Hi,

so I had a problem with my lift pump not working, tested the pump with 12v to the connectors and it would do nothing, got a newish pump out of my parts truck and it ran for about a couple days, could turn the ignition on and it would start pumping. Then after those 2 days it just stopped. I checked all the wires and checked the pumps operation through 12v and it would run, so I figured my OPS was bad, again I got the one out of the parts truck but it didn't work. Then on my way to pick a new OPS up in the morning, the lift pump would work for a bit, but then turned off again!!

I went to NAPA to get a new OPS, put it in and tadaaa... the lift pump wouldn't work either. I noticed when I tried to tighten the OPS that the whole bracked where it is mounted, turned a bit towards me.
By then I was a bit pissed so I drove home and now the freaking truck won't shut off with the key, I had to stall it:eek: ????

I have a remote mounted PMD to the bumper and really no stalling issues anymore, just wanted to get my lift pump to work properly:( and now that!?

hope you guys can help me, thanks.

THe problem with your lift pump may be a grounding issue with the bracket. ALso if you need to shut the truck down, just unplug the fuel solonoid on top on the pump, it looks like a roll of quarters. Fix the bracket and see what happens and see that is has proper ground. These trucks are particular with the grounds.

Could be ign switch faulty

So I put my old OPS from the parts truck in again and now the truck shuts off again with the key!? I checked the lift pump again with 12v and it still works. The mounting bracket from the pump is made out of plastic so grounding there is not an option. I found that video of how to force the pump to run with those grounds and the fuse on the left side but nothing happened there???

Why are those grounds (if they actually are grounds?) from the Plus + circuit and not negative??? I checked all of them and found nothing wrong with it.

I'm about ready to throw the truck out of the window lol:confused: and why would the truck not shut off with a brand new OPS... for some reason there is not enough voltage at the lift pump to make it run:(

thanks again in advance, Bjoern

So I put my old OPS from the parts truck in
thanks again in advance, Bjoern
Your old OPS maybe bad already

That might be, but it didn't work with the new one either and the truck wouldn't turn off with the new one!

...after reading some more I will look for all the hidden ground wires and give them a good cleaning :)

That might be, but it didn't work with the new one either and the truck wouldn't turn off with the new one!

You mean the engine wouldn't physically shutdown?

I'm with whomever it was that suggested the ignition switch is bad. This isn't unheard of of these trucks.

If it wont shut down,that means to me the power to the PMD/ESO is not cut off.wich can IMO only be that the ign switch is fried

thanks, so does that mean with my new OPS I suddenly get the symptom of a bad ignition switch?? And yes I couldn't turn the truck off with the key and the new OPS. With my 2 other old ones it still works perfectly.

Let's say the ignition switch is bad, can I use the one out of my parts truck which is a 95 and already has the new style key/ interiour?

And has the ignition switch anything to do with my lift pump not working, which was my only problem in the beginning?

uh and is this the ignition switch or am I totally mistaken?

http://contentinfo.autozone.com/znetcs/product-info/en/US/wl2/LS309/image/2/

I guess the one from the 95 doesn't work cause it looks totally different and more expensive...

You could've had 2 problems
1 current,OPS and/or LP relay.You could've bought a new dud OPS

1 pending, intermittend ign switch, most times it works,some times it dont.

I think the 95 ign will fit a 94.

I'm confused about your statement regarding a "bracked" where your OPS is mounted. A stock OPS screws into the block below and slightly behind the Fuel Filter and has NO bracket. If it has been modified with some form of extension to make it more accessable, that might be your problem if it is loose, not allowing the applied oil pressure to activate the LP circuit within the OPS.

I think he meant the brass elbow fitting the OPS screws in.

Yes it is that brass elbow fitting. I checked my grounds today and they were fine, put the new NAPA OPS in there again and tightened that elbow fitting. Still the truck won't turn off with the key, although it always did with the old OPS.

Where is that lift pump relay located? That would be the only thing I haven't checked yet.

What is a "dud" OPS? Oil pressure is fine, right in the middle of the gauge usually...
So I guess I'll get an ignition switch and see what happens:confused:

won't shut off because you have hot wired it.

that could be too,cant see from here what he did.

A dud OPS is one that has a problem from the get go,oil press could read fine(dif circuit) and LP switch (second circuit)could be non operating( missing or misaligned contact)or something.

if it cranks ignition switch is good. If it won't shut-off he has bypassed the fuel supply pump relay and it's getting 12v feedback to the pmd.

Well all I did is switching the OPS, so that new one might be bad from the beginning, although I could turn it off like 2 times right after I installed it.

It was the cheaper one of the two they had available, hope I can return it. Good thing to know that my ignition switch is good when it still cranks :)

dont count on it,power to the pmd and ESO comes from the ign switch.

...since the switch for the 94 isn't too expensive I'll try that route as well... after that I'll just have to risk my injection pump.

...since the switch for the 94 isn't too expensive I'll try that route as well... after that I'll just have to risk my injection pump.The IP has notting to do with the probem.Its like blaming the lightbulb for not shutting of when you flip the switch

no I meant when I can't get my lift pump to work the IP will have to do all the work and I risk it that way!

