thunderstick

ok - lit off my new engine last sunday and again last night just playing around for now, but in the interim of rebuilding, all i did to any wiring was relocate (reroute) the fan wires and the starter harness - that's it. i attached my alarm hot wire to the hot wire on the alternator (coming off battery) and that is the only "change" i made. now, with the key "on", it sounds like the alternator is "on", like it's doing something inside - sounds like a medium pitch humming. i disconnected the plug on top that goes to the gauge and somewhere else, and it doesn't do it. never did that before, don't know what's causing it. that's one gremlin. the other is that with the key on also, if i turn my lights on, the fuel pump cycles on. pull it once more for headlights, and it cycles again. turn the fogs on, it cycles. key still on, hold the brake, cycles on. put the shifter in reverse, it cycles again. WTF??? never saw anything like that. i hope someone can help, cuz i'm clueless. i was very careful when working with any of my wiring, but things can happen. i just don't know what did. i took out the relay to the f/p and it wouldn't do it then, also swapped it with another i had, and it still did it then. HELP...

KAM

JeffW

bad ground..... did you install your ground straps on the rear of the heads? for the fuel pump gremlin you are feeding power into the chasiss some how check your grounds carefully, i would expect all gremlins are related.

jeff

thunderstick

that's kinda what i was thinking, too. yes, grounds are hooked up, but am gonna double check tomorrow. couldn't get to it today (honey-do list, you know). thanks for the reply. hopefully it's that simple...

KAM

Vader

Since you're evidently still having trouble with this, over a year later, it's time for a revival.

If you can, pull all the information from other forums into this thread, or at least provide links, so that we're all on the same page (pages?). Here is what I found via a quick search:

https://www.thirdgen.org/techbb2/sho...hreadid=159565

https://www.thirdgen.org/techbb2/sho...hreadid=296357

https://www.thirdgen.org/techbb2/sho...hreadid=299131

https://www.thirdgen.org/techbb2/sho...hreadid=299267

https://www.thirdgen.org/techbb2/sho...hreadid=302595

https://www.thirdgen.org/techbb2/sho...hreadid=318921

https://www.thirdgen.org/techbb2/sho...hreadid=334537

https://www.thirdgen.org/techbb2/sho...hreadid=332144

Perhaps pulling together all the relevant information would help, too.

Or, do you have a trailer?

Vader

Chronologically, here's what it looks like:

'91 w/L98... is the fuel pump (relay) located on the firewall with the fan relays? I can't remember, but thinking I知 gonna have to change it, because the pump runs intermittently when i shut the engine off, instead of running steady before it shuts off completely...

OK - I replaced the relay... next question I have is... when the engine is shut off, is the pump supposed to run for a few seconds or shut off upon engine shutdown? This is similar to the issue I started with, meaning that now when I shut the engine off, the pump shuts off. Before when I shut it down, the pump still ran for a few seconds, but was intermittent. On my IROC, the pump on it runs for a few seconds after shutdown, so... with this new relay in my '91, it shuts off when I shut the engine down...

the amount of time the pump runs has cut down drastically since i changed the relay, but now i知 thinking my '90 IROC has the same problem because it runs a considerable amount of time after engine shut down. i thought before that the reason the pump continued to run after shut down was to maintain pressure on the system, whatever purpose that may serve, because like as you say, when the key is turned on, the pump primes up the system. now on my IROC, it runs with high oil pressure constantly when the engine is on, so that switch may be causing that issue. I値l have to really take a look at both cars and compare notes. thanks for your responses...

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

as it says, i知 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知 not an electrical genius, but know some basic stuff, so i知 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致e 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...

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?

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知 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...

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知 all ears for any more help.

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?

well that hope was short lived, and i guess i should have 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 don稚 know 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...

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 received by the ECM (from cranking or running). "

so... with that in mind, it probably isn't a bad ground after all. sounds like the ignition module is sending the signal to the eCM even though the eng is not running. i致e 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...

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, because it was your post on another thread that more or less confirmed what i was suspecting when i narrowed it down to the module.

well, scratch every thing i just said, because 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 old' 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, let me know - especially about the pick-up coil/pulse thing...

