this is for my '91 5.7L TPI... (L98)

as it says, i'm still looking for this bad ground and cannot seem to find it. it "appears" to be one of the grounds on the back of the driver side head. there are 4 grounds there, 3 are b/w wires, the other is a tan. i'm not an electrical genius, but know some basic stuff, so i'm obviously missing something... anyways, this ground causes the ecm to signal the fuel pump with the key in the on position and turning on any lights - headlights, brakes, etc. it appears that all 4 of those grounds go to the ecm. in my book, it shows 2 of the b/w grounding at one point, and the other b/w and tan grounding to another point - with the braided bonding wire. it was not like that when i removed the engine for the rebuild, so did not put it back together as such. when i isolate the two grounds, it seems to offer more resistance with the tan and b/w ground (1.6+ ohm) than with the other ground (about .4 ohm). i was told if it was a break in one of the wires, it would read infinite, so before i go pulling a harness out to search for probable cause, does anyone have any other ideas for trouble shooting? i took it to a "reputable" shop that has done other repairs on my vehicles and they said the same thing - found high resistance on that one ground. after talking to them again, the also mentioned that they found that high resistance up at the aldl connector also. they said it was a bad connector on the back of the head, repaired it and sent me on my way. well, it ain't fixed...

also, on the fuel pump relay, according to my book, that wiring is all wrong and colors don't even match. but that, too, is the way it was before, so am not about to go there. also, where does the pump receive it's power from? the relay, once the circuit is complete?

this is like the 3rd or 4th time i've really gotten in to trying to fix this thing, and i replaced the ecm the second time because we thought it was the switch inside it that energizes the fuel pump.

please help if you can, with troubleshooting help or anything. this is driving me nuts and i want the car to run right. still got a couple of issues, but right now, this is the main one and i want it fixed without paying a couple of hundred $ again for nothing...

KAM

 

Hello Thunderstick,

Yes there are supposed to be four (4) ground wires on the back of the left cylinder head and one of them is a "TAN" wire. It goes to pin "E15" on the ECM and is the ground for the Oxygen (O2) sensor. The wiring for the fuel pump relay on your car is as follows.

Pin "A" = orange wire (power)
Pin "B" = no wire
Pin "C" = red wire (diagnostic test point)
Pin "D" = dark green/white wire (fuel pump relay driver at ECM)
Pin "E" = gray wire (fuel pump signal voltage monitor at ECM)
Pin "F" = black/white wire (ground)

This info is from the 91 camaro service manual.

 

thanks, trickster...

well, the relay connector is wired correctly, as per your feedback. i don't understand the ground wire for the O2, though. i thought the ground for that was picked up via the manifold (or headers). as of right now, the tan wire and the other b/w wire are still coupled together on the same lug, and i don't want to have to separate them again, but even if i take the O2 out of the bung, the resistance is still there. if i run a pigtail directly to the O2 for a ground, still the same result. the resistance is measuring about 2.4 - 2.7 ohm. if a ground is "good", shouldn't it read less than .5 ohm?

 

You should be checking it for voltage, not OHM's. It should be reading "0" volts with the key in either the "ON" or "OFF" position.

 

well here's an interesting discovery... i was getting minute voltage from the ground wire at the f/p relay (.09V) when i applied any lights, it would go to .12V. then i noticed i heard a "click" near the distributor area any time any kind of lights were applied. couldn't pin-point it, so started chasing the ground wire in question. started taking things out of my way, and found that when the 4-PIN connector on the distributor is disconnected, all works as advertised in reference to the fuel pump. it cycles on with key turned on, and that's it. no more cycles when any lights are applied.

so... where do those 4 wires go? i'm thinking i have a bad ignition module, but it's an MSD, so don't know if it can be tested anywhere or not. i looked at the colors of wire on that connector, but none seem to be related to the f/p relay - apparently the module is sending erroneous crap to the ecm? i suppose, too, if it is a bad module that it's been part of my "gas mileage" issue? it seems to have crashed to next to nothing since i rebuilt, and i don't see the upgrades having that significant of an impact on it...

 

Here is the color coding and routing of that four pin connector that goes to the distributor.

Pin "A" = black/red wire ground to pin "D9" of ECM
Pin "B" = tan/black wire set timing connector
Pin "C" = purple/white wire pulse reference to ECM
Pin "D" = white wire to pin "C8" at ECM for Electronic Spark timing (EST)

Hope this helps some

 

thanks again. answers my ? of where they go, but upon even further review, seems as though if either connector are disconnected from that module, the issue goes away. i reconnected the 4-pin and disconnected the 2-pin. i had a spare ign coil, but didn't seem to be the issue. and as far as the module goes, the engine will runs very good. i just don't see how this problem can pass through the distributor, other than it and the pump are tied in to the ecm. the blk/red wire being a ground may be an issue, but still makes no sense to me, other than maybe the wires are shorted together somewhere, but i think that's pretty unlikely... and as mentioned, already changed out the ecm, so... i'm all ears for any more help.

KAM

trickster, you say that blk/red is a ground to ecm? it's reading .98 volt, and i cannot get any continuity out of it. can't measure and can't even get the dummy "beep", so sounds to me like it's a broken wire??? agree? but once again, just curious as to how that would affect the ignition / timing / fuel economy?

KAM

 

well that hope was short lived, and i guess i shoulda' been more specific anyways... when i tried to read continuity, i was reading from the pin on the dist. connector to a ground on the block. no beep, no nothing, but i got .98 volt. when i went to the other end of the wire at the ecm connector, wire checked good. so i dunno wtf... if i don't have a broken wire, i don't know what to fix. all i know is that if either one of those connectors are removed from the ign module, problem goes away...

