SOLVED - bad puc, resistance was good, but a/c volts across the puc connector was reading bad when it was cold outside. (volts were fine when warm, a good puc should fluctuate around .25->.75 a/c Volts)

So this has stumped me for a week now. 87gt V6 w/ 150,000miles. When it doesn't start, the tac will read 0 but the engine will crank - I've also noticed a couple times that the battery gauge was only reading 9 volts. I'm pretty sure it usually reads 12 volts when the engine does start. Yes I've read through all of the ignition trouble shooting threads and I've replaced and cleaned just about everything.

Car now has a new battery, new spark plugs, new spark plug wires, new ignition modual (tried 2, both work), new ignition coil (tried 2, both work), sanded rust off the distributor/ignition coil area/the connectors going to this stuff. I think I also tried leaving the tac filter unplugged too once, but that didn't fix the problem (as i recal). - None of this has fixed the problem.


A week ago sunday, the retaining clip on my pickup coil manages to come loose over a big bump, my car stalls wont restart. Tuesday I take out the distributor and put the pickup coil back into place, and put a new clip on it. Starts right up and after timing the engine, it runs great. Now I have no idea if this has anything to do with my current problem, but either way its one hell of a coincidence.

So tuesday night I drive to a friends at 8pm. When i go to leave at 3:30am wednesday morning it wont start, battery gauge reads like 9V. On the 3rd try it wont even crank and acted just like the battery was dead. So i bring over a big batterycharger put it on engine start mode, and this allows the engine to start cranking again - but it still wont start after ample charging. So I re-seat the two coil and two distributor cap plugs to no avail. Then I take the ignition modual out and put in a spare - starts (tested 2 more times) and I drive home. 4 hours latter on wednesday morning at 7:40am - doesn't start... Then when i get home from work at 4pm I didn't even try starting (dumb me) but i swapped back to the origional ignition modual - still wont start. So I try the spare IM, still wont. So I then clean all the dialectric grease off every plug and the spare IM, and put it all back together - and it starts! Then i pull the spare IM one more time to apply a thin layer of dialectric grease (since u need some there or u fry the IM) and after putting the spare back in it starts up again.

The nxt day, thursday morning at 7am - wont start... I put the battery charger on it till 7:30 - still wont start, I take the charger off, try one more time no luck. I do absolutely nothing else to it, but when I come home at 4pm - starts fine - lol. So I figure battery is on the fritz, and I get a brand new a/c delco one and instal it thursday night, I also installed a new set of fierostore spark plug/ignition wires. Everything was still working. Then I decided to put my origional ignition modual back in to see if that was even a problem - guess it wasn't as it started right up.

Friday i didn't get up till 11am - starts fine and starts latter that night too. Saturday at 7am, starts! I take it to discount tire, they fix a flat tire that I got on friday. When I go to pick it up at noon, I pop the trunk to put in my lug nut key and forget to close it. On the first two tries it didn't start & the tac read 0 like it usually does when it dont start (also i think my gauge read like 9v again...wtf). Then for whatever reason this idea gets in my head that'maybe the trunk sensor is stopping the car from starting since my trunk is open! (LoL, obvously wack logic as it can start w/ the trunk up - duh) well I go close the trunk and rofl - it starts... Works fine the rest of the day and even starts at 6am sunday and runs fine all day. Then monday morning same **** : car wont start but cranks, 0 on the tac, and reads like 9v on the battery gauge (I'm drawing a theory that points to: it reads 12V when its gonna start and 9V when it wont). I hop out of the car, go to school in my dads corvette (yay!) and when I get home at 2pm it starts every time I try it all night. -_-

What in the world is going on? Some evil Gnome trapped in my engine compartment? Maybe a bad battery ground? (a thread that shows the location of all the engine grounds w/ pictures would be nice)

------------------

[This message has been edited by cloaked (edited 09-10-2008).]

