Can not get 4 PSI on Lift Pump.

[bdv]

Have been having recurring Service Engine Soon Light with 17, 18, and 35 codes stored. Have also been having stalls and hesitation. I have been going through the checklist in the “Turbo Tips” article from the members’ section. Have installed new batteries to bring voltage backup as well as a new alternator and belt. Have installed a clear hose on the front of the injection pump to check for bubbles. Then I measured the fuel pressure at the fuel filter drain line with the fuel filter drain value open. Both cranking and engine running I had NO pressure. I put a new lift pump in and wired up a bypass switch (per article in TDP) also put in a new fuel filter. Ran pump and opened value on top of filter to bleed air. Unfortunately had not tightened filter enough and leaked diesel so tighten down enough no leaks. Was not able to get fuel to go through hose on top of filter to bleed into a container as I have done in the past. The funny thing is when I use the bypass switch I get a reading around 3 p.s.i. with the engine off (I can now clearly hear the pump running) , if I bump, switch pump on and off I can get the readings up to 5 p.s.i. with the engine off. If I start the engine I get the Service Engine Soon Light on 17, 18, and 35 codes stored and a NO pressure reading again. I have tested the voltage going to the pump with the engine on and am reading 14.0 volts. Have read in articles that system may be “Air Locked” but I don’t see any bubbles in clear hose on the front of the injection pump. Articles talk about cracking #1 injector. I have looked on drivers side very front, can see line from injection pump running to cylinder with compression nut on line (similar to fuel line at lift pump) is this the nut I would loose to bleed air out? Is the system air locked or is it something else?

Thanks for the Help. Brent

[TJ Moose]

I'm wondering - if you have pressure and pump operation with switch on/engine off, but no pressure and codes with engine running - that sounds kinda like the lift pump power that is controlled through oil pressure sender is crapped out. Either sender isn't driving, or something with that loop is out of sorts. If I'm reading past posts correctly, this is a different power source to the LP than when in key on/start mode. I'd say search posts for discussion of the power to the LP through the OPS.

[bdv]

Brent here, have taken voltage reading with the engine running and am getting 14.0 volts. So I take it the pump is getting enough juice. There is something reducing the psi. Thnaks Brent

[DmaxMaverick]

Try checking your lift pump pressure with the injector pump return line blocked, or the fuel line blocked before the I/P (ignition off, then on). If your pressure goes up, or fluctuates, the I/P is your internal leak, bypassing the fuel. This could also cause the pump to fail to develop consistent pressure (not enough to keep the injectors popping regularly, causing the miss/stall).

[rameye]

If you put your hand on the lift pump (while shes running) can you feel it pumping?

If you open up the air bleed on top of the filter (again while running) does diesel pour all over the place?

14 volts is nice, however you cant assume the pump is running because it has voltage. A bad ground or high resistance feed will give you great voltage but thats all. Wire the pump direct from the battery with an in line fuse and then check your pressures.

Also if your fuel line is blocked it will show decent pressure but you'll get a big zero for flow pressure. Maybe your old pump threw some crap in the line. Back flush the line.

Keep at it...

ram

[moondoggie]

Good Day!

What are the odds of a restriction between the tank & LP? This would allow pressure to build with close to no flow (bypass switch on, engine not running), & the pressure would disappear with the engine running.

I think there's some sort of filter on the fuel pickup in the tank; I have NO IDEA if they ever plug up.

When I ask what are the odds, I mean it: I have NO IDEA if this can happen or not, but it would certainly cause the flow/pressure symptoms you're describing.

Blessings!

[DmaxMaverick]

There is a "sock" on the fuel pick-up in the tank. They do get fouled.

Static pressure should still build if you are getting any flow at all. With a new lift pump, static pressure (and idle pressure) should be around 7 PSI, and should not drop below 4 PSI running. If you can't get that with good voltage, fuel is leaking somewhere, internal or external. With a worn out I/P, fuel can "return" at a much higher rate, and prevent building pressure. If there is no air present in the stream, the leak has to be after the lift pump. A failure to build pressure indicates a "bypass" condition.

Although rare, fuel can leak into the crankcase through the I/P. Keep a close watch on the oil level and condition.

[taznj63]

When you checked the 14 volts at the lift pump did you disconnect the connector from the pump and check for voltage?
You should check the voltageat the connector connected to the pump to get proper reading. On my truck I had great voltage at connector at the pump when disconnected but when I connected it to the pump the voltage was less than 1 volt.
My problem was a bad OPS...

Just for thoughts...