| Author | Message | ||
| Steve Krane (Steve_krane)
Registered Member Username: Steve_krane Post Number: 29 Registered: 1-2007 Posted From: 76.176.108.66 Rating: N/A |
Lost fuel pressure on CA 76. Bus ran for maybe a mile with the fuel pressure gauge reading near zero, enough time to get off the road. Bus was towed to Rush Truck in Escondido. I haven't kept much fuel in it over the past year (waiting for the next AZ run) and figured maybe condensation and bacterial growth plugged a filter or a line. The shop replaced the fuel filters which looked OK according to them. They claimed that the problem was a 12VDC battery disconnect and the fuel rail air actuator solenoid was dropping out. I pointed out that the engine start current goes through that switch so how could it provide too much resistance for a solenoid. Anyway, the bus was running and I was just going to take it home and fix it. After a mile, fuel pressure started to go low again. Same as before. The guy came out and primed it and we drove it to the Shell station and filled it up (it had about 40 gallons in it). It did make it back to the shop, barely. The way the mechanic was priming it looked pretty easy, not sure how good though. He would take the line off the fuel pump inlet and put a little positive air pressure on the tank, just enough to get the diesel to flow. After priming the fuel pressure is 10-20 at idle and 60 at revs. It goes down gradually and might pick up a little pressure sometimes but eventually settles at zippo. What do you think? Sucking air in the line from the tank? Tank pickup? Clogged line? What's the easiest way to tell? | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1095 Registered: 10-2003 Posted From: 71.58.48.228  Rating: N/A |
after idling for a while, shut off engine and remove primary fuel filter; is it clear full or partially full? If it is not full, you could have a n air leak in suction line or fitting between pump and tank, or tank pickup could be sucking some air. to check the line to tank, you could unhook it and run a line from the fuel filler opening to the inlet in the primary fuel filter and see if it runs ok. Just temp duct tape it to outside of coach, bleed out the air and take it for a spin. you should have a one way check valve in this line to keep fuel from running back to tank. You could first start with a 5 gallon can of fuel with a short hose in it hooked to the primary fuel filter inlet and run engine and see how the pressure does first before running the other line. Just some ideas for you. | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 428 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Steve, John has the answer! I had a badly corroded and leaking tank when I bought my bus, and I had to get it to a welding shop. The answer was a five gallon can in the front bay, with both the suction and return lines connected to it. Worked like a charm, and in your case, will narrow the problem down to manageable size. I don't buy the electrial theory either, but an easy solution is to take the shutdown cylinder off the engine. Needless to say, if this clears the problem, look for either a bad skinner valve, or a loose connection or ground. Regards, and please post back with what you find. George | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 639 Registered: 11-2005 Posted From: 208.54.200.37 Rating: N/A |
Having been through a leaking check valve problem I agree with the sucking air into the line from fuel tank to pump and the less than full filters theory. I don't think the shutdown cyl has anything to do with fuel pressure?? Also, the check valve at the primary fuel filter will only be a problem after the bus has been sitting for a while like overnight. It won't be a problem as long as the engine is running. If you have a fuel line leak and pressurize the fuel tank line with fuel you will have a diesel leak at that hole which sometimes makes it easier to find. I don't recommend air pressure into the tank because it is too easy to bulge or blow a hole in the tank. There could be a leak at the filter connections and bowl gaskets which will easily show up when pressurizing the fuel line at the tank. | ||
| Steve Krane (Steve_krane)
Registered Member Username: Steve_krane Post Number: 30 Registered: 1-2007 Posted From: 76.176.108.66 Rating: N/A |
Thanks for the tips. And the answer was... sucking air through a fitting at the check valve in the suction line. I suspect it may have been due in part to vibration from the power steering line which was not well isolated from the fuel line. The power steering pump cavitates and makes noise and vibration when first started on a cool morning. One thing leads to another. I should be checking for leaks, hose, tube, and wire isolation more better. | ||
| Bill Young (Billyoung4106)
Registered Member Username: Billyoung4106 Post Number: 1 Registered: 5-2008 Posted From: 68.209.175.133 Rating: N/A |
I have this same problem.Running out of fuel. Fuel filters will be low.Little fuel pressure so I changed the pump.The claw looked good. Bus runs off a can of fuel at the back but not on a longer line to the tank. So I checked pressure again and still barely move the needle on the gauge.Any ideas. Bill in NC, | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 436 Registered: 8-2006 Posted From: 76.91.197.153 Rating: N/A |
Bill, I feel strongly that your problem will be the same as Steve's, a suction leak somewhere between the pump and the tank. Start to find it by checking all of the fittings for tightness. Remember that a suction leak will pull air into the line, instead of fuel up from the tank, and won't leak any fuel out where you can see it, as in a leaky flex hose. The primary filter is also under suction, so check to see that the gasket is properly positioned, and the filter (or housing) is tight. Do you notice any difference in performance when the tank is low or full? I have seen a hole rusted in the side of a fuel pickup tube about halfway up, the engine ran fine with over a half tank, then starved for fuel when the level got below the hole. Drove a bunch of pipefitters crazy. If you don't find loose fittings, and have a check valve at the tank, disconnect the line at the filter inlet, and connect a fitting so you can apply some low pressure air, then get out the soapy water sprayer, and squirt! If no check valve, disconnect the line at the tank, and make a plug with a flare fitting and a cap. Post back and tell us where you found it please. George | ||
