at least until it empties again. -Sean http://OurOdyssey.BlogSpot.com | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 708 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Unhook the fuel return line and run it into a jar while submersed in fuel. Run engine and look for bubbles after air is purged from line. Do bubbles come out of line? | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 474 Registered: 7-2006 Posted From: 66.217.102.145 Rating: N/A |
Re: "once I fill the Davco up with fresh fuel, all the problems go away, at least until it empties again." That can also be interpreted as: In the time it takes to fill the Davco, the engine cools. The cooled engine is started, running, and heating up. As the engine heats up, the Davco empties. (Is something heating up with the engine, causing the fuel problem?) (By the way, the fan clutch spring (or lockup) could be on the radiator side, and tough to see without removing the radiator, or using a mirror..) (Message edited by john_mc9 on August 09, 2007) | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 428 Registered: 11-2005 Posted From: 63.97.117.48 Rating: N/A |
Sean, If you blow out the supply line be sure to open the filler cap. The problem with this is that then you will somehow have to recharge the supply line with fuel. No reason you can't do it from the engine end, which should be a lot easier. | ||
| Hans (Buellhans)
Registered Member Username: Buellhans Post Number: 73 Registered: 2-2007 Posted From: 199.60.189.9 Rating: N/A |
Sean why dont you just junk your bus seems to have a lot of problems | ||
| Bruce Henderson (Oonrahnjay)
Registered Member Username: Oonrahnjay Post Number: 154 Registered: 8-2004 Posted From: 12.77.65.254 Rating: N/A |
__. Are there any commonly-available N American buses that have a one-way (or anti-drainback) valve at the tank? I ask because obviously such a valve would prevent using an air line to blow out clogs backward toward the tank. __. I'm much more familiar with British buses - and many of those in N America are now quite old. One of the best things that you can do for them is to put a small "lift pump" at the tank. Rather than a pinhole leak causing your filters to drain and stopping your bus, you have a site where you can see drops of fuel and repair the line at that point -- with the obvious differenc that your bus doesn't lose prime and stop on the side of the road. Of course, it takes a lot of strain off the pump in your injection system and has an added side effect of assuring full fuel flow, rather than a mixture of fuel and air. It stops problems other than pinholes (loose filter cups, etc.) that might lose prime, plus if you have to service your system, you can quickly and easily reprime. __. I believe that a low-pressure, high-flow 12-volt pump can be bought for $35-45 (US) and designs are available with a flow-through so if the lift pump quits working for any reason, the engine pump can still draw fuel through it normally. If the pump that I wanted to use didn't have a flow-through, I'd add a separate one-way bypass valve. __. Having a lift pump also allows you to install a fuel pressure gauge just after the tank. This will show you an empty tank, a bent or clogged fuel pickup, etc at startup -- if you're seeing good fuel pressure even before you start, you know that you're seeing good fuel supply from the tank. A situation like dry filters or fuel starvation after the filters would indicate clogged or dirty filters or a clog somewhere between the gauge and the filters. This simplifies the troubleshooting of the entire fuel system, and a gauge would also give you a quick pre-start check that the lift pump is working properly. __. Again, this might not be useful on all N American built buses (or indeed any N American buses), but it sure is a big help in increasing the reliability of buses that I'm familiar with. __. And it seems to me that if Sean had a positive flow of fuel from the tank through his high-tech filters, he'd have much less problem tracing down the problem that he has. Am I wrong on this? | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 647 Registered: 1-2003 Posted From: 67.142.130.42 Rating: N/A |
Re: Check valves. I have to be honest, I don't know if there are any check valves in the supply line other than the one on the input side of the Fuel Pro. I don't see anything that looks like a check valve at the egress from the tank, which I would think is the most likely place. Re: Electric fuel pump at the tank. This would make me very nervous. First off, a Detroit needs a massive flow of fuel (my fuel line is nearly a half inch ID), so you are talking about a big pump. And now, if you do puncture or burst a fuel line, instead of just drawing a vacuum and having the engine quit, you now have fuel potentially spraying all over a hot engine compartment -- a recipe for disaster. I'll take the headache I have now (hard-to-diagnose fuel delivery problem) over the possibility of fire on the road, thanks. Just my opinion, of course. I'll be road-testing the coach in just a few minutes, after having cleaned and reassembled the Davco yesterday, and we'll see if that takes care of the problem. If not, I've also got the parts now to hit the main supply with a shot of air. -Sean http://OurOdyssey.BlogSpot.com | ||
| Sammy (Sammy)
Registered Member Username: Sammy Post Number: 72 Registered: 8-2005 Posted From: 68.237.226.130 Rating: N/A |
