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Discussion Starter #1
:huh: Out on a cruise yesterday with the club and the engine started to miss and backfire and eventually stalled.

After a few miinutes it started and ran ok. However, if I gave any serious throttle it started to backfire and miss. At cruise speeds it was ok. The "Check Engine Light" did not stay on after starting. I made it home and now it is in the grage and wont start.

I checked fuel flow and it is about 42 psi. I checked for spark on one plug wire and its ok.

The ignition control circuit to the coil is getting 12 volts from the ECM.

I want to check OBD codes. (The 93 uses first generation OBD)Can I do that without a diagnostic tool? The manual says I can jump the diagnostic pin to ground pin on the interface connector and codes will display. But where do they display? Is it on the Driver info centre? Is there any need to check for codes if the "Check Engine" light did not stay on after starting?

ALso, if anyone has ideas about the most likely problem please comment. I'm thinking it may be the Crank position sensor? or the ECM? or the Opti-Spark distributor? Or maybe I skipped the timing chain. (It seems to be cranking at mormal speeds). Or maybe water in the fuel? But I dont know how to check these things out.

ANy help would be appreciated.
Thanks.
Mike
 

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Discussion Starter #3
-=Jeff=- said:
Sounds like the Optispark is going bye bye..

I would suggest replacing the Water pump at the same time too.
Thanks for the reply Jeff. Do I take it that you think the symptoms I described indicate the Opti-Spark?

I picked up a code reader and I have a code 41. The Haynes Manual indicates a timing/ignition problem caused by either the ECM or the Ignition COntrol Module. I got proper voltage readings from the ECM to the Ignition COntrol Module which indicate that the ECM is functioning correctly. So, out with the Ignition Control Module.

I have ordered a replacement and a new coil. I'll install them tomorrow nite and cross my fingers. If that doesn't do it, the Opti-Spark (and water pump) is next on the list...I guess.

I just hope its not the timing chain. I'm still not sure about that possibility.
 

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Discussion Starter #5
BubbleHead said:
Any updates yet?
I didn't get a chance to work on it yesterday. Work got in the way and then our Club meeting last nite.

I plan to pick up the parts this morning and get them on asap. I'll update you through this thread later today.

Mike
 

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Discussion Starter #6
BubbleHead said:
Any updates yet?
Up and Running! It was the Ignition Control Module. Its the little module with the single plug above the coil. It actually mounts on the same bracket as the coil with 2 very small bolts. Cost $150 Cdn.

At that price I suggest that anyone with a ('93) C4 buy one a keep it in the glove box along with the Haynes Manual and a GM Code Reader. Once the Code Reader showed a Code 41 (Ignition/Timing) the Haynes manual walked me through the diagnostics process to check the ECM to the coil and led me right to the Ignition Control Module. Once the diagnostics are out of the way it takes only about 20 minutes to re and re and it could be done on the side of the road with a few ignition sized wrenches.

Anyway, it was not the Opti-Spark, not the ECM, not the coil, not the fuel system, not the timing chain.

Obviously I am very happy to be on the road again at minimal cost.

Thanks for the interest and advice from everyone.

Mike :cheers:
 

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Mike said:
Up and Running! It was the Ignition Control Module. Its the little module with the single plug above the coil. It actually mounts on the same bracket as the coil with 2 very small bolts. Cost $150 Cdn.

At that price I suggest that anyone with a ('93) C4 buy one a keep it in the glove box along with the Haynes Manual and a GM Code Reader. Once the Code Reader showed a Code 41 (Ignition/Timing) the Haynes manual walked me through the diagnostics process to check the ECM to the coil and led me right to the Ignition Control Module. Once the diagnostics are out of the way it takes only about 20 minutes to re and re and it could be done on the side of the road with a few ignition sized wrenches.

Anyway, it was not the Opti-Spark, not the ECM, not the coil, not the fuel system, not the timing chain.

Obviously I am very happy to be on the road again at minimal cost.

Thanks for the interest and advice from everyone.

Mike :cheers:
Thats why you can't assume that a component has failed unless you run the corresponding tests to determine the failure.. well actually you can assume if you want to spend money throwing parts at a problem in which case unless your lucky you may be spending money that may not need be spent. OR you can assume if you just want to make an A$$ out of U and me LoL..

Anyhow good job mike on the diagnosis.. Glad to hear your back up and running..
-RIck:stick:
 

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Discussion Starter #8
VetteTech81 said:
Thats why you can't assume that a component has failed unless you run the corresponding tests to determine the failure.. well actually you can assume if you want to spend money throwing parts at a problem in which case unless your lucky you may be spending money that may not need be spent. OR you can assume if you just want to make an A$$ out of U and me LoL..

Anyhow good job mike on the diagnosis.. Glad to hear your back up and running..
-RIck:stick:
Thanks Rick. It's very satisfying to solve a problem like that without spending unecessary $$ for unecessary parts and actually get it right the first time!:excited:
 
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