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?

oh damn well - back to the drawing board... got my new pick-up coil today and put it in and same old' 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?

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.

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, because that's what signals that when the key is initially turned on. that is the problem i知 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?

Vader

...And the rest:

on my '91, i believe the eCM is a 7730... anyways, i need to verify if pin "D1" is supposed to be a ground. (blk/wht wire) i致e been chasing a gremlin for a while, and decided to try reading at the eCM (since it is cycling the fuel pump with the lights, key on). i know the black/white wires are grounds, but don't know if all of them are. this one reads .06 V with key off, 9.07 V with key on, then jumps to about 9.7+ V if i hit the lights. i can chase the wire down, but if anyone can verify that wire for me, I壇 appreciate it... i知 going to go try to locate it under the hood in the meantime... thanks.

thanks, trickster. you probably remember this one from last weekend... still working on it. but i have made another discovery. in addition to that D1 pin having 9+ volts when power is applied, so does the ground on the a/c pressure switch, and (drum roll, please) so does the fuel pump relay ground. imagine that. one of the grounds on the back of the head is also showing the voltage, but not the one with the tan wire. it is one with two of the blk/wht wires. right now i知 pulling up the wire bundle and physically tracing the wires down to a common joint, but that'll probably take me back somewhere else... anyways, the voltage shows at all points mentioned with them all disconnected from their respective component. man, this really sucks...

ok - i pulled up the wire bundle(s) with the suspect "hot" grounds and narrowed it down to one of the wires going in to the car (ugh!) it was attached to the lug at the back of the head, so i traced all wires attached going both directions, and unfortunately, two of them go into the cabin... so i decided to isolate it if possible, and cut one of the two wires attached to the lug, and that isolated it somewhat. both of the wires in question go thru that big connector looking thing at the firewall. both of the wires read 0 volts with the key off, but with key on, one reads 9+ volts, the other 5+ volts. IF the eCM is all connected, that same wire will read less than 1 volt, but still has a trace. tomorrow i知 going to try again to isolate the source by pulling fuses one at a time, but that didn't seem to work today. any help will be appreciated... thanks.

in my quest to figure out this gremlin i have, i did find two hot grounds yesterday. when i asked about the D1 pin on the eCM being a ground, trickster verified that for me, so i physically traced all that wire and different connection points. it was originally attached to the rear of the left head with another wire, which when separated, both read hot with the key on. the one that goes to D1 is actually only reading 5.3 volts, the other is reading 9+ volts. that one (9+) goes in to the cabin by the brake master cylinder, but haven't found out where yet, other than it also reads the same at the SIR relay like thing on the left firewall. i know the source it's coming from is inside the car, because i致e clipped the wire where it was attached to the head. the other one (5.3v) also goes in to the cabin, but i have not isolated it yet to the source coming from inside the car. anyhow, both of these grounds read 0 volts with key OFF, then 9v and 5V with key ON.

the voltage is "active" with the known components disconnected. i知 trying to pin-point the source by removing all known hot grounds. the one wire that goes to the D1 pin on the eCM is also spliced to the a/c lo press switch and fuel pump relay, if i recall correctly. i can't verify that for certain right now because i am out of town, but i think that's how it goes. regardless, with all of those plugs disconnected from their respective components, the voltage is still there. the other wire that has not been isolated yet may be the actual culprit going in to the cabin and affecting the other one coming out, i don't know. this whole thing has something to do with the lights - any lights in the marker/head/fog lights and/or brakes.

here's another scenario: with the key ON, there is a high-pitch hum coming from the alternator (volt reg?). when i pull the light switch to park and/or head, that hum goes away. if i disconnect that connector, that hum is no longer there, but voltage is still present at those grounds.

and yet another scenario: when i reattach the neg cable to battery, key in OFF, the marker lights would come on dimly and i could hear a popping (like a relay click) inside the car. lights would stay on for a couple of seconds and go out. i disconnected what i think is the fog light relay and the popping went away, BUT now the lights will stay on at all times. so, i have to have my batt disconnected right now... i知 not 100% sure it was the fog lite relay i disconnected because of the wiring colors, but that stopped the popping i had. (wires were blue, green, brown, and a tan) and it is mounted behind the turn signal flasher under the column.