Sean, most buses with 2 strokes have the single check valve mounted on the engine bulkhead. The primary fuel line (suction) coming from the fuel tank will secure to this check valve (most times it's on the fuel tank side of bulkhead), pass thru a bulkhead connector, to another primary (suction) line, then to a primary fuel filter(in your case your FuelPro), then to suction side of fuel pump.You will NOT be able to blow air back to the tank if your bus has one in the location I mentioned. | ||
| JJ Woden (Jj_woden)
Registered Member Username: Jj_woden Post Number: 33 Registered: 10-2006 Posted From: 65.19.246.49 Rating: N/A |
Sean, and others, if you locate the check valve, you can hook an electric fuel pump in parallel with the fuel line. Merely tee the pump inlet to the tank side of the check valve, and the pump outlet to the engine side of the check valve. The electric pump can then be used to prime the system, fill new fuel filters, pressurize the system for testing, and, in a pinch, supply the engine with barely enough fuel to limp it to a suitable parking spot for repairs. The pump in this location will not interfer with normal operation of engine or fuel flow. And the two check valves will prevent back flow. There are a number of ways to prevent the pump running when there is an engine shutdown: Oil pressure switch, sense alternator output, time delay and/or relay, depending on the need. JJ Woden | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 432 Registered: 11-2005 Posted From: 63.97.117.33 Rating: N/A |
My 4104 supply line check valve is on the engine side of the firewall at the input to the primary filter. A logical location which I would hope most buses use. Sure makes access easy. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 712 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Burst a double braided fuel line? what kind of electric fuel pump did you envision that he suggested? You need to take that Davco off, get a pair of normal screw on filter units and end this this nightmare. With screw on filters, you only have the oring seal at each filter to cause leaks, which is part of filter and gets replaced at every filter change, plus ,elements are cheap; no internal orings, no springs to weaken, no housing or clear fuel bowl warpage or leakage, which i've seen happen on the smaller automotive versions. Luke could get you a takeoff filter pair, or you can get them from Napa or any larger parts store- listed in back of master filter catalog. Filter changes are easy for the rest of us. Unscrew old one, fill new one with fuel, and screw back on, start engine and idle for a few minutes, and then go on down the road. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 649 Registered: 1-2003 Posted From: 67.142.130.20 Rating: N/A |
John, I love my Fuel Pro, and I'm not inclined to ditch it without good reason. Also, no one has offered a credible theory that says the Fuel Pro is at fault here. More likely, the clear bowl of the Davco is giving me more insight into a problem that a regular spin-on filter would still have me scratching my head over. The filter O-ring is also not the only potential source of trouble in even a conventional two-spin-on setup. There are several, if not dozens of, fittings in the fuel supply system. The secondary filter alone has nine fittings and three hoses associated with it, and the primary filter has at least four fittings and two hoses, not to mention check valves, etc.. Any one of those places can be a source of air intrusion, fuel leakage, or clogging. In normal operation, none of those fittings is messed with, and they are unlikely (but not impossible) sources of trouble. But I just had my engine rebuilt, and, believe me, every hose, fitting, and filter mount was removed and reinstalled, and it is just as likely I would be having a problem with a conventional primary filter as with this Fuel Pro. To be more succinct, without the Fuel Pro and it's visibility, the minute I experienced this low power problem I would have been thinking along the lines of engine rebuild issues, like a bad turbo, or a rag left in the intake. The Davco told me right away that I have a fuel supply problem, and, with conventional spin-ons, it might have been quite a bit longer before I came to that realization. At this moment, I am fairly certain I have either an air leak or a restriction upstream of the Fuel Pro. I'll find it, somehow. The Fuel Pro will probably help me with this troubleshooting. BTW, I can turn that Fuel Pro right back into a conventional primary just by removing the bowl and spinning on a standard primary filter in its place. I carry one of these for emergencies, in case the bowl cracks, the vent cap comes off, or the retaining ring breaks. Regarding the burst fuel line, I wasn't suggesting that an electric fuel pump alone would do that. But lines do get cut through or abraded -- and several people here have already suggested the line could be leaking. If that line was under pressure, the leak would be raw fuel in a hot engine bay -- I stand by my safety concerns with this. -Sean http://OurOdyssey.BlogSpot.com (Message edited by sean on August 11, 2007) | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 476 Registered: 7-2006 Posted From: 68.205.165.5 Rating: N/A |
