Ive got kind of a bizarre problem here, but Im not sure if its several different issues are one big related problem.

The car will not idle, the only way to keep the engine running is to tap the throttle lightly. The engine sputters and backfires through the intake and just runs horribly.

I found that the FP/inj.2 fuse (in the interior fuse block) was blown, but I could still make the car run, and it had 45 psi of fuel pressure. I noticed now that the pump primes normally when you turn the key on, but it will also prime again if you turn the headlights or the domelight on (using the switch or opening the door).

Has anyone else had a problem like this? Any ideas?

 

Also, depressing the brake pedal will cause the pump to prime, as will moving the shifter to reverse.

I cannot find anything in the wiring diagram that these circuits have in common except the fusebox.

Any ideas?

 

HELL YES! i thought i was a one-of-a-kind of guy... i have that same problem and have been trying to find the cause of it for MONTHS now, and am still working on it! i did a rebuild not too long ago, made a few wiring mods (basically relocating), but was very **** and careful with the wiring. got it all back together and it does exactly what you are saying. i cannot figure it out, either. i have my car torn all apart now, but that was pretty much a waste of time, too. problem still exists. i even replaced the ecm because the fuel pump switch is in there, but no joy... sorry i can't really help you, but finally - misery loves company. welcome to my world...

also, in my travels to find this problem, i cleaned and checked all my grounds and all my fuses - no joy. i did, however, find that two grounds that attach to the back of the driver side head were showing some voltage in them, so i cut them to isolate them, but... no joy.

 

Well at least Im not alone in my problems.

Doesnt seem like anyone has any ideas though.

 

yea, you ain't lying about that one... i think next week when i get home i'm gonna go by this one automotive electrical repair place and see if they have any ideas. but, not wishing anything bad on ya, but i'm glad you posted with the same problem, cuz i thought mine was caused by me somehow and that's why i've been tearing the car apart looking for it. nothing has been obvious, i've even put things back the way they were, but all to no avail. a couple of guys have helped me out with grounding issues, but it's all come up empty. i'm kinda' at the point of not knowing what else to do, so the car is just sitting there with a brand new engine and trans waiting to be broken in...

 

I admit you have quite a unique & confusing problem. Quite frankly, I haven't any ideas but I do have a few questions...

Does the pump actually just prime (standard 2 seconds & stop) or will it run for the duration of one of your described events (ie: run until you close the door, etc) ?

Will the problem occur if the FP relay is unplugged ?

Will the problem occur if the FP switch (above oil filter, 2wire, 3wire later years) is unplugged, relay plugged in ?

Will the problem occur if the ECM fuse is pulled (weatherpack by the battery) ?

Does the problem happen only when the key is in the 'run' position of when it's off as well ?

(by listening while another person creats the problem) Is the relay actually switching ?

The confusing part is the dome lights work by completing the circuit through ground... the other by +12v.

Is there any useful background that led up to this problem ?

 

Has this problem existed for awhile or has it just popped up suddenly. And if it has jus just popped up suddenly, was there anything that you might have changed that could affect it? The only thing all your affected systems have in common is the grounds and Thunderstick has been fighting this problem for awhile now.

 

Yeah, the pump just primes. The key has to be in the 'run' position for any of this to happen, it will not prime at all with the relay removed. The relay does click when the pump primes. I havent tried unhooking the oil press. switch yet.

The problem occured after I retorqued my headgaskets (which involved removing the headers and rockers), and installed a new O2 sensor. This may seem odd, but the problem seemed to get progressively worse. I took the car out and drove it, and it refused to rev past 3000 rpm, it just cut out and sputtered badly. I drove it home and tried it a few hours later, at which point the car wouldnt idle at all, and the only way to make it run is to repeatedly tap the gas. It backfires through the intake badly when I can actually get the engine to rev up in park.

Thanks for the help guys.

Thuderstick, does your car run at all?

 

Since you removed and replaced the headers and rockers, did you reconnect all the ground wires at the back of the cylinder heads. That is where the ground wires that I mentioned earlier connect to.

 

Yeah, I actually didnt disconnect them when I worked on the car. But I did check to make sure, they appear to be ok.

 

yes, it used to, meaning that if i hook everything i have all torn apart, i'm sure it will run again. before i started tearing it all apart in an effort to t'shoot this, it ran great. i wouldn't even know the issue existed if i hadn't stumbled across it. i have a couple of other issues, too, but they may be related to this same problem, i don't know yet. but those issues are electrical, too, not mechanical. overall, it was running great.

to answer some of deadbird's ?'s, the signal to prime the pump will still be there at the relay connector with the relay removed. test light shows that. it will still do it when the oil press switch is disconnected. haven't tried with the fuse removed, as i believe it goes to the pump, as well. i'll have to try that next time. i don't think that will help because if that fuse also goes to the ecm, the signal to cycle the pump comes from the ecm, so removing power to it would keep it from priming even initially by turning the key on. right? one thing myself and formularpm don't have in common is that apparently his car does it with the domelight also. i don't think mine does, or at least haven't noticed it. i did get it to do it once when hitting the right blinker...

one thing i did notice on mine is that i mentioned a couple of grounds having voltage in them and the rheostat in the headlight switch seems to affect that. but i also removed the headlight switch and the pump still will cycle when hitting brakes.

 

Yeah, when the domelight comes on, it primes. Doesnt matter if I use the switch or just open the door.

Now Im wondering if my runability problem and this problem are even related...

 

The answers help eleminate a good part of the problem as far as power leeching through the system/wiring.