I had a somewhat similar experience only mine was more consistant. Car would crank but nor start but only if the temp was below 30 deg. If I jumped it it would start and then would start fine for the rest of the day. Anyway I finally traced it down to a bad ground cable. While cranking my voltage would drop to below 10 volts and my ECM shuts down at 10.5 V hence no spark. (OBD1 SC3800).

Which ground cable was it? I'm hoping its just a bad ground on my car, but I have no idea where all the grounds are, or which one is going bad. (pics would be great, description might work, but i may just go 'huh?' and aks for pics =P)

[This message has been edited by cloaked (edited 09-09-2008).]

Whatever it is its gotta be temperature related. My car was starting fine at 6pm today, then a storm moves in and the temperature drops to 50 degrees and by 11pm it wont start - the battery gauge was at 12V this time tho. Prolly wont start in the morning either, and I'll have to wait for it to warm up.

[This message has been edited by cloaked (edited 09-09-2008).]

check the groand going to the starter and check the ground on the battery areas usually if it gets to rotted around the battery that ground fails i had a similiar issue only mine would fail during the day when the temps were high also caused my (im) too fail and i would stall out and have to wait for 30 to 40 minutes to start and then fail again. there is also a ground coming off the trans(auto) check those it wont hurt to even buy a another ground. there is a thread for this.

If your tach is not registering, you have an ignition problem, bottom line. There are only a few componets that can cause this.

PUC - Pick up coil
ICM - Ignition Module
Tach Filter
A bad ignition coil could plausably cause a no RPM signal, but it would have to fail in a very specific way, and Ive never actually heard of it happening.

Since you have replaced the ICM, and you have a reproducable problem, I would reccomend replacing the PUC, its only $12.

If you want to confirm before replacing parts, there are tests you can do.

First, to test the PUC, simply put a meter on the two wires and crank the engine, you should see low AC voltage, its really all or nothing, so if you see 0, you have a problem, anything much over 0 and it should be good.

Once you have confirmed the PUC is working, then test the ICM, which needs a working PUC to function, so make sure you test that first.

To test the PUC \ ICM, take the 4 wire connector off the ICM, then take both connectors off the ignition coil, jumper the two pink wires together to power the ICM. Probe the white wire going to the ICM. When cranking you should see something.. I have only done this test with an Oscilloscope, so Im not sure what the output should be on a multimeter, it could be any of the following while cranking
Frequency - ~28 hz (anything above 0)
Voltage - you should see a fluctuating value
resistance to ground - you should see it fluctuate

If you have an analog meter, that would work best as its easier to see the needle swinging.

At anyrate, if you wanted to test to see if the PUC\ICM were working, that is the test, it takes everything out of the equation except those two componets.
Also, make sure you have <10 ohms resistance between the distributor and the battery 0 would be optimal. A quick test when it wont start would be to clip a wire to the distributor and attatch that to the battery. If that fixes it, you have a grounding problem.

This has nothing to do with your current problem,but...
I would have to say,with a motor thats has 150,000 miles on it your fuel pump is about to go.


Allso when my headlight gears were going out I had a massive power drain.I could actualley see it on the battery charger gage.I couldnt even charge the battery.But I dont think that has anything to do with your problem because your tac is reading 0.

[This message has been edited by James Bond 007 (edited 09-09-2008).]

I'll try everything you mentioned.

Can I do the puc and icm tests when the car is working or will I have to do this when its not working?

quote Originally posted by 86GT3.4DOHC: Also, make sure you have <10 ohms resistance between the distributor and the battery 0 would be optimal. A quick test when it wont start would be to clip a wire to the distributor and attatch that to the battery. If that fixes it, you have a grounding problem.

So i run a wire from the battery ground to the distributor base/ground correct?

Also todays update: didn't start at all in the morning when it was 50F, came home at 4 and it took two 15second cranks to start at 70F.

[This message has been edited by cloaked (edited 09-09-2008).]

You have to do it when it is not working, or they will test good. You can do these tests anytime the RPM reads 0 when cranking.

