J. L. Sonnier

I have a 94 w/ approx 80m miles. Opti (GM), plugs, wires, fuel filter, fuel pump & sock changed @ about 73M. The car is a basic 5.7 LT1 & to the best of my knowledge kas no mods except a K & N air filter and flowmaster exhaust.

The car killed on me (like turning off the key; no missing, surging, etc) & restarted very easily 3 times in less than 1/2 mile. I had it towed home rather than risking getting into traffic with it.

A mechanic friend came over & of course, it ran perfectly. He scanned it & got the following codes.
16 low resolution pulse failure
42 EST grounded
36 high resolution pulse failure
34 MAP sensor

Till I can figure out what the problem is, I dont want to risk getting in traffic & another wrecker bill.

The codes have been erased & the mechanic is going to check with a friend of his at the local chevy dealership to get some input.

Suggestions, recommendations etc would be appreciated.

mk842766

not familiar with the LT1(other than wishing I had one), but it sounds like it might be an ECM failure to me, with that array of codes... I would suspect the opti, with the exception of the last code...

Cheers,
Michael

STL94LT1

Looks like a bad opti.

J. L. Sonnier

It has been throwing the 34 Map code, but with no evident running problems; so the 34 code could have already been there when it started killing; does that ad any light? Also, how to test the ECM.

J. L. Sonnier

GM opti w/ less than 8m miles, garage kept, driven in rain once since replacing; do these things crap out that frequently? How do you test whether it is the opti? When it went out the first time, it would hesitate backfire & miss for a bit under strong acceleration.

STL94LT1

My first opti went at 12k, the second at 8k later, and the car was maybe driven in the rain twice in that timeframe. My car sat alot, and the Gen I optis seem to collect moisture when not in use. I've since upgraded to the Gen II vented opti.

RACER 1993

If you can start the car and just let it idle you will probably get at least the Opti codes again after a few minutes. If that Opti is going bad it will show up again soon without driving. The car can't run without the Low res. pulses. They are what tells the ignition to fire the plugs, and provide cylinder identification.

J. L. Sonnier

Racer: No problems starting. I took her out & drove about 5 miles; got on it hard a few times on the way; turned her off & let her sit for about 45 minutes; she started up fine; ran her the 5 miles home & got on her hard several more times. The 5 miles involved light traffic & several traffic lights. Absolutely no symptoms, & I did not notice the check engine light come on.
What else can I do to check out the opti &/or ECM.

pcolt94

I have 3 basic suggestions. The opti is the obvious of all choices and is characteristic of what happens as a multitude of symptoms can occur. My second suspect could be the ICM which might cause some runability problems but would not explain all the codes. Also check the coil wire for any arking just above the opti where it passes thru the water pump in close quarters.

I would clear the codes, run the car and see if they return or what result might be. It might be just unfortunate you received a bad opti. If it was early than a 94, I would look to the ECM. But the 94 and up uses an PCM which does basically the same, but is a much more reliable computer with less problems.