01 with fuel problems

[Elliottequip]

truck has 2 year old faas pump. On a relay because the ecm is not sending power to the pump. Just replaced the injection pump. Only getting 5-10psi. Has wiring the lift pump to a relay killed it.

 

[BarryG]

While the ecm powers the lift pump it should not care where the power is coming from. I seem to recall that at "key on" the ecm runs the pump for 5 seconds, if you bump the starter it runs for 30 seconds. During the normal start up sequence it runs for 5 seconds then when you move the key to start it has full power. The lift pump does not care where it gets power and as long as it is wired correctly should not pose an issue to the pump.

Don't know where your pressure gauge is plumbed but if it is post filter could be a dirty fuel filter, could be a faulty gauge, the fass is getting weak for whatever reason, could be the pump return pressure mechanism (spring I think) is going south as well or junk in the pump not letting the bypass operate correctly. Could be air getting into the system. Could be a bad overflow valve on the VP though that is fairly rare that they really go bad (iirc a new pump does not include a new overflow valve).

Not in any specific order I would break out the multimeter and verify that the pump is getting 12 volts, check the fuel filter, verify the fuel pressure with another gauge, look for fuel line/connection air leaks. A variety of other things could be an issue such as delaminated fuel line pretty unlikely but has happened, junk in the tank clogging the pickup screen.

 

[ed9824v]

I have told the ecm serves another purpose, and that is to pulse modulate the 12 volts to prevent too high of a pressure at start.

 

[BarryG]

That I believe is correct and forgot about it when writing previous post. Though it is funny as the oem pump cant put out enough pressure to make it an issue and the aftermarket pumps, at least the ones that can provide enough pressure to cause an issue all have return bypasses in them so again not really an issue especially since the oem could care less about aftermarket pumps. I know on my 01 it had no problem running 18-20 psi at startup most of the time or even higher at times though they were short. The modulation I think is more for the vp44's protection than the lift pump.

I never used a fass when I had my 01 so am not real familiar with them but I do know that there were threads about them with pressure issues over the years. Not saying they were bad pumps at all, many many happy people using them I just chose a different pump route. Might be worth a search on here to see if any of them have tips/tricks/advice on how they solved their problems.