Cliffs: Car won't start but runs backwards a bit when I stop cranking. This started after I forgot to turn off ASR and romped on it. Sensors & codes look fine, and it is getting fuel.
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Full Description:

Symptoms:
My Z will not start, but after I stop cranking, it misfires extremely roughly and slowly for a few seconds, spinning the engine backwards several revolutions. This is followed by gray smoke slowly escaping from the air intake.

I remember that the backwards-running symptom has been noted a couple of times before, but in searching I found no posts confirming any causes or fixes. I suspect ignition timing would have to be off for this to occur.

The car started acting up on a road trip yesterday, with occasional stumbles (intake backfires, I think) during acceleration, and stalled twice but restarted. Seemed flooded for the restarts, as I had to crank WOT a bit each time. Finally, it conked out an hour from home and would not restart. After the flatbed ride home, it started OK once and ran great in both open and closed loop for several minutes of idling and revving in neutral, then stalled. Started a couple more times for shorter and shorter durations until finally it and wouldn't restart at all. No better today with everything cold again.

What I've tried so far:
Fresh recharge of battery, starting fluid, and repeated primes with the fuel pump have not helped. Neither did wiggling/re-seating the coil & ICM connections, which all look OK. Tried disconnecting MAF; no help. Cranked with throttle closed, 1/4, and WOT. Bled fuel rail, no air. Reset PCM.

Codes:
Had code 16 (Ignition low resolution pulse not detected) and code 33 (MAP sensor signal high) stored at first, but neither has reappeared since clearing them right after I got home. It did run again for a few minutes after that without setting any codes.

I do have a datamaster log of it running and then stalling yesterday.

Vehicle Condition: (12.2:1 LE 383 per signature)
-I can smell fuel at the exhaust, so at least it's squirting.
-Intake bellows and vacuum lines all pass visual inspection.
-MAP, Coolant temp, Air temp, TPS sensor readings are all normal and stable per Datamaster monitoring.
-Optima Red-top cranks many times on a charge, so battery capacity seems fine. Voltage around low 10s cranking, which is normal for my car. Cranking speed seems normal, too.
-Fuel sprays from Schroeder valve indicating pressure, but I have not verified how much with a gauge yet.
-Opti has about 5k miles, and looked great last year when I disassembled it to Locktite the rotor screws. I don't drive in the rain, but I did flush the heater core a few weeks ago, and could have dribbled on it. But I've driven it for several day's since then.
-Coil, ICM, & plug wires are also only a couple thousand miles old. Plugs maybe 1000.

This might be a clue: I forgot to turn the traction control off once yesterday shortly before all this started. When I gassed it, the tires spun a bit as the ASR did it's thing, altering timing and hitting the brakes while pushing up on the throttle. This may have caused the first backfire of the day, I'm not positive, but the car did buck pretty good. It seems like quite a coincidence that this was on the same trip, shortly before the trouble began.

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I'll run the 'no start' diagnosis in the service manual when I have time, but I'd love to know if somebody has already figured out what kind of malfunction can cause the engine to spin backwards like this!


Any suggestions on what to look at first???

 

Yep .... but with only 5k on it .... you WON'T like what I'm about to say .... it's the Optispark.

Mine behaved very similar to this just before the Opti "gave up the ghost". The major "clue" here is diagnostic service code 16 (low resolution pulse not detected) which was stored in memory, but is not now active. Like General MacAurther said ... it will return! (And it will probably bring along its "buddy" ... high resolution pulse not detected ... soon!). Also, you are correct, the "running backward" problem after/during cranking is due to the fact that the Opti is mistiming ignition signals to give you excessive spark advance. When spark arrives 60-70 degrees too early, it fires the fuel mix waaaay before the piston is anywhere near TDC .... and hence it "runs backward". Again, sorry to say this with only 5K miles on it, but .... that little coolant bath you "may" have given your Opti while flushing the heater core .... more than likely ......did it in. Good luck with this Jeff!

 

" .... you WON'T like what I'm about to say .... it's the Optispark. "

Truer words were never spoken - I prefer being in denial. With no code 16 now, I was hoping for alternatives. But, I suppose I have to accept that is the leading candidate. Thanks, Ken, you always have good input.

You're sure there isn't a secret reset button hidden someplace that I can just push to make it all go away?

I'll at least need to check the opti wiring better. That would be a plausible alternative.

 

Best I can offer you is this ..... disconnect that Optima Red Top battery from your car and let your PCM "snooze" for about 20-30 minutes. Re-connect your battery while you have your inductive pickup timing light hooked up on #1 and have someone else crank the engine. Look for ignition timing to be around 60-70 degrees before TDC if you get the "running backward" condition with NO start.

If it does start up ... check your then current ignition timing at idle, record it, and then dis-connect the timing light and take the car for a very short ride with ASR off ... and put a load on it. When you get a miss or hesitation or backfire under load .... limp the car back home and immediately run your codes. If you see either code 16 (low resolution pulse) or (I think???) Code 34 (high resolution pulse) ..... it's the Opti. Sorry

 

Yes, there is a button and it only works once. It's so hidden you won't even know you pushed it. It comes on every new, quality optispark.

 

Update to close out the question I posted with the solution. Yes, guys, it was the Opti. Great call. Thanks for the encouragement.

I ran all the service diagnostics first, and none indicated a failed opti. 2.5V AC on the ICM terminal, etc. Even the logged RPM and crank reference pulsewidth were smooth and solid during a stall event. I was very apprehensive that replacing that distributor would not fix the car, so I was actually very pleased when the failure was confirmed.

 

opti.

 

Just goes to show you how "diabolical" these Opti failures can be. With only 5K miles on it, and it passing all the service diagnostics, you just don't think it could/would be an Opti failure ...... but, nevertheless ........ it is!

 

OPTI I had the same problem 4 months ago, it drove me crazy because it was a new out of the box GM opti that was bad...