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Old 11-17-2012, 03:14 PM   #1
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Default 93 z28 ignition issue

Recently I have been having an issue with my ignition system. I am able to start the car and drive it for a short distance, but then the ignition system cuts out. Sometimes when I had coasted almost to a complete stop, the ignition system comes back online and I am able to drive on with what seems like no other issues.

I have replaced the plugs, plug wires, coil, ICM/ECM, optispark cap and rotor, but to no avail.

It first started when the cap I had first overheated and warped causing constant misfires.

I am pretty much lost at this point at what the issue could be. I beginning to think that sometime when the first cap overheated, that the optical drive and other internal components may have been damaged.

I recently checked for an arcing at on the plugs and plug wires and I have not found anything of the sort.

At this point, any advice or points to check would be greatly appreciated.

Last edited by anolan1024; 11-17-2012 at 03:18 PM.
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Old 11-18-2012, 10:21 AM   #2
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Have you checked the opti wire harnes and it's connectors. It runs between opti and passenger side of intake. Wiggle the harness while car is running to see if car quits. Also check connectors and pins.

Electrical part of ignition switch, located under the dash attached to steering column can cause these problems also.

Check coil and icm connectors and wires. Did you put heat sink compound on back of icm and it's heat sink when you replaced it? If you didn't, icm will burn up in short order.

Go to sticky threads of this section and open the diagnosing the opti thread. Watch the video and run the tests. www.shbox.com also has opti testing, as well as, coil testing proceedures.

www.bbbind.com has most all 93 wiring diagrams you can view or download. PM me with your e-mail address and I send you the pdf files of ecm pinouts and ecm wiring chart to help you.

Have you checked for codes as not all codes light the ses. DTC's 16, 41, & 42 are all ignition codes that will stop your car from running, when active, but don't light the ses. Your 93 is unique in the lt1 family because you can read the codes by shorting the dlc terminals together with a paperclip. Short terminal A to B.

Lastly, I would put your car on a obd1 scanner that does running sensor data scans. Amazon sells the Actron CP9145 obd1 & obd2 scanner for around $140, a good investment as it will read your car and newer obd2 cars also. However you will need the CP9127 GM 12 pin dlc adapter also for $35

Last edited by cocobolo95; 11-18-2012 at 10:31 AM.
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Old 11-20-2012, 08:41 PM   #3
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Thanks for the reply,

All of the wires from the coil, icm, plug wires are all connected and appear to be no issues.

ICM does have thermal grease on the back of it. I made sure the it coated the whole surface when it was put on about a month ago.

I ran the codes and for some reason the code 16 started showing up. I have a more narrow area to focus on now. I was planning on testing the opti wire harness tomorrow and then if necessary replace the optispark.
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Old 11-20-2012, 09:39 PM   #4
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if the cap got that hot, you can bet something in the optical section got screwed too

its odd, those symptoms are classic ICM failure
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Old 11-20-2012, 10:29 PM   #5
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DTC 16 is the opti kiss of death, though you might luck out and have it caused by the opti wire harness and not the opti itself. I'll be hoping for the wiring harness.
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Old 11-21-2012, 08:18 PM   #6
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So the opti did have quite a bit of oil and water inside and around the sensor.

One last question, is there anywhere I can find the spline shaft for the opti? The spline gear in the last one seems to be one piece with the bearing. The new one I have didn't come with the spline gear for whatever reason. I've search multiple places, but haven't had any luck finding one unless i just need to go to the dealership to find one.
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Old 11-21-2012, 09:18 PM   #7
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Msd optis have spline built in, but oem opti should have removable spline shaft. I've never looked at the import optis being sold to see if shaft comes out.

Shaft is not listed as a spare part by GM, if it were, it probably would be discontinued by now .

I suggest looking on craigslist for someone parting out a 93-94 f-body or 92 corvette. You can usually pick up a used type one opti pretty cheap, just make sure it has the removable spline and has it with the opti.

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Old 11-21-2012, 09:25 PM   #8
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This happened to my wife while I was deployed. It ended up being my opti. I chose to go with MSD pro billet and I have beem super impressed. If this is what you decide to do order from East Coast Performance as I did. I bought my $515 MSD for $436. Plus for $120 they will rebuild their opties which is cheap compared to new ones. Remember I am partial tho and my perfomance improved over other ones.
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