BTW, i tried to single out the source by pulling fuses one at a time, with no real joy. if i pull the SIR and GAUGES, the voltage will go away, but not completely by one or the other - has to be both.

i have two grounds reading voltage, one is 5+ volts, the other is 10+ volts. one is definitely coming from inside the car, and i suspect the other is, too. but someone expound on this issue because i知 thinking there should be no voltage on a ground what-so-ever. so if this is right, then i need to start searching for the culprit(s) that are causing the problem. and bTW, the grounds only become "hot" when the key is turned on...

the connections are all good. something somewhere is causing this situation - a sensor or something. could even be the gauge cluster, since it's on the same ground system. not all systems are reading a voltage, so if there was only one ground, then everything would have voltage, i would think.

one of the "hot" grounds is the one coming thru pin "F8" and if i recall, that is the one getting 10+. the other is coming thru pin "C7", and that is getting 5+. that voltage is present with the eCM, fp relay, and the ac press switch all disconnected. both of these grounds connect at G112, and these two were coupled together. (they are separated at the moment) the other coupled grounds are the O2 (tan) and D1, i believe. (i don't have them in front of me), but they are apparently getting "0" volts. now if i couple all of those grounds back together, the volts at G112 go down to like .05V, but the fuel pump cycle with the lights is still there.

apparently the fault is inside somewhere. i致e been over and over and back over everything i did, and cannot find a disconnected ground. the harness stayed in the car during the rebuild and i was very careful whenever i moved it. everything works, nothing shorts or blows fuses. the different voltages make no sense, either. i hear what you're saying about them not being connected and definitely not being grounded, but i cannot figure out where.

the only other two grounds that weren't on the schematics trickster sent me were to the cooling fans (which hook up at the same location as the pigtail off the neg batt cable, and another small 2-wire one that is attached at the firewall by the relays on the driver's side... but they are in the same place as they were before, so...

i only can work on it on weekends, so time is limited. regardless, i still can't determine what the problem is, but on the other side of the coin, i don't want to have to pay a lot of $ for a shop to find and fix, either. may have to do that, though. i致e already got half the harness open up anyways, so a little more certainly ain't a big deal. i just don't understand how supposedly everything can be grounded and get a hot wire. i think that ground going thru F8 and C7 should be going IN to the car to those components, not reading hot on the back side.

those pins are in the C100 connector. both are grounds, going from the head TO the inside of the car. i was just reading a post by sonix that had a similar problem with his CTSY lights, and if i understood it correctly, it was caused by a fuse that looked good, but didn't function good... it seems odd that the problem is originating from inside the car when nothing in there was ever disturbed, so a faulty fuse? maybe... i guess i値l replace every one with a fresh one and other than that, open up every inch of harness that i had open when i did the rebuild and inspect every wire and terminal - and clean (again) every single grounding point whether i disturbed it or not.

where is the passkey decoder module?

and what does it look like? it may or may not be the key to my problem, but i have a very high resistance on that indicator terminal at my inst. panel connector, also on my infl rest indicator terminal. all i see behind the inst panel where it supposedly should be is a kinda' flat black box looking thing, about 4" X 6", mounted near the heater core cover, but the wiring doesn't seem to match what the book says should be there. and even with that disconnected, the high resistance is still there. if you have a pic of what it looks like, that would help. this is for my 91 Z 5.7 TPI (VIN 8).

yea, i知 still chasing this SOB.. gave it up for a month or so. two different ground circuits, as you know. the security indicator has lots of resistance to ground and so does the infl rest. the airbag system seems to check out alright, though. does the self test and goes back out. the security light does not come on, but that is probably because i did have that module disconnected. so tomorrow i will hook it back up and check it again, but why would there be such high resistance on those two circuits? if i check those grounds to each other, there is 48 ohms resistance. if i check the security terminal to ground, it is 1000+ ohms, can't remember what the infl rest terminal was, but it was way up there, too. the passkey decoder module seems to be a common thing because it's on the one ground (450) but there are wires to the gages fuse and at the fuse block, that is coupled to the SIR fuse as far as power distribution when the key is on. i had thought before that the DERM for the SIR system was the culprit, but doesn't seem to be. if i disconnect it AND the arming sensor, that ground (1003) issue goes away. if i pull the gages AND SIR fuse, it goes away. if i pull the ECM fuse, the other ground (450) issue goes away.