KAM

 

Sorry I goofed on that pin location for the black/red wire in that last post. It should have been pin "D9" instead of pin "B9". I have already made the changes in my last post. The voltage reading should be "0" with key on or off. Also the first picture that I looked at showed it as a ground, it is also the pulse reference signal (LO) from the distributor. Pin "C" is the pulse reference signal (HI) from the distributor.

 

thanks again, trickster... i was searching some other forums and found an interesting response on one that says:

"And incidentally, the prime cycle is two seconds after the ignition is first turned on. The prime cycle will not repeat until either the ignition is turned off for at least 20 seconds, or the distributor reference pulse signal is recieved by the ECM (from cranking or running). "

so... with that in mind, it probably isn't a bad ground afterall. sounds like the ignition module is sending the signal to the ecm even though the eng is not running. i've got a spare gm module, i think, and am gonna slave it in and see if it rectifies the problem, but that's what it sounds like... wish me luck

 

well, looks like the ecm was getting a constant reference pulse from the ignition module... i read voltage coming to that 4-pin connector to make sure the signal wasn't coming from one of those other sources and going thru the module back to the ecm, and all checked good. then i read voltage from the 2-pin connector to make sure it wasn't coming from there, either. so then i slaved in my spare gm module and hooked it all up, and life is good! now i just have to get a new module for the (MSD) distributor...

trickster, thanks very much for your help. you, too, vader, if you're reading this, cuz it was your post on another thread that more or less confirmed what i was suspecting when i narrowed it down to the module.

KAM

 

well, scratch every thing i just said, cuz it's all back - same as before... for one thing, MSD uses GM modules just in case anybody such as myself didn't already know that. so i had a spare GM module (known to be good last use) and when i "slaved" it in and hooked it up, everything worked as advertised. life was good. so, i start wrapping the harnesses back up, putting every thing back together thinking everything was good. then i took the old module out of the distributor, put the other one (permanent install) in and we're back to the same ol' crap... but once again, if i disconnect the dist. connectors, the problem goes away. so... the only difference i can think of between the dummy install and the permanent install is that there was no pick-up coil hooked up when i did the dummy install. which brings up the next question - is the "pulse" signal received from the pick-up coil? i guess i need to make a jumper to troubleshoot it, but damn if this ain't getting old... i guess this is more or less another update, but if anyone knows anything else to add, lemme know - especially about the pick-up coil/pulse thing...

KAM

 

Yes. the pickup coil is what creates the pulses for the ignition module when the reluctor is spinning past the pick-up poles on the distributor.

 

ok - well, this is what i did this time... i "slaved" up the original module, since it was apparently good, by connecting the two connectors and a brand new GM pick-up coil i just happened to have, put a little jumper wire on the module for ground (just in case it has to have one) and it checked good. luckily the MSD coils are a screw-on type and i won't have to pull the dist to change it. just ordered a new one, but another question i have is would corrosion, such as a rust type, on the reluctor cause a funked out pulse to make it think it's running? i don't see how, but... never thought a coil could cause this kind of problem, either, but i feel confident it will fix it. any thoughts on it?

 

I don't know about all distributors, but the distributor in my car when I first got it had so much corrosion in it that there was hardly any gap between the poles and the reluctor. BTW, the ignition module is grounded to the base of the distributor by the metal plate on the back of it. Also don't forget to put a good coating of di-electric grease on that metal plate or it will cook in a heartbeat.

 

oh damn well - back to the drawing board... got my new pick-up coil today and put it in and same ol' crap prevails... i don't get it... disconnect the connectors to the distributor and the problem goes away. changed the module and the coil and still have it... any other ideas??? anyone?

 

Okay,
Just for curiousity's sake, you keep mentioning that you have disconnected the connectors at the distributor. Exactly which one (or ones) did you disconnect? BTW, one thing that I just happened to think of. Please check the two wire connector at the back of the distributor and make sure that you didn't connect the MAT sensor to the ignition module instead of the ignition coil. This has been know to happen on rare occassions since the connectors are the same.

 

both connectors - the 4-pin one (that's the one you gave me the pin info on in a previous post), and the 2-pin that connects to the coil, has a pink and white wire, i think pink is the power and white is for tach. no, i did not hook the mat to the coil, but seen it happen before, too, but thanks for asking about the possibility. if i disconnect either connector (one at a time) the problem goes away. i also checked for voltage coming thru that 4-pin that was maybe coming in from somewhere, going thru the module, and back to the ecm, but there were no "spikes". all read "0". the lights that affect it are the park/dash lights, headlights, fog lights, and brakes. turn signals, rear hatch defrost, heat/ac, interior lights do NOT affect it. at one time i thought when i put the shifter in reverse it was doing it, but i just checked it, and seemed to be ok.

 

Are you saying now that the lights are having an effect on your problem?

 

no - repeating myself from the original post. meaning that with the key on, if i turn on any of the afore mentioned lights, that is what causes the ecm (or something) to signal that 2-second cycle to the pump. has to be the ecm, cuz that's what signals that when the key is initially turned on. that is the problem i'm trying to fix. i was just adding to the info that the other lights do not cause the ecm to fire up the pump - just the heads, fogs, and brakes.

 

well, the saga continues... now it also may be draining my battery. while t/shooting this gremlin, i put a meter on the relay to watch for voltage spikes with the lights so as not to kill the battery and pump by cycling it all the time. well, one day earlier this week or last week (can't remember) i had to charge the battery. thursday i replaced that pick-up coil and also ran the engine for a bit and it started up with no problems. today i attempt to start it and no joy - just the "rapid-action clicking" at the solenoid. needless to say, in my disgust with this whole thing, the car still sits where it was...

so, possibly this gremlin is tied in to this now apparent battery drain - any ideas where to start looking?

KAM