Engine/Transmission (1994 - 1998) fuel pressure question

[JWalsh]

I have a mechanical fuel pressure gage with an isolator installed on my 1994, 4X4, 5 speed. Since installing it about 6 months ago the fuel pressure read constant between 19 psi and 25 psi depending on the engine RPM. Now for the past few days in the morning it is still constant but in the afternoon it oscillates so rapidly around the above pressures that the needle is a blur. It also seems to be getting worse. Does any one out there have any ideas? Any help is appreciated.

 

[illflem]

Two possibilities, both caused by warmer fuel

1) Are you using a needle valve or snubber? If not you should be even with an isolator. Pulsation without a damping device ahead of the isolator will weaken the isolator's diaphragm that beforehand was dampening the pulses. If you are using a needle valve it may need to be closed down more. More info here https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=70109



2) Your overflow valve spring is getting weak, warm fuel makes it worse. The pulsations you see are coming back from the injection pump.



I suspect #2 since your pressure was on the low side to begin with but if you don't have a dampening device install one, it will set you back all of $4.

 

[JWalsh]

Thanks for the suggestions. I installed a needle valve and snubber. That took care of the oscillations. At idle the fuel pressure was a steady 19. 5 psig and at 2000 RPM 25 psig. They were difficult to find. Got them from Grainger. Had to come up with name for my own company. I also got an overflow valve from Piers Diesel. That increased the pressures. at idle 25 psig and at 2000 RPM the gage is pegged at 30 psig. The new overflow valve internals are slightly different from the original. I was thinking the warmer temperatures had something to do with it. Again thanks