FULLSLP1

97 Lt1 /auto/ stock/ 70k miles/ just died during cruise no prev probs. NOT CAR IN SIG

car cranks but will not start no codes only rpm is reading 13,000rpm on scanner (problem). here is whats been replaced. coil/optispark 2x/ plugs/ wires/CKPS. fuel pump shows over 40 psi charged and during cranking. injector rail was pulled and injectors are spraying there is spark from the coil to the opti but random spark to the plugs (thats why its had 2 opti's). The car was originally scanned using an autozone special and showed no issues but after all this other crap was replaced and still no start i scanned again and it showed the high rpm problem.....i assume now that the car won't start because the pcm thinks the car is starting at 4k rpm when in fact it is 400 rpm becuase it is pig rich and then when its about to fire the ecm reads its final 13k rpm which is way above the rpm limiter hence the spark and fuel cutoff.. why wouldn't the ecm read off the crank posi sensor and the cam posi sensor as a backup.......ANY IDEAS?

BUBBA

Why did you change optis twice? Have you tried borrowing/buying a cheapie, PCM and see if it makes a difference? Sounds like a distributor problem to me, especially because you say that it cranks, it has fuel pressure, juice to the distributor, but "litttle or no juice to the plugs". There isn't much more to consider than fuel, spark and distribution and timing of the spark.

One reason I suspect the distributor is that you changed it twice, so apparently it didn't work the first time---so why should it work the second time if it was not installed correctly or the distributors were no good---which is a coincidence, unless you bought them at 3 AM or for $20.00. JMHO

NJLT1SS

It could be the ICM. One thing I cant stress enough, if you are going to buy a new ICM, or any other sensor, get one from GM.



Nick

IPrice

I've had some sporadic conditions as well and am thinking that the ICM is bad. I plan on doing some diagnostic work when I get the time so that I don't end up just throwing cash at the problem. I'd love to find that my ICM is the culprit vice the Opti.

What is the norm price for a GM ICM at the dealer??

Thanks,
Ivan

BUBBA

I hear that. I picked up a used PCM when I first had my engine tuned---sent the used one in for a tune and kept the new stocker in a box just in case.

IPrice

Holy Crap!! Just got off with local chevy house. List on the new ICM is $149
"but he can sell it to me for $128."

Highway robbery!!!!!!

I wonder how many autozone/checkers/pepboys ones I can buy for that???

I better add in the tow bill too.

-Ivan

applecorn37

I bought an ICM from O'Reilly over a year ago for around $80. It's not from GM but its never given me any problems. They show BWD for $92.99 now.

Injuneer

Get a price form Jason Cromer.... typically a little over 1/2 of GM list, plus shipping. Shoebox has part # info, and pricing GUIDELINES..... I emphasize that it is a guideline, because I'm sure he does not have time to update the prices as fast as GM increases them.

1996-1997 Ignition control module
AC-Delco # 579
10482803
$61.41

It's going to be more than that price, but I doubt it will be $128. Generally, dealing with a local GM parts dealer is outrageously expensive.

http://shbox.com/1/4th_gen_tech2.html#Dal_and_Jason

FULLSLP1

Injuneer I had the ICM tested at a local shop and they said it was operational however I already dropped the cash on the opti. Do you think there still could be a problem with the ICM. Also I assumed the first opti DIDN'T work because I thought as all of you have that it must be the opti but just for giggles I swapped in a KNOWN WORKING OPTI so it was technically 3 opti swaps.. Whats up with the 13k rpms though???

Injuneer

The PCM determines RPM from the low resolution pulse pattern from the optical sensor in the Opti. If the sensor is faulty, or the signal from the high res part of the optical sensor is bleeding to the low res signal, or if you have excessive high voltage RFI interference with the pulse signals, you're going to get a strange RPM reading.

For a basic question, what are you using to scan the PCM? Since its not showing any codes, and producing a faulty RPM signal, it may not be compatible.

FULLSLP1

autoxray obd2 have used it on 40 plus cars . now i knew that the pcm retrieved its signal from the opti but why wouldn't it reference the signal with the crank or cam position sensor like most of the other major car manufacturers? What are the chances that this problem would have occured with three different opti's including the one off my other 97 ss. Is this where we should look for the no start?

Injuneer

The optical sensor is the cam position sensor in an LT1. Only the later ones like yours have a separate crank position sensor, and its only used for misfire detection.

High voltage RFI interference could be generated by a plug wire too close to, and running in parallel with the Opti harness. A damaged harness, or harness connector could cause the two signals (high and low) to contaminate each other.

I'm not challenging your skills with a scanner.... but I though the question was worth asking.

FULLSLP1

Thanks for the info , I'll swap out an opti harness and see what happens. all of the spark plug wires and the coil wire are factory located so any interferance would be harness related.