If they both test good, hook it back up and make sure RPM's still read 0 when cranking. If you get RPMs after testing, then the tests do not count since it might have started working when you were testing.

Pretty much though, if you ever get a bad test, that part is bad, there is no reason they should ever test bad. But, because your problem is intermittant, a good test does not mean the part is good, unless you can recreate the problem immediately after testing.

If you have a can of compressed air, like for a computer, you can try spraying the parts and see if they quit working. This wont work with an air compressor because the air doesnt cool that much when blown.

Yes, if its not working, connect a wire from the distributor to the battery ground, doesnt have to be a big wire, just any. If this makes it start working, you have a ground issue. Im not holding my breath for this one, but its always worth a shot. Again, if it starts working, disconnect it and see if it still works. If it stops working, theres your problem. If it keeps working, you might leave it connected for a few days and see if the problem disapears.

[This message has been edited by 86GT3.4DOHC (edited 09-09-2008).]

Ok.

btw I've got about 4 pink-ish colored wires. Can you identify the locations of the ones i need to jump instead of the colors?

[This message has been edited by cloaked (edited 09-09-2008).]

On top of the ignition coil there are 2 connectors, each has a white wire and a pink wire. The pink wire is 12v and the white is ICM\tach signal. Take the connectors off the ignition coil and connect the pink wire in the black connector to the pink in the grey connector.

[This message has been edited by 86GT3.4DOHC (edited 09-09-2008).]

My grey connector has two pink wires - lol. (this wire is off an old 85V6). But I just looked at a new connector on the fiero store, its the left wire on the grey connector.

Btw I dont know how I missed this before, but testing between the terminals on the pickup coil only gives me .5omhs... Can it even run w/ .5omhs??? lol

Since dist ground had 0omhs to battery, Its prolly 99% likely to be the one thing i haven't replaced - puc.

[This message has been edited by cloaked (edited 09-09-2008).]

No, that likely will not work. You should have ~820 ohms. Either you are testing wrong, or the PUC is shorted.

Put the meter on both terminals and crank, testing for AC voltage.

If you really have .5 OHMS and not K Ohms, then I would say its probably bad. Given the construction of the PUC, it would lend itself to thermal intermittant failure.

My old meter is apparently messed up, it reads ".4" in "1K ohm" mode and ".4" again in "10x ohm" mode. I got out a newer one and it reads ".825" in "K ohm" mode.

quote Originally posted by 86GT3.4DOHC: Put the meter on both terminals and crank, testing for AC voltage.

Did this and got ac voltage as described, but this was testing while it was warm and starting - not in the cold weather when it wont start. I'll do this test again tommorrow morning.

Do you remember what reading you got on AC? It would be helpful so I can tell people in the future.

But that does sound right on both tests, so let us know what happens when its cold.

quote Originally posted by 86GT3.4DOHC:Do you remember what reading you got on AC? It would be helpful so I can tell people in the future.

It fluctuated between .25 - .75 A/C V (this was on my old needle meter).

Btw, I'm getting 12v from both of the wires in the 2 wire grey connector going from the coil to the ignition modual - and its been this way for atleast a month that I know of.

Also, a month ago my ignition coil went bad, so I replaced it. Car ran fine for another three weeks, till that puc clip came off over a bump. Not but 12 hours after I replace that clip (so nothing new except pickup coil clip) I start having these issues.

[This message has been edited by cloaked (edited 09-09-2008).]

Oh yea, that kind of makes sense, the ICM grounds the (supposed to be) white wire to fire the coil, so there would be positive on the coil end of it.

Check the wire leading to the coil, one wire will go to the tach filter, the other has 12v on it with key on.

The coil connectors are like this B - Black Connector W - White wire P - Pink wire

So the two poles closest to the edge of the connector tie together, I believe they are the pink 12v lines.

