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Crazy Fuel Pressure?? 30+ at IDLE


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I have a FASS 95 with 3/8" (I believe) fuel lines.Fuel filters (inline and main filter) replaced about 5k ago.Last week, my fuel pressure started reading 30+. My gauge only reads to 30. As long as I'm pressing the gas, I get a normal reading (15-18, ~14 WOT). When I start the truck, the pressure has always spiked to 30+ for a second, then came right back to 18. It's just now STAYING at 30+..Called FASS and got instructions on how to take the pump apart and check the ball and spring. I'm in the process of finding a mechanic or someone to help me because I'm not sure I can handle it by myself. I also need to check that my gauge is working (It is a GlowShift...) but I can't check that untill Monday...Any ideas?PS: About 3 months ago, it would randomly spike to like 25, then come back to down to 18 PSI. It did that pretty often for a week, then quit...This fuel pressure thing is driving me crazy.:banghead:

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It sounds like your sender had probably been hammered to death by the pulses the VP creates while pumping, here is a good explanation. http://articles.mopar1973man.com/general-cummins/36-fuel-system/34-fuel-pressure-gauge-and-water-hammer-effects. I had a glowshift for my first gauge and it did pretty much the same thing. Its not so much the gauge or sender fault, there just needs to be some thing there to isolate both from the pulses.

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  • 3 weeks later...

This is why its a good idea to plumb in a test port when setting up a fuel pressure gauge. I didn't bother to do that the first time I set up my electronic fuel pressure gauge so when my sender failed I had to guess whether or not the problem was the sender, gauge, or pump. Turned out it was the sender but when I changed over to a mechanical setup I plumbed a "T" fitting in just before the isolator and added an OEM schrader valve to the third port so that if I ever have a reason to question my fuel pressure I can simply hook up a tester to that schrader valve.

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