• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Help. I’m reaching my limits.

Yup, loosen the cap is next.

Any bubbles in the clear ip return line? That can be air intrusion or if tank /cap isn’t venting the fuel under vacuum will self aerate (boil while still cold) which is amazingly hard on the ip, and can ruin a brand new ip in a week if bad enough. This will show up as no pressure if the gauge is tapped at the ip inlet. If pressure is present and bubbles then it is simple air intrusion.
 
Will L. said:
Yup, loosen the cap is next.

Any bubbles in the clear ip return line? That can be air intrusion or if tank /cap isn’t venting the fuel under vacuum will self aerate (boil while still cold) which is amazingly hard on the ip, and can ruin a brand new ip in a week if bad enough. This will show up as no pressure if the gauge is tapped at the ip inlet. If pressure is present and bubbles then it is simple air intrusion.
Click to expand...
I’ll check the cap. Wasn’t aware the pump return is clear, will check that too. Thanks.
 
No, you need to put clear line on it. Thats what I was saying back in post #9.
Go to any hardware store. Buy 6” of clear 1/4” tubing and two hose clamps. Should be under $5 together and takes a couple minutes to swap out. You will have to replace it every 5 years or so depending on your weather, but it is always a simple pop the hood and look diagnostics forever after that.
Bubbles= bad.

I also mentioned trying a spare pmd. If you dint have one yet, you need one. It is like a spare tire. You may get lucky and never need it- but right now you need it for diagnostics. There is no electronic tests- only replace with known good to see if the one you have id failing.

but try undoing the fuel cap first since free and easy.
 
Did you ever buy an ACDelco OPS? and replace it.

It is a 94, if you see air in the system means LP is not working.
LP not working can be caused by bad OPS or non ACDelco OPS.
 
Which is why you should, no, must use the OPS fuel pump relay with a manual override switch so that the fuel pump is not drawing its amperage through the OPS when the oil pressure comes up (engine running) and the contacts close, but instead the OPS now energizes a relay and the contacts of the relay takes the fuel pump's amperage load. The manual switch energizes the relay, so that you can 'prime' the IP before starting or manually run fuel so you can refill the FFM after changing your filter.
 
Just in case anyone is curious, I blew the line from fuel pump back into tank, and problem has not reappeared in a couple weeks now. As luck would have it though last night the trans started to feel like it was slipping in all gears. Rpms would rise and speedo was bouncing around as well. Wondering if speed sensor could be bad and causing trans control to affect torque converter?
 
Dang.
On the last problem of fuel, if something got through there and was plugged, it can happen again. When there is a restriction of lift pump is bad, the ip will try sucking the fuel through it and it wears out the ip really fast. Lesson has been learned that putting a T just before the ip for a fuel pressure gauge that lives on the dash so you can see it just like oil pressure. When pressure falls you know something is going on before breaking down. You didn’t really remove the issue, just pushed it out of the way for the moment- expect the returning problem.

Also the clear return line that was mentioned is a good idea all the time so when something goofs in the future, and eventually something will, you can just pop the hood and look.

When we were suspecting a possible pmd starving the fuel, something we didn’t mention is bad grounds can mess with pmd and ecm. Remove and clean the grounds especially the one by the trans dipstick, and battery cable Ground. I would also do the ecm ground wire. Ecm include transmission control as part of it’s function, and usually cleaning that ground is a once every 30 year. Doing those grounds is free and only takes 1/2 hour and is best to eliminate before chasing other things.

I wonder if the fuel starvation effected tc locking in and out beating up on it.

The speed sensors that are on driver’s outside of transmission and transfer case if applicable (please fill out your signature with truck details and modifications- it really helps us think through issues) are easy to take out, clean off and see if any debris is picked up. Honestly doing it rarely solves anything (only seen it 3 times out of 15 or so) but is easy and free. If debris is there it’s ahuge warning that trans is about to be redone.
Really the next step then is scanner/ computer on it to see what’s happening and a pressure gauge following GM’s trouble shooting list.

I stumble my way through trans. One of the real transmission folks probably has better
 
So it turns out the speed sensor harness wasn’t fully seated and was thoroughly coated in sludge. Got it sorted out and so far so good. Fingers crossed. I don’t know but I’m guessing the loss of signal and resulting delta between input and output was causing the slipping feeling as it hunted for appropriate gear.
The fuel delivery problem has not resumed either. I know I didn’t really “fix” anything but I’m still counting it as a win😁
Thanks for all the helpful replies. I put a quick rundown in my sig but not sure if others see it. Be safe everyone.
 
Your signature shows up just fine, @Matthew Thieme . Amazing what clean, fully seated electrical connectors can do for clearing up gremlins in the system. You'll probably see it over and over again on here, but can not iterate enough the importance of good, clean grounds (especially the two on the passenger side intake manifold) to help these run right. Being a '94, you should very seriously consider the OPS/lift pump relay harness modification that @LeroyDiesel (also a vendor) sells on here, so that the LP doesn't pull its full current through the OPS to run.
 
You must log in or register to reply here.
Back
Top