I'm gonna' stick my neck out here (again), Sean.... I think what John's saying is, that by bypassing the Davco, you'll be taking one more thing out of the equation. You're going to have to shoot this trouble by the process of elimination, and bypassing certain items, may be your only recourse. It's the easiest, most cost effective, and most visual way to go about it. It's like locking up a fan clutch, rather than replacing it..... Bypassing anything temporarily that "might" be a problem, isn't all that bad an idea. You can speculate forever, and ask as many questions you desire from the Peanut Gallery, but a garage is going to do exactly what anyone else is telling you has to be done: Use the process of elimination to isolate the problem. After a major rebuild, costing what you've paid? I'd been back in their yard two weeks ago..... | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 650 Registered: 1-2003 Posted From: 67.142.130.20 Rating: N/A |
John, I did not read that as "bypass for troubleshooting." I read it as "get rid of, and replace with standard spin-on primary." If I misunderstood, mea culpa. Of course bypassing the Davco (temporarily) is one of the troubleshooting steps. I said so myself (but I am not there yet in the process). It's not something I can do here, because I don't then have a way to prime the system to get the engine running. -Sean http://OurOdyssey.BlogSpot.com | ||
| Ed Roelle (Ed_roelle)
Registered Member Username: Ed_roelle Post Number: 31 Registered: 3-2005 Posted From: 68.85.142.109 Rating: N/A |
A fellow I know uses an inexpensive garden sprayer filled with diesel fuel, to prime his system. We used it successfully also. Have you confirmed that you have a check valve between your tank and Davco? I think MCIs check valve is in the return line to the tank (at the engine), not in the supply. Ed Roelle Flint, MI | ||
| Muddog16 (Muddog16)
Registered Member Username: Muddog16 Post Number: 359 Registered: 11-2004 Posted From: 4.224.243.229 Rating: N/A |
Sean, I tried to post this on here but the file was to large and when I tried to reduce the file size you couldn't even see the picture or parts list. This is a circuit for primming diesel. It's on my site the very top picture, if you click on the photo you can see all of the photo and parts list. When you mentioned that you couldn't prime your system this sure would come in handy! I can't remember where or who made this drawing but it sure is niffty! Just a thought.....good luck! Pat http://prevostlemirage.blogspot.com/ | ||
| Muddog16 (Muddog16)
Registered Member Username: Muddog16 Post Number: 360 Registered: 11-2004 Posted From: 4.224.243.229 Rating: N/A |
Sean, I tried to post this on here but the file was to large and when I tried to reduce the file size you couldn't even see the picture or parts list. This is a circuit for primming diesel. It's on my site the very top picture, if you click on the photo you can see all of the photo and parts list. When you mentioned that you couldn't prime your system this sure would come in handy! I can't remember where or who made this drawing but it sure is niffty! Just a thought.....good luck! Pat http://prevostlemirage.blogspot.com/ | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 131 Registered: 12-2000 Posted From: 75.89.31.142 Rating: N/A |
Muddog, That's the same thing I have done on my 4104, saves a lot of aggravation. You can save a few dollars by substituting a ball valve for the check valve and operating it manually (as I have on mine)  | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 715 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
Whatever, but just my opinion. Anyway from the troubleshooting section of the Detroit Diesel manual: Disconnect the fuel return line from the fitting at the fuel tank, or at engine bulkhead if you cant get to the tank...and hold open in a convenient receptacle. For turbocharged engines with a restriction fitting of .070 spill orfice, start and run engine at 1800rpm and measure fuel flow for a period of one minute. A flow of 1.4 gallons per minute is specified. Immerse the end of the fuel line in the container. Air bubbles rising to the surface of the fuel will indicate air being drawn into the fuel system on the suction side of the pump. If air is present, tighten all fuel line connections between fuel tank and pump, OR THROW AWAY DAVCO!!- just kidding. Also check engine fuel pump because it has an excess pressure by pass, which if stuck somewhat open from a little dirt, could lower fuel pressure and volume. This it why I suggested the pressure and volume tests and also the bubble tests. The questions about the radiators, outside temps and how much you used it before, etc. were in an attempt to get all the details, which maybe stated before, but I may have overlooked. Radiators do get solder bloom at the ends of the tubes over time which can decrease cooling ability gradually over time. As far as the fuel level going down, it could be as simple as a primary filter starting to plug up but not enough yet to cause total starvation, but COULD or MIGHT increase the tendendacy to try to suck air from somewhere that might not allow air into the system otherwise. Maybe you already replaced the primary filter, but after 50+ posts, I'm getting tired from all the reading and maybe missed it.Do some of the basic diagnostic procedures above, then we can narrow down whether it is air or fuel starvation.This is posted to be helpful to your problem, not to flame. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 652 Registered: 1-2003 Posted From: 67.142.130.36 Rating: N/A |