II------------------------\
II \
II BBBBBBBBB \
II B B |
II B W P B |
II B B |
II BBBBBBBBB |
II |
II GGGGGGGG |
II G G |
II G W P G |
II G G |
II GGGGGGGG |
II /
II-----------------------/

quote Originally posted by 86GT3.4DOHC: Oh yea, that kind of makes sense, the ICM grounds the (supposed to be) white wire to fire the coil, so there would be positive on the coil end of it. II

I tested the icm side of the connector btw, but u probably understood that.

Also, this thread https://www.fiero.nl/forum/Forum2/HTML/081541.html says that double 12v on that connector means a bad icm. But again this tests the same wether car runs or not, and has tested this way for atleast a month now - and i wouldn't be suprised if it was like this for years.

-I dont really follow that diagram u drew, but I know which two wires i need to jump to bypass the ignition coil when I test the icm in the morning.

[This message has been edited by cloaked (edited 09-09-2008).]

Thats wrong, I tried to straighten things up at the bottom of that thread.

12v on both wires just means the ICM is getting power and the coil windings are not broken. There are still a couple other things that could be the problem.

Im really thinking it is the PUC at this point, but there is nothing wrong with testing to be sure.

Ok 10pm got down to 50F - wouldn't start. Jumped connectors, ground was fine, omhs on pcu were 815. Had someone crank the engine while i watch for a/c volts across the pcu - my needle meter just moved up ever so slightly to about 0.1 V and just sat there till cranking stopped -> went back to 0. This is defanately not fluctuating between .25 - .75 V like it was earlier when it was warm outside and starting up.

Hurray! Thank you 86GT!

What really annoys me though, is that I woulda had the pcu replaced last week when that clip came off, but the universal unit Murray's gave me was too tall and basically covered up the grove on the distributor that u need to put the clip in. So I just grabbed a clip out of the new pcu box, put the old pcu back in, and returned the new pcu... Shoulda just asked them to find me another brand that would fit...

[This message has been edited by cloaked (edited 09-09-2008).]

I skimmed everything except the first post, so sorry if I'm repeating. I noticed one person said grounds and you asked what grounds. Check the small ground wire coming from the battery to the chassis, and make sure the ground strap between the engine and the chassis is still there and good.

Overview of grounds is a nice triangle.

Battery to Engine BIG WIRE FOR STARTER

Engine to Chassis HELPS PREVENT GROUND LOOPING AND HELPS ENSURE GOOD GROUND WHEN RUNNING

Chassis to Battery This one I see gets overlooked a million times. if the other two grounds are in excellent shape then this one isn't as critical but is still needed.

So if any of these is questionable REPLACE THEM. Lack of a good battery to chassis ground and a missing or corroded engine to chassis ground will show low volts on the gauge even when the starter spins just fine. If the Voltage is too low to the chassis then you won't get the needed power to your ECM or Ignition.

Stu

quote Originally posted by cloaked: Ok 10pm got down to 50F - wouldn't start. Jumped connectors, ground was fine, omhs on pcu were 815. Had someone crank the engine while i watch for a/c volts across the pcu - my needle meter just moved up ever so slightly to about 0.1 V and just sat there till cranking stopped -> went back to 0. This is defanately not fluctuating between .25 - .75 V like it was earlier when it was warm outside and starting up.

*Scooby Doo Voice* Ruh-oh....

I would go ahead and replace the PUC because its cheap and easy, but im starting to wonder why you would have good resistance reading, but it not working. Unless it is shorting only when cranking.... At anyrate, your problem is definitely in there, but there is a chance it could be the magnet on the distributor shaft. Also, check and make sure the fingers on the distributor are all but touching the rotor thingy. You'll see what im talking about in there.

So go ahead and replace the PUC, we'll hope that takes care of it. Check the rest of the parts carefully while you are in there.

I've heard of others having a good resistance value, but still a bad puc. So I wouldn't be the first. That voltage reading is much more important - and I really doubt that it was the magnet getting intermitent.

Its cold out right now, and its been starting fine with the new puc in. Gonna consider this case closed 'Scooby Doo'. =)

Thanks for the grounding info DIY, I need to check and clean my grounds soon.