| Bill Young (Billyoung4106)
Registered Member Username: Billyoung4106 Post Number: 2 Registered: 5-2008 Posted From: 68.209.175.133 Rating: N/A |
There are check valves at the back before the filters in the input and return line. I replaced both. The input first ,then the return althrough I didn't think the return would cause the problem.The only axcess to the tank insides is through the fuel input.The pickup seems to be welded in. So I pulled the tank out a foot after getting most of the fuel out, and felt of the pickup tube. nothing.. I blew in it with my finger over the bottom and didn;t detect a leak that way but not a very effective way to find a leak there but I knew no other way to try.I did run it one time off fuel at the back of the bus and then tried running a line to the tank thinking I was close then but it wouldn't pull fuel that far so thats when I put the gauge back in the sec filter and got no pressure still. I need to step back from it a day and try something again.It is really starting to get me... | ||
| Bill Young (Billyoung4106)
Registered Member Username: Billyoung4106 Post Number: 3 Registered: 5-2008 Posted From: 68.209.175.133  Rating: N/A |
Well I worked on my bus today.It runs on a line from just beyond the check valve to the tank and has good fuel pressure.Tomorrow I'll get some soap water mixed up and start spraying. If it's not right around the check valve and short line there it's going to be hard to find with all the lines running in the troff togather with all other hard lines. It might be better to cut that one lose and run a whole new line to the tank. Well I'll let you know what I find . Thanks for all the input | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 658 Registered: 11-2005 Posted From: 208.54.200.129 Rating: N/A |
Bill, I'm not clear on the location of the check valve you mention. I assume it is the one on the supply line into the primary filter like a 4104. If so, hook a generic electic auto fuel pump into the tank outlet then to the fuel line. In other words disconnect the tank outlet connection and insert the pump between the tank and supply line. Run the pump to see if fuel leaks anywhere along the supply line up to the pump. This pressurizes fuel into the complete fuel suction system and fuel will leak from any point which could suck in air under normal operation. This checks out the complete fuel suction system in one operation. If no leaks show and the pressure is still low you probably have a hole in the fuel pickup inside the tank. To check out the tank pickup system use a small container of diesel and run a hose from the container to the pump. If there is proper pressure and the engine runs ok you know the problem is in the tank. This is also a good way to recharge the fuel line when the injectors lose their prime. | ||
| David Evans (Dmd)
Registered Member Username: Dmd Post Number: 238 Registered: 10-2004 Posted From: 96.232.83.216  Rating: N/A |
Bill, you should be able to remove the p/u tube. Our Gm has a screen on the bottom of it and it gunked up once with sludge and caused a gradual loss of power. Good luck | ||
| Bill Young (Billyoung4106)
Registered Member Username: Billyoung4106 Post Number: 4 Registered: 5-2008 Posted From: 68.209.175.133 Rating: N/A |
Thanks for all the help ..The problem was in the input line.It still has the hard line running down the incloser in the middle with all the other lines. Rather than trying to go through all that I opted for the easy way and run a rubber fuel line to fix it. I have found from talking to other owners that these either came out with different style pick ups and check valves and other things or have been modified a lot over the years by different people. I suspect the lader. Thanks Bill | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1139 Registered: 10-2003 Posted From: 71.58.48.228 Rating: N/A |
I hope that is a good rubber line and not automotive fuel line. Most of that stuff is not rated for suction use. Will work for a while though. That main line should originally be heavy copper or steel. The problem is, most likely at either end unless someones messed with it over the years and it is rubbed through; highly unlikely. | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 665 Registered: 11-2005 Posted From: 208.54.200.27 Rating: N/A |
Bill, If you mean you now have a rubber pick up line into the tank it may curl after a while and not suck fuel near the tank bottom. If that is what you mean you should use some type of hard line to keep the bottom of the pickup at the same level. | ||
| Bill Young (Billyoung4106)
Registered Member Username: Billyoung4106 Post Number: 5 Registered: 5-2008 Posted From: 68.209.175.133 Rating: N/A |
It's not the pickup. I connected to the top of the tank and run 25 foot to the back at the check valve one line short of the H block and the primary filter. One personed e mailed me and told me his coach has had rubber line on it since he brought it serveral years ago. If you-all think it will not hold up I will make one up of Hydrylic line. That should hold up. Bill | ||
| Stephen Fessenden (Sffess)
Registered Member Username: Sffess Post Number: 730 Registered: 1-2002 Posted From: 66.38.120.219 Rating: N/A |
I have seen a small diameter pex tubing advertised as a fuel return line. If it can handle all the varied components of diesel, it might make a good pickup. I have had fuel hose that was supposed to work with diesel eaten up in 3 years. I have seen plastics in good shape after 8 years. |