Thanks, John. I'm less cranky now (but only slightly -- I've been fighting with fuel fittings all day in full sun). Today's project was removing all the fuel fittings between the primary and the supply line. Of course, I didn't have the right wrenches, and even Sears didn't have 1-3/4". They did have the 1-1/4" and 1-1/16" (really) open-ends that I needed. At least one of the fittings, a 1/2" NPT brass street ell, was bottomed out and not making a tight seal. Even getting to that was a challenge -- the main supply was tightened down by a gorilla (actually, mechanic Vicente, who probably weighs 330), and to even get it loose, I had to oppose two wrenches, and use a turnbuckle as a come-along to bring them together. Anyway, I completely cleaned out the threads on all the fittings I needed to reuse, replaced the bad street ell, and once again cleaned and replaced all the O-rings. She ran fine for 20 minutes at high idle, running about 13% engine load. In that time, the fuel level in the Fuel Pro dropped about 1/4", which I think corresponds to the whole thing heating up and the air/vapor above the fuel expanding somewhat. I won't know if I've fixed the problem until I actually get it out on the road, probably Monday. If the problem is still with me, I need figure out how I'm going to get to the tank fittings (really, really hard on my bus) to look for leaks or obstructions there. I'm now pretty sure there must be another check valve, since the amount of air I got when I fired it up corresponded only to the couple feet of fuel line that I emptied when I disconnected it, not the whole 20' or so back to the tank. So blowing air through the line is not an option. The whole cooling system issue is on hold until I fix this fuel delivery problem. As a complete side note, but some following the discussion may find it interesting: I have the older Davco FuelPro 380E. This thing is a monster compared to the newer 382, with an aluminum housing that must be 15" tall. Since I had to empty it all the way down to the check valve today (which I then removed, cleaned, inspected, and reinstalled), I drained it the whole way so I could replace the drain valve at the bottom. Actually, what I needed to do was put a street ell ahead of the drain valve, which otherwise opened up basically right above the crankshaft pulley -- really inconvenient when draining the water out, or enough fuel to remove the bowl. Dang! That thing holds nearly a gallon of fuel! That's in addition to the amount above the collar, that you can see in the bowl. I only have a 1.1 gallon jerry can, so I was just barely able to get enough fuel back into the unit to prime the system without having to run out on the scooter for more diesel. What I also learned, when I had all the fittings off the unit and could swipe my fingers around inside, is that it is mostly empty. I think most of the space at the bottom is for hydronic coils, which was a pre-heat option on these units. Anyway,the 382 is much smaller, and I confess now to some Fuel Pro envy. -Sean http://OurOdyssey.BlogSpot.com | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 480 Registered: 7-2006 Posted From: 66.217.107.150 Rating: N/A |
"I confess now to some Fuel Pro envy. " More like a fetish.... ;>) | ||
| Christopher Goodwin (Cgoodwin)
Registered Member Username: Cgoodwin Post Number: 112 Registered: 10-2005 Posted From: 71.212.78.253 Rating: N/A |
Sean, I posted this once before but it fell on deaf ears. I sold the Davco 234 for several years, I have worked with several hundred on vehicles and I can tell you that there are some design issues with Davco filters which led me to drop them entirely, every one has produced the results you are having and are casued by air leaks. In order for the "seeing is believing" part of the unit to work it must be installed in vacuum fuel systems. As the filter media plugs the level of fuel in the "Dome" climbs up the filter and you can see that the filter is clogging - this could also be more easily accomplished with a Hobbs switch on the outlet side of any filter connected to an indicator on the dash. The filter bodies have at least 5 points of failure, the most common I have seen are the gasket on the bowl where the collar tightens it to the body - this collar cracks or strips and leaks air, the edge of the bowl gets a gouge in it from not being properly aligned and leaks or the o-ring fails. The same faults occure at the prime plug on top. I have seen the balls in the check valve and the spring go into the filter and the ball clogs the inlet because the cage holding the spring and ball is plastic and cracks at the clip where it joins the fitting and starves the vehicle for fuel, this will also increase system vacuum and exasberate any leaks. At the end of the day the Fuel Pro does nothing whihc can not be more easily accomplished with less points of failure and this alone should set you thinking. A large spin on filter like the one originally fitted to your engine, fitted with a "T" at the outlet and a Hobbs switch connected to a light or an electric sender to a vacuum gauge on the dash would allow you to know the condition of the filter BEFORE it was an issue, to do so from the control panel while driving and to replace the filter inexpensively at any truck stop. Put a check valve on the filter inlet (there was one on your original filter, I promise) to allow filter changes without difficult starts and you have done more than the fuel pro ever could and lessened the points of failure. Diesel injectors abhor air, they are designed to compress and deliver fuel, they have no seals and rely on the viscosity of the fuel to form a seal, if you introduce air they simply do not deliver fuel, like trying to sqiurt air with a squirt gun - it needs the water to form a seal. In addition you have a very good gear pump on the engine, this too is designed to be lubricated by the fuel, if you deliver fuel and air to it the gears will gauld and the pump will fail. It can pump sewage up hill but it will not pump air long enough to fill a balloon! I have a box of Davco filters I replaced for clients sitting in my shop, all suffered air leaks.... | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 653 Registered: 1-2003 Posted From: 67.142.130.38 Rating: N/A |
