93 LT1 6-sp Engine dies, runs, dies

[Jack W.]

Changed the oil in the car Sunday; filled the car up with gas (Shell 93) on Tuesday and was driving along an Interstate Wed. Oh - car has 60,000 miles. After about an hour of driving, with all gauges "right on the money", the engine died - got a "check gauges" light and "Service Engine Soon". At the time, there was no response from the gas pedal; it just died. Pulled over, checked under the hood for anything obvious; cursed for about 5-10 minutes, got back in the car; it fired right up and no messages displayed. Drove it for another 30 minutes to a friend's house and everything was OK. Checked for DTC's - only one to show was Code 28. Left the car there, and returned on Friday. Drove towards home on a highway with some stop lights for about 40 minutes; again everything OK. Taking off from a stop light, the engine died again and this time, would turnover, but not start. After trying to start it a few times, once, for a few seconds it seemed to want to fire up, but did not, and the Service Engine Soon light remained on. For whatever reason, I did not check the codes at this time (I guess I assumed it would be 28 again).

The possibilities seem endless - some of them(?):

1) bad gas or water in gas - when I filled up on Tues, used a gas station I have never used before, but the car was running over a couple of days after that for a total of about 2 hours, so it seems that this would be low on the suspect list.

2) problems with fuel filter.

3) problems with fuel pump.

4) Code 28 - the service manual indicates Quad-driver module #3. In addition to the fan relay circuits, something is mentioned about an A/C request signal - at the time of both failures, the heating/AC system was OFF (and has not been on for weeks). Also, the documentation indicates that this code WILL NOT turn on the Service Engine Soon. Yet both times it died, the Service Engine Soon light came on. So this code is a puzzle.

5) ECM problem - ??.

6) Optispark - although with a problem here, wouldn't there be a complete failure rather than (what seemed to be) a gradual deterioration? The car has always fired up immediately after engaging the starter.

Any ideas or suggestions would be greatly appreciated, and
Thanks much in advance,

Jack Witmer

 

[vettenick]

Hi Jack!

First, let's attack the basics--when it cuts out, I would check what the fuel pressure is, and if you have spark output at the plugs.
Once we know what you have and don't have, we can isolate the diagnostics. Give me a yell if you need me.

 

[69MyWay]

My money is on a opti spark failure...and the code 28 is just there due to maybe the car cutting out during a duty cycle or something.

I have had my share of headaches with the opti unit. They will cause all sorts of strange problems.

Rough idle
miss fire
stall
cut out, then restart after they cool down
rich/lean running
etc. etc.

Your early model car is not vented. It can collect moisture over the years, and corrode the contacts and circuits.

Just do a search under opti spark on this forum, or any forum where gm cars use them (F body). You will see the same type of complaints.


However...since they are very expensive and will take you the better part of a Saturday to swap out...try all the direct and simple stuff first. Fuel pressure testing, spark testing, fuses, ground contacts, vacuum leaks, etc.

 

[sothpaw]

I agree with '69, having just had a bad brand new Opti, w/1500 miles only on it. And strangest of all, this one would run always as long as it was cold. Hit 190 deg. and it would die.

Also, car died again w/ some spark module being the supposed culprit.

I think what you have is an ignition issue.

 

[jmccloud]

Sudden death

I've had two 'in tank' fuel pumps (neither a Corvette) go with symptoms just like yours. Do you have gas at the rails? Pressure?
John - Elkton

 

[compyelc4]

Agree with 69myway.

Gut feel is the opti-spark. Check the codes again. Next time if she dies on start-up while in the garage, and won't fire, place a timing light on one of the spark plugs. My guess is you will get no fire. If you are lucky the opti will die altogether, making diagnostic on that puppy a breeze!

Ted

 

[Jack W.]

On the subject matter, for those of you who thought Opti-Spark - correct...........only I wish you hadn't been correct !

The dreaded Opti-Crap strikes again, which means new water pump, and while I'm there - plugs, wires, etc.

Thanks to all who responded - they were all good.

Jack Witmer