erratic rail pressure

[BMeier]

I am currently having a problem with my rail pressure jumping around. When I start my truck it will be at 5500 psi and work fine after a few miles when I pull up to a stop light the pressure will drop to 2000 psi and come back up sometimes die. Going down interstate the rail pressure will be at 12,000 and drop to 8000 psi briefly. I have a low pressure light with a CAT fuel filter after the factory filter. The light never came on, I checked lift pump pressure and it was at 8 psi. I then tried a new FCA and the problem continued. While troubleshooting all of a sudden my light would flicker. I replaced filters and it still flickered. I hooked up a mechanical pressure gauge and the lift pump would drop from 8 psi to 0 psi and everywhere in between. Then it finally stopped all together, I have a new lift pump ordered, if the pump is failing but the pressure is good at the time of the rail pres drop could this cause my erratic rail pressure? Once the pump stopped all together and the CP3 starting pulling fuel in, the rail pressure smoothened out, it doesnt really make sense.

 

[LakeLife79]

If your lift pump is acting up it will definetly effect your rail pressure. What kind of lift pump, stock or aftermarket?

 

[BMeier]

Its the original lift pump, I ordered the replacment from Genos. I wanted to go with an aftermarket pump, but money is tight with the holidays here.

 

[Bob4x4]

You can totally bypass the stock pump,it will run just fine to test

 

[BMeier]

how do I bypass it?

 

[Bob4x4]

Run a hose with an inline filter from the fuel line before the pump all the way up front to the CP3. It will start and run with out a lift pump.



Bob

 

[Joseph Donnelly]

Is it really the rail pressure, or the gauge. in my experience, the TST gauge is very reliable, but the diPricol is very touchy. If the wires going to the gauge are near other stuff, and sometimes if it seems they aren't, the gauge is erratic. Definitely don't route the wires through the "big grommet" in the firewall. It also needs "clean power" meaning you can't just use a Scotchlok on any hot wire to power it.

 

[BMeier]

Yeah, it is the rail pressure acting up, the engine sputters when the pressure drops. I took it in and the dealer installed the new in tank lift pump under warranty today. My motor runs like a clock now. I have heard about the touchyness of the dipricol gauge so I made sure I wired it cleanly. I have had really good luck with the gauges so far, I have 70,000 miles on the motor with the pricol gauges and no gliches. Any way the new lift pump fixed my problems, the engine runs great again.



Thanks for all the ideas.