'86 F250 6.9 no fuel pressure at schraeder

[jaymack77]

Hey,

My truck (1986 F250 2wd 6.9 L diesel) has been driving fine lately, except for an almost unnoticeable surging as I am driving. It would feel a little extra gutless, and then like I am pushing down the accelerator. Didn't worry about it too much. This morning I went to start it, and when it fired, it ran for about 2 seconds, then coughed and stopped. After that, it would just turn over and over without firing. I tried to re-prime the system, but no diesel was coming out of the schraeder valve when I had my wife turn it over. The fuel filter was only half full when I removed it. I have been reading about these "lift pumps" and it looks like that is what gets the gas from the tanks to the injector pump. Is that right? Is there no standard fuel pump on these systems? Sounds like they are simple enough to replace. Does that sound like the problem? I am grateful for your time. Jeff McLean

[yotermanic]

As a rule of thumb, I always just went by whether there was fuel at the schrader valve or not. I think, but am not sure, that the pressure is like three pounds or something, the lift pump's main job is to get fuel to the injection pump. They're mechanically driven and mount on the front right of the engine. After replacing it be sure to prime that fuel filter and be ready to bleed air at the injectors if you have to. You do this by cracking the lines one by one and cranking until fuel spills out steady. Sometimes you get lucky and the truck'll start after cranking a while and not bleeding injectors. Some brave or stupid souls will use ether to get it to start initially and let the injectors self-bleed. While I will admit to doing this before, I will not reccomend it because I've seen diesels run away and it is not pretty. Anyhow, good luck with it and let us know how it turns out.

[ModMech]

Either the "lift pump" (which IS just a simple old-style gasoline fuel pump driven off the cam) is bad, or you have a leak in the fuel lines between the tank and the lift pump.

Remove the HOSE from the lift pump (lower rt front of the engine), and attach a vacuum gauge to it, crank the engine and it should pull a vacuum to over 20" in one or pumps (revolutions). If not, replace it.

If it DOES pull a vacuum in a revolution or two, then I would suspect that you have a leak in the fuel supply hose (dry rotted etc).

[jaymack77]

Gotter done- the lift pump cam had seperated. Easy fix and the truck also bled easily. Thanks for your info.

Jeff