Chris, Thanks, that's the most comprehensive critique of this product that I have seen yet. I'm pretty sure my current problem is upstream of the Fuel Pro. However, I am looking for some fittings so that I can bypass it if this turns out not to be the case. From your experience with these, do you think my unit could be ingressing air around the lower bowl seal without any evidence of air bubbles in the bowl? Also, if one of the bowl seals (lower O-ring or vent plug gasket) is the source of the failure, I should be able to work around it, in the short term, by running a spin-on down onto the stud, correct? That will certainly be a quicker and easier thing to try than fiddling around with hose fittings to bypass it. And, if this thing turns out to be leaking, I will likely take your (and John's) advice and go back to a spin-on primary. -Sean http://OurOdyssey.BlogSpot.com | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 193 Registered: 7-2006 Posted From: 4.240.141.132 Rating: N/A |
Good post Chris!! FWIW RCB | ||
| Christopher Goodwin (Cgoodwin)
Registered Member Username: Cgoodwin Post Number: 114 Registered: 10-2005 Posted From: 71.212.78.253 Rating: N/A |
The unit, if similar to the 382 has failure at the base, drain, inlet and outlet fittings as well as the dome collar and the prime port. If the leak is at the prime port or dome collar then a spin on filter will work. I have had so many issues with these that I now simply bypass the filter with a 10 micron barbed filter, if the problem is gone, I know I can blame the Davco, some I have repaired, the others sit in a very expensive pile on my shop floor.... May I recommend the Peterbuilt P174768 remote filter head and the Donaldson 555823 spin on filter, about $60 for the pair with replcement filters at about $10. The ports on the head are #10 ORB and any hydraulics shop will have 10-orb (O-ring boss) which do not leak, you can then install a T and a Hobbs switch ($25) to a light on the dash or a sender to a vacuum gauge. it will provide interesting information and you will begin to notice a serious relationship between fuel temp and system vacuum after the filter, once you establish what is normal and what is plugged for your engine you can choose to install just a light and hobbs switch set to that vacuum. Come on Gadget guy, think about it, a gauge, a light, live data... Or you can stop, leave the engine running under no load and run round back for a peak at the pleasure dome... I went for the Racor FG1000 myself for the VO side and the Donaldson 555823 for the diesel with the gauge...but I am a nut.  Another interesting point here is that we all know when we have plugged fuel filters from bad fuel or a decaying component in the fuel system, we know because we loose power and we loose power because the filter simply plugs up and we loose power. Oil filters ont he otehr hand have a bypass, if the oil is cold and thick or if the filter is plugged, the bypass opens and the oil goes right over the top of the filter and back into the engine. There is no "Filter plugged" light, no indication that the filter is not doing its job at all. I recently maintained a diesel truck motor which had been neglected by the PO, I found that the oil filter was completely filled with what looked like tar as was the oil pan.... (Message edited by cgoodwin on August 12, 2007) (Message edited by cgoodwin on August 12, 2007) | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 438 Registered: 11-2005 Posted From: 63.97.117.15 Rating: N/A |
Chris, These are two of the most educational posts I've seen in a long time. It banishes forever from my mind any thoughts of Davco filters, or any others for that matter. I still have the original stacked disk primary on my 4104 and like it, a bit messy but very effective. The secondary is a spin-on, very easy to change. I had to clean/change them a couple of times when I first got the bus but now there is very seldom any problem, I just clean the primary before any long trip. Sean, I know you're a pretty stubborn guy but admit that Chris has shown the way!! | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1112 Registered: 5-2001 Posted From: 65.74.67.130 Rating: N/A |
Chris, thanks for the informative posts! Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 197 Registered: 7-2006 Posted From: 4.240.144.66 Rating: N/A |
Absolutely....  RCB | ||
| Christopher Goodwin (Cgoodwin)
Registered Member Username: Cgoodwin Post Number: 118 Registered: 10-2005 Posted From: 71.212.52.21 Rating: N/A |
I spend all day designing and building fuel systems and must admit that I too was impressed with the Davco units when they became available, I think I am still listed on their site as a dealer. It took me a while to become disenchanted but with a box full of broken units my wallet reminds me of the foolishness of my eyes. I finally remembered why I found the Davco unit so attractive.... because I grew up with it.  | ||
