thumper549

OK. Thought I had this solved...Not
Lift pump will die when Eng is about 1/2 warmed up. Sometimes I hear the Eng stumble and see the pressure drop to 0, Other times Eng. will just quit.
Ether way I restart / or shut truck off and restart and all is normal for a few and repeats the whole program.
This might go on for 10 minutes or less.
The rest of the day all will be fine
Too weird
If plug the truck in for 2 to 3 hours B4 use this seems to eliminate the problem.
Any guesses ?
It has to be a GO open some where...but the instant restart / fix is confusing me

Russ Roth

Mine did something similar when my LP was dying.

John Faughn

0 fuel is not good , not sure but I think the min. pressure is about 5-7lbs & up to around 12-15lbs .
What is the idle ?
That's also common to your description .

Hillcountry

Is it possible your fuel is gelling and causing issues/plugging the pump or fuel filter? I see from your sig, that it is probably pretty cold. Perhaps the plugging in keeps this from happening because it is keep[ing things warm. I only think this because you say when the truck is plugged in it does not happen...that suggests a temperature issue. Just a thought...it could also be the LP or the connection to it.

thumper549

The pressure will drop to 0. Upon instant restart goes right back to 10 lbs....there would be no time to warm fuel from a a gel state .(warm the paraffin)..I am darn sure it is electrical...( well pretty sure )

Hillcountry

Yeah..that makes sense...perhaps there is "gunk" in the plug which connects to the LP? Road salt etc...have you tried cleaning it? My only other thought would be to try hooking a volt meter to the pump itself to see if when the pressure goes to 0 the pump is indeed off. Otherwise it could be the pump. I would test at the pump and work backwards from there if it is electrical.

Busboy

Like hillcountry says check for power at the pump, volt meter or test light inside the cab would work. One other thought is your FP gauge mechanical or electric? If elect could be losing a ground?

dozer12216

At the two wire plug to LP. Hook a voltmeter to the white wire and ground. With engine running should be greater than zero. My memory is trying to tell me the pump is duty cycled after startup and you will not see full battery voltage all the time. If you see voltage and don't feel pump running, you have a pump problem. It sounds like issue will show up at idle, so should not be hard to figure what's happening.

thumper549

I think I need a schematic as to how the circuit works...
It starts and runs off the ign switch then transfers to the ECM ?
It always will start back up..so I think the problem is in the "run" circuit and some how goes to "open" during warm up
I could hook all sorts of volt meters to it, but that will not fix the intermittent open as they are in 1 of two diff places ?
Or I could Jerry rig a hot wire to it via a in dash switch.......but too hooky

Hillcountry

The pump is always being controlled by the ECM. When you are cranking it sends a lower signal to the LP so there isn't too much pressure at the VP44 when cranking. Once the engine fires, the pump should be getting full voltage. You only need to test at the pump itself. One voltmeter should be fine.

I also wonder if it is gauge issue? Is it an electrical gauge or mechanical?

thumper549

Then I have to assume for now that the ignition switch or the ecm is at fault ?
The restart is perplexing me

John Faughn

Never assume anything , testing can tell you what is working or not , while waiting for it to fail [ intermittent ] , check all the grounds , you will need that wiring diagram to find them all , especially the computer grounds .

Busboy

After rethinking your problem, I've decided there are ONLY two kinds of LP pumps. (1) Those that have failed. (2) Those that are going to fail. With that in mind buy a replacement pump and if it fixes it, it's fixed. If it doesn't fix it then you have a spare for when it does eventually fail. Some times you just have to "shot gun" stuff.

thumper549

.....Yea I guess so...just for drill and fun and to spend more $$$ on this pice of crap

thumper549

OK to narrow this dwn a bit more.
Out plowing last night and it set up a definite pattern
If the chassis is being twisted a little -front up or rear up and one end or the other has a twist to it the Eng shuts dwn.
It all happens fast .Sometimes I feel the miss , the pump stops (Eng keeps running ) other times it kills the Eng like the ignition switch is turned off for a instant.
I know for sure it is a open either to ECM or a loose GRD as I don't think the Eng will shut dwn if I loose just the lift pump.
What you think ?