Sounds like 2 possible problems,a bad oil pressure switch and sucking air somewhere in the fuel supply side.

The oil pressure switch supplies power to the lift pump whe the engine is running and even though the gauge woks can still be bad.

Replace with AC Delco ONLY,and google OPS relay mod.

 

i checked every single wire on and below the motor and found nothing. everything looked to be in good shape. i put a new fuel filter on it. on the bottom of the fuel filter like the housing of it, there's like a plastic screw on lid. just above the 3 fuel lines that hooks in it, it seems to be leaking right there and was wondering if there's suppose to be a oring there. i think it must be a wire or something cause on the way home tonight it was jerking and what not like it always does, and the voltage drops quite a bit when it does it. like it'll be on say 14, and when the check engine light come's on and it starts jerking back and forth the voltage drops to like 12 or so. i'm really at a lost on this truck. it's driving me nuts!

 

The bottom of the filter housing holds the fuel heater,and yes it is a common leak place-new O-ring required.
While you have it out change the water in fuel sensor O-ring too and do not try and re-use the new fuel filter-they are not intended tio be taken on/off repeatedly and the O-ring tends to stretch and no longer seal.
'
Dropping voltage is an odd occurrence.

 

okay, i checked the ecm behind the glovebox and all the wires look good except the black ground wire that hooks to the ecm plugins the ground wire goes down and bolts into the side of the glovebox it looks like the previous owner messed with it and there's no butt connectors on it it's just twisted together. everytime i reset and check the check engine light codes their always different. could this ground problem cause all the trouble i'm having?

 

If its not a very good connection, then yes. I think the voltage drop may be part of this problem. Does this problem happen when you hit a bump?

BTW, Very good investigation work. Sounds like youre on the track to fixing it.

 

The voltage drop happens at random, its kind of weird. Because I shook all ECM wires and ground wires to the ECM while it was running and it seem to have no effect so I'm still not totally sure that is the problem. It's driving me crazy I've been searching and checking out every single wire. The break light wires seem to have a short cause they don't work but if you hit a bump they come on. Could it be possible that the short in the break lights that it could draw enough juice to where the lift pump or injection pump won't work correctly?

 

Grounds are the single biggest item to have clean and secure on these trucks,refer back to post #2 of this thread.
An bad ECM ground will sure cause your code troubles.

The brake lights should blow a fuse if there is a dead short.

 

no it doesn't do it when i hit a bump, it's just random like i could be cruising at 60 on a smooth road and it'll randomly drop. the break lights come on and off when you hit a bump also. i don't know if maybe it's drawing enough juice to where the lift pump or injection pump won't work right. i'm considering all possible ways .

 

Brake lights coming on after a bump likely means the brake switch needs to be adjusted.

 

injection pump $1800 happened to me