| Richard Bowyer (Drivingmisslazy)
Registered Member Username: Drivingmisslazy Post Number: 1970 Registered: 1-2001 Posted From: 75.108.83.235 Rating: N/A |
Has anyone heard what has happened to Sean and his fuel and overheating problems? I can not believe he would leave us hanging without telling us the story. LOL Richard | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 445 Registered: 11-2005 Posted From: 63.97.117.31 Rating: N/A |
It may be on MAK, I'm going there next. | ||
| Ron Walker (Prevost82)
Registered Member Username: Prevost82 Post Number: 327 Registered: 11-2003 Posted From: 208.181.210.47 Rating: N/A |
I think they are in the shop getting it checked out Ron | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 658 Registered: 1-2003 Posted From: 67.142.130.43 Rating: N/A |
And the answer is (drum roll, please): Kidney stones. No, seriously -- debris in the fuel return system, at the restrictor orifice. They showed me the debris -- it was smaller than a kidney stone. You could hardly see it. We took the coach in to Stewart & Stevenson in Albuquerque this morning, at the recommendation of Virgil Cooley over at PEDCO. When they tested the fuel pressure, it was around 60PSI at idle, and it should be closer to 25 PSI. So that told them right away where to look. When they pulled the restrictor, they found the debris clogging it. And they were confident that this was the sole reason for both the low power and overheating complaints. And the good news for us -- they didn't even give us a bill. They called PEDCO when they found the trouble, and PEDCO immediately agreed to take care of it. There's no guarantee, of course, that this happened during the in-frame (although the debris was too large to make it through the fuel filters, so it is more likely it got in there while things were open). And this, after all, is one reason we drove 400+ miles to PEDCO when we needed an in-frame -- we trust them, and know they stand behind their work. I have not confirmed this yet, but I suspect the return restriction is also the reason our Kysor fuel pressure switch was cutting out the starter prematurely. I still haven't found a replacement switch, so tomorrow I will put the original one back in and see if it's working now. We had good power coming out of Albuquerque today, and we pulled a couple of good grades without overheating, at much higher speeds and in a higher gear than we were able to a few days ago. So my fingers are crossed that our problems are behind us. That said, the Davco Fuel Pro emptied out again on today's drive, and the coach, subjectively, feels a bit "sluggish" (although definitely not the level of problem we were having in Santa Fe). So the jury is still out on the Fuel Pro issue. I'll put more fuel in it tomorrow and we will monitor the performance moving forward. -Sean http://OurOdyssey.BlogSpot.com | ||
| Ed Roelle (Ed_roelle)
Registered Member Username: Ed_roelle Post Number: 34 Registered: 3-2005 Posted From: 68.85.142.109 Rating: N/A |
Sounds positive at this point. Congratulations. Ed Roelle | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 448 Registered: 11-2005 Posted From: 63.97.117.20 Rating: N/A |
Good news Sean, I can only imagine having this much trouble with my bus. Makes my few problems seem pretty minor. I guess PEDCO didn't find this because the obstruction didn't happen until later. What is the purpose of the restrictor orifice and exactly where is it? I don't remember any mention of such on my 4104. After what Chris said it may be time to bite the bullet on the DAVCO!! | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 660 Registered: 1-2003 Posted From: 72.171.0.148 Rating: N/A |
Gus, I think the obstruction occurred during the rebuild, even before I left PEDCO. That's because, after the road test, and after they checked for leaks and gave me the all-clear, we had cranking trouble, which we traced to the Kysor 10PSI NC fuel pressure switch in the starter circuit. The technician guessed it was just a bad switch -- but, after S&S fixed the obstruction, I put that switch back in, and it's working fine now. So the obstruction happened probably during the road test, and it was causing the fuel pressure at the cut-out switch to rise quickly during cranking. The purpose of the restrictor orifice is to establish a certain fuel pressure at the input side of the injectors. Too big an orifice, and the pressure will be too low, too small and it will be too high. It looks just like an extra fitting on the return side of the fuel system, just after the fuel rail. Dallas did a really good reply to this same question over on the other board, complete with scans of the manual pages for the restrictors, here: http://www.busconversions.com/bbs/index.php?topic=5153.msg48660#msg48660 As far as the Davco, yes, Chris has given me something to think about, but I have no evidence whatsoever that it is having or causing any problems. At this minute, I am pretty convinced that I still also have air entering the system upstream of the Davco. S&S did the bubble-test (putting the return line in a bucket and looking for air bubbles), but they didn't run the Davco all the way out of fuel. So any air coming in upstream of there would be trapped by the Davco and not show up in the bucket. I'm pretty sure now that this is why the fuel supply line was tightened so hard that I needed to make a come-along to loosen it. It's a flare fitting that's, umm, been around the block a few times. I lapped both sides with rubbing compound, then cleaned them up really well before tightening them together, but I suspect they may still be admitting some air. I'm not sure how to test this particular hypothesis, though (suggestions welcome). -Sean http://OurOdyssey.BlogSpot.com | ||
