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91 Z28 no spark

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Old 03-15-2018, 11:21 AM
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91 Z28 no spark

alright, so I’ve been battling this no spark issue for quite awhile now. It all started when I went to pull into the gas station and the car just cut off. Went to go start the car again and it just cranked and cranked, every other crank it would back fire just a small amount. Long story short I got it towed home and it sat for a while before I started to mess with it. I’ve changed the cap and rotor, new ignition control module and new coil. I decided to test the pick up coil today and it only fluctuated between 0 and .5 volts. I read online that it should fluctuate between .3 and 1.8 volts. Everything else has tested out okay. I’m stumped, even with that low of a reading on the pick up coil would it still be a good part or is my pick up coil the problem? Tired of throwing parts at the car and not getting anywhere. Thanks in advance guys.
Old 03-15-2018, 11:34 AM
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Car: 1967 Camaro, 91 z28
Engine: Lb9
Transmission: M20
Axle/Gears: J65 pbr on stock posi 10bolt
Re: 91 Z28 no spark

Do you have power to the coil and icm (pink wire).
Old 03-15-2018, 12:09 PM
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Re: 91 Z28 no spark

Okay, I just tested both sets of pink wires. The top set of wires with the key on read 23. The bottom set read nothing while cranking and with key on.
I probed the end that would connect to the ICM and got nothing. The top set I tested with it being unplugged from the coil.
Old 03-15-2018, 12:11 PM
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Re: 91 Z28 no spark

There you go !
Old 03-15-2018, 12:16 PM
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Re: 91 Z28 no spark

So is it the coil or the wiring to the ICM? I’ve already tried two different coils and got nothing from it.
Old 03-15-2018, 01:46 PM
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Re: 91 Z28 no spark

I think Koeo and cranking you should have 12v on bolts pink wires you can take off the one to the coil to icm and ohm the wire.
Look at image 1

Old 03-15-2018, 02:47 PM
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Re: 91 Z28 no spark

If you do have to repair the jumper you can find parts on eBay.
https://m.ebay.com/sch/i.html?_from=...=tbi+coil+wire
Old 03-15-2018, 07:25 PM
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Re: 91 Z28 no spark

I tested diagram one key on and cranking and got no reading at all. I’ll double check it again tomorrow and if no luck I guess I’ll replace the connector and see if that does the trick.
Old 03-15-2018, 07:41 PM
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Re: 91 Z28 no spark

Pull off the jumper and ohm the pink and white wire. Sounds like the icm isn’t getting power from the coil.
Old 03-17-2018, 10:29 AM
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Re: 91 Z28 no spark

Been busy with work so I haven’t got the chance to look into it. When I do, (hopefully I’ll get time today) I’ll post my results. Appreciate all of your help.
Old 04-01-2018, 12:00 PM
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Re: 91 Z28 no spark

Okay, I know it’s been a while but I finally found some time to mess with it again. I hooked everything back up and got it the way it should be. I just tested diagram one KOEO and I’ve got 11.3 volts coming from the coil to the ICM now. Battery is pretty drained from sitting so I’m gonna charge it up and see if I can get anything out of it.. I’ll update ya soon.
Update: Still no start!
decided to check the resistance on the pick up coil while I was at it and that tested out at about 732 from what I read that’s a good reading. I’m lost.

Last edited by VictorGBKirk; 04-01-2018 at 02:59 PM.
Old 04-01-2018, 03:30 PM
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Re: 91 Z28 no spark

Even though the pu coil checks out I’m wondering if it’s bad.
I can’t think of any other solution.
Old 04-01-2018, 03:59 PM
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Re: 91 Z28 no spark

so I just pulled a plug and grounded it out and whatya know, I’ve got a weak orange spark. So at least we’re getting somewhere. The wires on the pickup coil look like they’ve definitely seen better days. I moved them around quite a bit when I checked the resistance on them. Could a bad pickup coil lead to weak spark or no?
Old 04-01-2018, 04:44 PM
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Re: 91 Z28 no spark

I’m not sure on the pu coil and weak spark. I would think it’s ok now that you have spark. Not sure what to tell you to try next . Is you battery ground clean on both ends.
Old 04-01-2018, 05:41 PM
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Re: 91 Z28 no spark

Yep, I pulled all of the plugs and they were pretty fouled with carbon deposits so I’m gonna pick up some new ones tomorrow and see if that helps the cause any. I appreciate all of your help though.
Old 04-13-2018, 12:00 PM
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Car: 91 Z28
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Re: 91 Z28 no spark

So, today I went back thru and hooked everything up, hooked the battery up to my Jeep to jump it and it’s getting fuel and spark now but when it turns over after igniting a spark it just stops turning over all together, and if I keep holding the key it’ll crank again, fire 2 or 3 times and then stop and repeat the process... it’s being jumped while doing this also. It’s got a new starter on it btw too. Any ideas? Could it possibly be that the timing is off? Timing chain maybe?
Old 04-13-2018, 12:05 PM
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Re: 91 Z28 no spark

The timing might be overly advanced. Try retarding it some .
Old 04-13-2018, 12:23 PM
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Re: 91 Z28 no spark

Will do, going to pick up a distributor wrench when I head back to town today.
Old 04-13-2018, 12:25 PM
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Re: 91 Z28 no spark

Just curious was the distributor out when the icm was replaced ?
Old 04-13-2018, 01:39 PM
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Re: 91 Z28 no spark

Nope, distributor hasn’t been removed since I’ve owned the car which has been about 4 years now. Kinda getting ready to send it off to my buddy’s shop bc I’m tired of messing with it.
Old 04-13-2018, 01:51 PM
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Re: 91 Z28 no spark

Originally Posted by VictorGBKirk
Nope, distributor hasn’t been removed since I’ve owned the car which has been about 4 years now. Kinda getting ready to send it off to my buddy’s shop bc I’m tired of messing with it.
That kinda rules out timing unless the chain has slipped which I would think might cause low compression and easy cranking.
Compression test and double check battery ground and positive connections. I hope you get it figured out without to much aggravation.
Old 04-13-2018, 03:23 PM
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Re: 91 Z28 no spark

Have you verified the ignition wire from coil to distributor is good?
Old 04-13-2018, 04:24 PM
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Re: 91 Z28 no spark

Originally Posted by ULTM8Z
Have you verified the ignition wire from coil to distributor is good?
yep, test out at 11.3 volts with key on.
Old 04-13-2018, 04:26 PM
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Re: 91 Z28 no spark

Originally Posted by Tuned Performance
That kinda rules out timing unless the chain has slipped which I would think might cause low compression and easy cranking.
Compression test and double check battery ground and positive connections. I hope you get it figured out without to much aggravation.
yeah, I guess I’ll just give it a complete rundown. Might be overlooking something simple. Appreciate all of your help thru the process.
Old 04-13-2018, 05:18 PM
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Re: 91 Z28 no spark

Originally Posted by VictorGBKirk


yep, test out at 11.3 volts with key on.
That's the primary wire. I'm talking about the secondary high voltage wire going to the distributor.
Old 05-20-2018, 06:12 PM
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Re: 91 Z28 no spark

So I finally said whatever and adjusted the timing and it ran as smooth as it should. On my way back home with it, I put my foot into it and whaddya know. Started backfiring and couldn’t hold an idle. It runs fine on start up sometimes and then other times it’ll run like complete crap. Any ideas to this now?
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