| Author |
Message |
Jack Conrad (Jackconrad)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 23, 2005 - 7:40 pm: | |
I installed an electric fuel pressure gauge in our MC-8. The gauge works only it reads backwards, At ilde it shows about 70 PSI and decreases to about 30 at higher RPM. I have a mechanical pressure gauge in the engine compartment that is reading correctly. I double checked the connection on the gauge. Sender lead is connected to S terminal, 12 volt switched power is connected to I terminal, and the case is connected to ground. The sending unit is installed in a tee fitting on the secondary fuel fliter discharge. The sender has 2 terminals Sender lead from gauge attaches to one terminal and the other goes to ground. I tried reversing these 2 leads with no change in gauge operation. Any suggestions? Thanks in advance, Jack |
Sammy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 23, 2005 - 9:14 pm: | |
Jack, did you use teflon tape on your tee fitting??Check continuity to ground from the sending unit to chassis ground.
Sammy |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 23, 2005 - 10:04 pm: | |
Sammy he indicated that he has an isolated ground sender...
Wait a minute... Do you have an electric fuel pump? If you're using a (mechanical pump) MUI type Diesel, the pressure SHOULD drop as the RPMs increase. This is because the fuel rail flow is being split between the injectors and the return line.
Which would mean:
Idle RPM - most of the fuel is bypassing the injectors and passes out the restrictive fitting on the return-side line, which means the pressure will directly relate to how much fuel the pump is squeezing in the fuel rail as opposed to how much can get out (high pressure).
Max RPM - about 2/3 of the fuel is exiting the fuel rail through the injectors, flow is increased by the RPMs but the pressure should drop because there is a higher exit volume in the fuel rail (lower pressure).
If you have a mechanical pump, it sounds like your pressure gauge is workin'.
Cheers!
Tim |
Sammy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 23, 2005 - 10:09 pm: | |
Thanks Tim, I misunderstood Jack's post.
Sammy |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 23, 2005 - 10:21 pm: | |
You did point out a good concern Sammy... there shouldn't be teflon on a fuel line (teflon breaks down in fuel), they are supposed to be taper fittings. One more detail to take care of (gauge difference): I presume the electric gauge is at the dash board.
Questions:
Are they (the gauges) the same at idle? Are they moving the same when you change the throttle position? Are they the same when you push the engine to the govenor?
These questions would need to be answered before a determination of (or whether you have) a problem.
Tim |
Jack Conrad (Jackconrad)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 8:20 am: | |
No teflon tape. My mechanical gauge, installed in the engine compartment and connected to the same tee fitting shows 30 PSI at idle and increases to about 65-70 when the engine (and pump) RPM increases to max governed RPM. I am going to call the gauge manufacturer tomorrow. It seems like the sending unit is sending the signal backwards (low ohms when it should be high ohms and visa-versa) Jack |
Jim Ashworth (Jimnh)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 8:55 am: | |
Jack- I think you have the answer. You might think about changing the location to between the primary and secondary filters. This way, if the primary gets plugged, the pressure will drop and if the secondary gets plugged, the pressure will rise. Just an easy way to know what's happening inside the filters. I think the idle pressure is a little low. My engine runs 60 psi at idle and 65 at full speed. If I let off the throttle at full speed, it goes to almost 70 since no fuel is being consumed.
Jim |
Tim Strommen (Tim_strommen)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 10:12 pm: | |
Yeah, you definately have a problem. Before calling the guys at the gauge place, take a resistence reading from the gauge at both RPMs (idle/max) and see if they are similar to standard readings (240W for 0psi, 30W for 150psi).
May be a quick thing to fix, or not...
Cheers!
Tim |
Chuck Newman (Chuck_newman)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 24, 2005 - 11:31 pm: | |
Tim and Sammy,
When I install a new fuel filter, and may add a tee in the future, what do you recommend for NPT sealant? I know not to put anything on flare fittings.
Thanks,
Chuck Newman
Oroville, CA |
Sammy
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 25, 2005 - 6:17 pm: | |
Chuck, I recommend a product called "Leak Lock".
It comes in a small plastic blue bottle with a brush, or a small squeeze type plastic blue tube.
It should be used sparingly.You can find it at your local plumbing supply house, or plumbing section of your favorite hardware store.
I've had excellent results with it.
Sammy |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 25, 2005 - 8:18 pm: | |
Any of the pipe thread sealants approved for natural gas piping should be OK. It has to be good for petroleum products and since gas lines use cathodic protection it must be conductive.
I have never used it for automotive fittings since I never had a problem with teflon tape on sensors. It is hard to believe that you could tighten up a tapered thread and not have any metal to metal contact. There are other reaons for not using teflon tape so start at the second thread and put on not more than two wraps. |