| James Stacy (Jimstacy)
Registered Member Username: Jimstacy Post Number: 92 Registered: 1-2001 Posted From: 75.40.230.92 Rating: N/A |
The restriction is normally in the brass fitting screwed into the fuel rail cast in the head. This is for the fuel return to the tank. This orifice provides a "head" or restriction to flow for the fuel pump. This causes the pressure in the fuel log to be higher and increases the volume of fuel from the injectors. This pressure is often raised by those looking for more HP. For example a spring loaded check valve in the return line rather than the unit that has a loose flap will increase the rail pressure and the HP. My swag? This is not the "root cause" of the problem. Losing fuel level in the Davco unit usually means the pump is sucking air into the filter. A carefull watch of the upper filter while the engine is running, will often show the fine air bubbles (might not always be there) if you're sucking air. A tiny air leak in the suction line, or restriction in the pickup or flow would be my guess for remaining symptoms. I know this has been checked before, but if it were me, I'd replace that suction line, drain the tank to remove debris, pull the fuel pick up tube, etc. There is a problem in there somewhere. BTDT. I've been wrong a time or two in my life, I must admit, but I don't think we've seen all the problem yet. HTH Jim Stacy | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 717 Registered: 10-2003 Posted From: 71.58.117.21 Rating: N/A |
the restriction is in the cylinder head where the fuel return comes out. it is a removeable orfice, and is spec'ed to be a certain thousands in size depending on injector size, turbo or not, horsepower rating etc. Maintains a given pressure and volume at the injectors Blocked fuel return will force a lot more fuel through the injector and mess up spray pattern, causing the above problems. that is why the pressure tests are in the troubleshooting section of the shop manual. It saves hours of guess work on fuel delivery problems. Another words.... IT'S IN DA BOOK!!! At least in the DDA shop manuals. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 661 Registered: 1-2003 Posted From: 72.171.0.148 Rating: N/A |
OK, I've been thinking about this all evening, and now I have another question. First off, I want to reiterate that fixing the clogged orifice has taken care of most of my problem. I've got more power than before, and no overheating. I'm pretty sure, now, that the fuel level dropping in the Fuel Pro is a completely separate issue/problem. I'm now also pretty much convinced that what is happening is that air is entering (very slowly) under load at the main supply fitting. Here's my question. This is a #8 hose (1/2" ID) with a female flare fitting on it. That threads on to a male flare spud. I think I have a bad mating between these. One possibility is that they are incompatible fittings (such as one is 45° SAE and the other is 37° AN). I certainly can't tell by looking -- how would one go about determining if a fitting is SAE or AN? Replacing the fitting (well, at least the female one on the hose) is non-trivial, as the whole supply hose will have to come out. Is there some type of sealant that I could use between the mating faces, not for a permanent solution, but just to prove the hypothesis that this is where the air is coming in? I'm thinking here of, say, a viton O-ring larger than the orifice but smaller than the threads? Or maybe even a smear of petroleum jelly? I think I have pretty much sealed up everything else, at least on the engine end. Since that's the part that was dismantled during the rebuild (as opposed to the tank or bulkhead end), I think it to be the most likely place for the problem to lie. -Sean http://OurOdyssey.BlogSpot.com | ||
| Leland Bradley (Lee_bradley)
Registered Member Username: Lee_bradley Post Number: 20 Registered: 11-2006 Posted From: 138.163.0.44 Rating: N/A |
Sean, I use a light coat of Loctite blue (medium strength) on the male sealing surface, not the threads. Make sure both surfaces are clean. | ||
| Tom Caffrey (Pvcces)
Registered Member Username: Pvcces Post Number: 1115 Registered: 5-2001 Posted From: 65.74.67.130 Rating: N/A |
Sean, stick type pipe thread sealant is widely available, cheap and will take care of flare seal problems. It's very dependable. We've seen many of these situations on the suction line of diesel fired furnaces and boilers. It doesn't take much air in the fuel and they safety out. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher Ketchikan, Alaska | ||
| Christopher Goodwin (Cgoodwin)
Registered Member Username: Cgoodwin Post Number: 122 Registered: 10-2005 Posted From: 71.212.70.132 Rating: N/A |