OK. Is it possible for those two grounds to show voltage in them because maybe they weren't grounded where they should be very well? one reason i知 asking is because when i reconnected the 1003 ground back up, the voltage disappeared and read almost zero. and it probably read that little bit because the jumper wire it was attached to didn't have the best connection. and i assume that because the other wires read out good up to that point. but it is a temporary jumper for trouble shooting. i will reconnect the other ground (450) today and see if it goes to zero, as well. and if that's the case, then maybe my suspected problem never really existed? Maybe it was crappy connections all along? The only other thing in the list of it all is if my fuel pump still primes with the lights being turned on... i have a lot of things to hook back up to verify that, though. there was another guy who experienced that same thing a couple of months ago and i talked to him last week - his problem just went away on its own. before i started tearing in to all this, everything seemed to work as advertised - no codes, either. only thing out of the ordinary was the excessive fuel consumption, but that could be from the AFPR i put on and/or needing another prom burnt for my cam.

dare i ask how? and with all the "troubleshooting" i致e been doing, whether it be right or wrong, there's a good chance i boinked something up along the way...

posted this in electronics way back when with really no informative response, but maybe someone here that knows ECM's and their circuitry might be able to help... the vehicle i知 referring to is my '91 5.7L TPI.

problem = with key in the "ON" position, fuel pump cycles for 2 seconds like it's supposed to. if i pull the headlight switch, or hit the brakes, fuel pump will cycle again like it's NOT supposed to. this gremlin was discovered after a rebuild almost a year ago, but have been doing other things to the car in the meantime. the only info i can add to the troubleshooting is that if i disconnect either connector on the (remote) coil, it will not do it. so i supplied power direct from battery to coil for it's power supply, and it still did it. i have also replaced the ignition module and pick-up coil in the distributor, both to no avail. i understand the fuel pump is powered by the eCM when it receives the signal from the dist, and is also wired to the oil pressure switch. i知 not clear as to which way the current flows on any of it, but have a digital VOM to chase wires with. i just don't want to chase my tail with this. it really isn't much of a problem, but it isn't right that it is doing it, besides being annoying. i don't know where the ECM could be getting another input signal from to cycle the pump...

a little more playing around with it yesterday and now it doesn't cycle with the brakes, but will with the back-up lights. according to my diagrams, the light switch and the reverse lights are on circuit #150, eCM is on #450, and a common connection point is the back of the pass head at G118. those grounds were repaired but i think the stud itself on the back of the head may be a problem, so gonna start there with it. easy enough to get to, but not as easy as the other head... once i disconnect it, i値l check the wiring for continuity. gonna check out the ref low wire, too. i値l post with results, and hopefully will have them today or tomorrow.

RBob, disconnected the grounds from G118 and attached (jumpered) them directly to the battery neg post. still got the pump w/lights. checked those same wires to the connector at the eCM (D7 and A12), got .2 ohm. checked all wires for ignition module to eCM (D7,D8,C7,C8) and all read about .2 ohm also. i was sure i had checked these way back when, but easy enough to check again. continuity for ground seems to be good from battery through the block. i didn't check G112 again (but will) because i had a problem there before and had to clean that all up. i realize the eCM is grounded there also, but the symptoms i had with that ground before appear to be corrected now. one last note is that when i check my DVM leads, i get .2 ohm there, as well, so all the readings i get seem to be "solid". any more ideas or direction? i知 heading back out to clean the actual body parts where the light grounds go to, but they also didn't seem to yield any problems when i jumpered those, either...

thunderstick

wow, vader... i hope you don't hate me when i say i found the problem today... it is the fuel pump and/or wiring to it between the connector and pump itself. verified, too. i posted this on the ecm board, as well, after you had posted. i almost feel like a super-hero now. wish i had the strength of one so i wouldn't have to drain a FULL f'ing tank of gas!!!