Corvette C4 Forum 1984 through 1996

93 LT1... No run - No spark, No tach

Old 05-12-2014, 01:54 PM
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Join Date: May 2014
Posts: 4
Default 93 LT1... No run - No spark, No tach

Hello everone,

Got your thinkin' caps on? This will probably turn out to be something very simple... or not!
Background: 1993 Torch Red 6 speed coupe. Awesome ride! 162K miles.
The day I got it, it died on me on the 91 freeway, I was going about 70 in 4th gear (Forgot I had 2 more) It lost power, then just before I rolled to a stop it re-ignited. No other problems other than trying to use the power locks and activated security system so no crank. Locked and unlocked doors with key, waited 3 minutes: Vroom Vroom!
1 week later Water pump let go, Changed it out no problem. I did not change the opti at this time. Ran great.
1 month ago I was stuffing it into an entrance ramp to merge into traffic. A hard right, turn hit about 80 and pop!... died again. Same as last time just before I rolled to a stop it fired up again. New fuel pump and filter. Ran great. Except it would run rough and puny sometimes as I was accelerating. Never got any ECM codes except DTC 12. Did not know about CCM codes so did not read.
2 weeks ago: I was entering another ramp for East bound I-40, Laying the coal to it, another hard right hand turn, I was doing 110 and pop Nothing again. I had enough velocity to notice some things this time. The tach was on Zero even though it was turning over with the key on. Usually I get some rpms even when cranking. I also had the ASR light. This time It would not re start though.
Got it home and in the garage. So okay I thought it has to be the OPTI! So I ordered a new one from Petris Enterprises. It is absolutly gorgeous Red with black potting compound. It is a shame no one will see it after the water pump is back on. It is modified like the late ones with the positive venting. So I put it on and tried to fire the beast up. No spark! So I began the troubleshooting.

DTC 12 and DTC 16.(I didn't have the 16 until I put the new opti on)
CCM - C12 and H16. Module 9 I get ---.
FSM had me take a jumper and jump "B" on the gray connector to unhook the tach (can anyone explain why?) and probe the 2 center terminals of the ICM harness for voltage. I got .5 and 0 volts. This points to bad ignition circuit 3
Oh, fuel pump runs. I have 46 lbs at rail. Did not check injectors with 'noid light since I have a no spark condition to run down first.

I have read Dipstick's post about the Tach Filter. I have not gotten a DTC 62 (No tach Pulse) as he did though. I believe my car has been modded. The FX3 shocks have been replaced with Bilsteins and connectors are not hooked to anything and it sets no codes saying signals are missing. Should it?
So what would you guys do next?

1993 Torch Red Coupe
2011 Ram Big Horn (Of course it has a Hemi!)
2008 Solstice Vert (Wifes Driver)
1988 35th Anniversary Coupe (Wifes )
Old 05-13-2014, 09:20 AM
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Default Update

Well I went back and dug into the book again. I had the battery out checking connections around it and when I put it back in I pulled the codes:
ECM "C12"
Module 1 - "C12"
Module 4 - "---"
Module 9 - "---"

Cranked engine for 15 seconds, no new codes set. Went to Troubleshooting chart "C4" in FSM. Jumped "B" connection of gray connector to unhook tach
Observed 12 volts on pins "A" and "D" of ignition module harness. Pin "C" has continuity to ground. Had wife crank engine while checking for 1-4 volts on pin "B" No AC voltage present. Now book says to go to page 2 of 2 on Chart C4. And it calls for a "Tech 1 to check for presence of low res pulses. I have no code scanner. Looking like ECM is bad! ACK!
Old 05-14-2014, 08:19 AM
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Join Date: May 2014
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Default Fixed!

Like I said something simple. It turned out to be the ICM (Ignition Control Module) I don't know how I missed it in the troubleshooting flow chart. I will have to have another look at that chart .
Anyway later guys.
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