How is this. take a plastic sandwich bag and cut the bottom open forming a plastic tube. Put it over the line and secure the line to the fitting. Ziptie one end of the plastic tube to the fitting and fill the tube with Vasoline, ziptie the other end around the hose so the juncture is completely immersed in Vasoline. Of course there may be some questions when you and your wife walk out of the store with a box of baggies, a 1/2 gallon of vasoline and a pack of zipties.... Vacuum leaks are a nightmare to diagnose, I build all my systems with JIC fittings and Push-Lok hoses and I have several sections of line with different fittings on the ends and a section of clear polycarbonate tube in the center. I place these in the fuel system at different points before and after components and search for leaks that way. A real PITA. What was the debris made of??? Could it be a piece of fuel line? A piece of the cage of the check valve in the filter? It came from somewhere and I would want to know what it was and where it came from because there may be more... | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 662 Registered: 1-2003 Posted From: 67.142.130.16 Rating: N/A |
"Of course there may be some questions when you and your wife walk out of the store with a box of baggies, a 1/2 gallon of vasoline and a pack of zipties...." You've never been to one of our parties, clearly... "What was the debris made of??? ... It came from somewhere and I would want to know what it was and where it came from because there may be more..." No idea, but I think it is something that just fell into the open fittings while they were re-assembling the engine. Remember, the heads were off, so the return line was sitting there, disconnected. And, in the back of the engine bay with poor access, it would have been easy for stuff to just fall in there and be hard to spot when they dropped the heads back in. At least, that's my guess. FWIW, I don't think it came from the supply side and then traveled through the rail(s). -Sean http://OurOdyssey.BlogSpot.com | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 453 Registered: 11-2005 Posted From: 63.97.117.39 Rating: N/A |
Sean, There is a small Al cone shaped disc with a center hole that is made just for this purpose. I used them in my old airplane hydraulic fittings which were 1200psi plus, both in hydraulic components and the brake system. They are soft and comform to any malformed sealing surfaces. I have never used one as large as 1/2" but have no doubt they are available. I'd mail you a couple if I had that size but all I have is a few 1/4". Try an aircraft supply place or the local airport aircraft repair. I've never had one leak. Needless to say one does not want to tighten these too much. On second thought, these things could be sold in auto parts stores, especially ones with truck parts or maybe one of the bus places might have them since your lines are pretty large. (Message edited by gusc on August 17, 2007) (Message edited by gusc on August 17, 2007) | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 664 Registered: 1-2003 Posted From: 72.171.0.147 Rating: N/A |
Gus, Perfect -- just the solution I was looking for. I'll call a couple hose shops on Monday. I doubt aircraft repair would have them as big as #8 -- that's a hell of a hydraulic line. I would imagine found only on commercial jets in that size. I had occasion to talk to the mechanic at S&S who worked on our coach this afternoon (the reason for the call is a whole other story unto itself -- apparently, I've been leaking TranSynd at $40 a gallon across seven states), and he confirmed that he did not run the bucket test long enough for the Davco to drain, so there may well be air coming in upstream of it (or, as we've said, an upstream restriction). I want to fix this flare fitting issue first, and, if that doesn't solve it, I'll start looking for blockage at the tank. Right after I fix the tranny. -Sean http://OurOdyssey.BlogSpot.com | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 454 Registered: 11-2005 Posted From: 63.97.117.29 Rating: N/A |
Sean, !/2" flare is a common size on gravity flow light aircraft fuel systems, I had 1/2" on my '47 Stinson but the pressures were very low. My Navion had a pressure system so the lines were much smaller. So, it won't hurt to ask and again I recommend calling a NAPA store. Sure would make it easier, auto parts stores never cease to surprise me at their inventory or next day access. | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 665 Registered: 1-2003 Posted From: 72.171.0.147 Rating: N/A |
Gus, Are those AN or SAE? -Sean http://OurOdyssey.BlogSpot.com | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 455 Registered: 11-2005 Posted From: 63.97.117.39 Rating: N/A |
All the taper fittings I mentioned are AN but the soft Al cones will probably even make unlike tapers seal. It takes care tightening them, not too tight, and they probably can't be reused because Al work hardens so easily. Well, I have to retract that. These cones are so soft they must be pure Al so they probably don't work harden afer all. However, they are certainly inexpensive and work great, never had one leak. (Message edited by gusc on August 19, 2007) | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 488 Registered: 7-2006 Posted From: 66.217.105.33 Rating: N/A |
"As far as the Davco, yes, Chris has given me something to think about, but I have no evidence whatsoever that it is having or causing any problems. " Davcophaelia: [ N. dav-koe-fal-I-ah ] A fetish for ownership of Davco fuel filters. Symptoms: Individuals lust for the viewing of the fuel flow; the seemingly automatic filling and emptying of fuel from the filter, and engine problems associated with the failure of the filtering device. Cure: No known cure. </yanking_of_chain> |