I'm no ECM expert at all but, from the sounds of things.. it seems as though the short (hunt for ground?) is causing a false tach signal to the ignition module somehow.
That is the only thing I can come up with. If the ECM 'sees' any kind of pulse from the distributor, it will start running the pump. If it's just a single pules, the pump will run just briefly.
I've come across this while f'n w/the distributor & having the key on. Turn the distributor enough for it get a pulse and the pump will prime. Same thing applies to furds (just help fix friends van.. key on, turn the dizz and the hall effect made a pulse.. pump primed).

Lackluster and way far out in left field answer I know but, that's the only thing I can come up with. If the pump were just flat out running.. I'd think otherwise.

 

yea, that's something else i coulda' added to my post... in my t/shooting, i noticed that if i disconnected either one of the plugs on the ignition module, the prime stopped. thought i found the problem, figured it was a bad module and swapped in a spare i had. no joy. so then i thought pick-up coil (MSD dist, easy to change), so i changed that. no joy. i thought the same thing, though, that the ecm was seeing a pulse from the dist and priming the pump. with the tach in the cluster, i also found that by pulling the fuse for the gauges AND the SIR, my "hot" grounds go away. i didn't notice if by pulling those two fuses if my prime stops, though. i'd have to check that. but both fuses have to come out, not just one or the other... also, i removed my cluster and headlight switch in this process - still primes... i also had changed my ignition coil, but not because of this, so i suppose that eliminates that as a possibility, too.

 

any new developments with this? i can only work on mine during the weekends, but this weekend probably won't be one of them... seems to be tach/dist/ign module related.

 

No, Im in the same situation as you. Im at college, and my car is like 200 miles away.

I do have an aftermarket tach, I disconnected the power source from it to see if it made a difference, no dice. Are you just using the factory tach or an aftermarket?

I also swapped to a known good (stock) ign. module, but that made no difference. My distributor is a brand new MSD, I know that doesnt mean it couldnt be the problem, but I think its unlikely.

 

i'm using stock tach, also MSD dist. i think your dist is highly unlikely to be causing it, too. i e-mailed gm to see if their tech guru's can help or will even respond. i'm not too sure if my "hot" grounds are even related to this, but it would be nice so that both issues are resolved at the same time. with the strange way that electricity acts in a car and my limited amount of knowledge on the subject, i'm not even sure if my other grounds are good, even though i think they are...

 

Hot physically? I noticed that the ground terminal on the battery seems to get very hot (when I can actually get the car to run).

 

no, when i turn the key on, they get voltage to them. one is like 5+ volts, the other is like 10+ volts. but i think the cause is in the cabin somewhere, as i have clipped those wires going to the grounds in the engine bay to determine which side they were on, and they're hot on the cabin side. but... that's not to say they are getting their source from somewhere else, going thru that main connector and coming back out. who the hell knows? if i understood this stuff better, i would. but i don't so i can only guess. if i get an answer back from gm, then i will hit them up with that one, too.

 

well i actually got a response back from gm, but don't think they're gonna be able to help me via e-mail or phone, judging from the jist of the response i received. but, they are supposed to call me tonight, so i will post with the results...

 

That would suggest (to me) that there is current bleeding into the ignition wiring and the ECM is 'seeing' a tach pulse (not the one that the gauge reads from the coil). The module is the completion of the circuit (when plugged in).

Hard to say though w/o personally digging through wiring.

To add to the oddities... I had a remotely similar problem when I finally got my 'bird up and running. I never had the prime problem but, if the prking lamps or headlamps were on, the car would run like complete poo. Gagues would act up when the turn signal was on and the flash was snail with vertigo slow. Looked and tested, probed, test, look... came down to the headlamp grounds (on the rad support) were bad/loose (from painting the engine bay. Oddly, this caused a horrid running problem (signals/lamps were chasing back through critical wiring to find ground).

May seem totally irrelevant but, make sure all groundsw are good. After my exp.. I bought a 2ga battery ground, have a 8ga batt to chassis ground and a 4ga block to chassis ground.

Sometimes the simplest things can cause huge problems.

Not a solution but, just food for thought.

 

i had done some touch-up painting, too, and that was the first thing i went for. cleaned up all the ground terminals and frame where they attached. no joy... only thing i couldn't really go back and do over were the ground studs on the back of the heads. when i put them in, the heads were painted, and i installed them with lock-tite. however, the ground seems to check good thru the block and i have jumpers on every thing that attaches to those grounds right now anyways, so i think those studs are still ok.

i got my helms book yesterday and already glad i bought it. i'll probably be forever reading thru it, but at least it tells you damn near everything you need to know. my phone conversation with gm last night was pretty much worthless, as expected. i'll do some more t/shooting if i get a chance this weekend, but just looking thru the book has already given me some more insight to the wiring system overall.

 

Ive *casually* checked all of the grounds that I could find, unfortunately the Chiltons wiring diagrams leave a lot to be desired, including ground locations. I need to check the continuity of the grounds yet.

I agree that faulty grounds likely have some part in this mess. I just cant fathom why else so many, seemingly independent circuits would affect one another. I still dont understand why the battery ground terminal would get so ridiculously hot.

Good idea.

Yeah I have serious runability problems, I was hoping that they had at least something to do with the superfluous prime situation. Makes sense that grounding for other circuits may be backtracking through power for others, but I still dont understand the domelight... So, what were your runability symptoms, deadbird?

 

formularpm, are you getting any "hot" grounds, that you know of? particularly on the pump relay socket, maybe the lo press a/c switch near the a/c drier? (need to check with the key on) if you read voltage from the batt negative terminal to the blk/wht wire of either one of those connectors? just curious, because browsing thru my book last night, the ground for the tach is on that same system, which i didn't know before.

i also think that the "DERM" may be the culprit of my hot ground for at least one, anyways, because it is linked to the SIR, gages, and crk - all of which read continuity to ground...