I just looked around again and found a cable tapped into one port (the furthest to the right) of my lift pump relay, followed it and it went into the cab under the instrument panel and was hooked to a "blu" port. So I pulled it out, started the truck and it shut off with the key! So someone before actally hot wired my truck:rolleyes: for some reason and maybe the new OPS interfered with it.

The last thing to check now is that lift pump relay, I'll get it from my parts truck. Should that lift pump relay make any "clicking" noises or anything indicating its working condition?

Thanks

I just looked around again and found a cable tapped into one port (the furthest to the right) of my lift pump relay, followed it and it went into the cab under the instrument panel and was hooked to a "blu" port. So I pulled it out, started the truck and it shut off with the key! So someone before actally hot wired my truck:rolleyes: for some reason and maybe the new OPS interfered with it.

The last thing to check now is that lift pump relay, I'll get it from my parts truck. Should that lift pump relay make any "clicking" noises or anything indicating its working condition?

ThanksSneaky little gremlin eh. Now that makes sense,it fed back trough the new OPS and kept the PMD energized.

the relay is prob good if the engine starts ok,it works only in start mode to power the LP before the OPS takes over.

oh ok, so all I got to do now is find out why the lift pump is only getting about 8 volts. I'll switch the relay anyways just to make sure. It feels like I'm getting closer and closer to get the LP running :)

clean grounds,pass side rear off head grounds LP

oh ok, so all I got to do now is find out why the lift pump is only getting about 8 volts. I'll switch the relay anyways just to make sure. It feels like I'm getting closer and closer to get the LP running :)

I'm with Bison, clean those grounds...but if you can't trace back your low voltage issue you could always run new wiring - it's possible you have corrosion somewhere that is causing high resistance on the + side.

I had a few underhood wires on my truck in this situation and did a lot of rewiring a few months back when I replaced the PMD. Some wires I just pulled and physically replaced, and others I just made new feeds for, switched accordingly of course.

Thanks, I already found some of my grounds and the one on the passenger side frame was just hanging down unattached. There was another screw with grounds on the cylinder head passenger side and as I removed it coolant came out, ooops :)
All those + wires next to the lift pump relay look like they could use a good cleaning, too cause that forced LP run test didn't work for me where you tap into that one 20 circuit breaker.

so here is an update:

I went and bought a ACDelco OPS since that is the one everybody recommends, put it in and started it up and my lift pump was running, fuel came out of the fuel filter vent. So all was fine, shut it off and it would run for a bit longer.

Then I drove for a bit and decided to check it again and now it stopped working again!???? Before I put the new ACDelco OPS in I did those force LP tests where you bridge the orange and gray wire from the LP relay and it ran, now it won't even do that!? Also the bridge from the orange and gray wires from the OPS worked before and now, not! I tried 12v directly to the LP and it works there!:confused:

All my fuses and grounds are in working order, at least the ones I could find, hopefully there aren't any more. I got a 12v relay to do the mod in the next days.

I'm about ready to just drive it like that and stop careing about that stupid LP:mad:

LOL that stupid LP is what keeps the IP from working overtime and saves the IP from having to suck fuel allllllllllllll the way from the tank, and at less than a tenth the cost of an IP, it would be advisable to get that LP in working order!

so here is an update:

I went and bought a ACDelco OPS since that is the one everybody recommends, put it in and started it up and my lift pump was running, fuel came out of the fuel filter vent. So all was fine, shut it off and it would run for a bit longer.

Then I drove for a bit and decided to check it again and now it stopped working again!???? Before I put the new ACDelco OPS in I did those force LP tests where you bridge the orange and gray wire from the LP relay and it ran, now it won't even do that!? Also the bridge from the orange and gray wires from the OPS worked before and now, not! I tried 12v directly to the LP and it works there!:confused:

All my fuses and grounds are in working order, at least the ones I could find, hopefully there aren't any more. I got a 12v relay to do the mod in the next days.

I'm about ready to just drive it like that and stop careing about that stupid LP:mad:
You need that LP,Dont leave home without it or IP will be next to crap out.

Did you check the fuse next to the LP relay on the firewall?

oh yes I know the importance of the LP... it's just so frustrating that it works fine and then the next time I start it up everything is gone again!

Could it be that something is killing my OPS's right after I put them in? That fuse next to the LP relay is good, I'm going to do the OPS relay mod now and then see what happens :)

I am not sure if yours is so equipped as mine, however, there is a ground on the frame rail right behind (towards the rear of my frame rail) from the LP. If yours is wired alike, That is a ground for my LP, which would be needing good metal to metal grounding. It is about 6 to 10 inches towards the rear tires from the LP. (Never know it might solve lots)

Thanks a lot, that should hopefully solve my issues, I noticed the cable going to the back but never actually looked, I'll check that out asap! :)

Yessss, the LP is running!! :)

I checked that ground wire from the LP and it ended in a real dump place next to the tank, so I cut it and grounded it somewhere else on the frame, then I twisted the cable and through pure luck found that someone had just twist tied the cable together at one point and shrink wrapped it!!!! So I fixed that and now it's purring like a kitten:D !!!

Thanks again to everyone.