Tachometer drop out <<SOLVED>>

[lunchboxx]

So far this has happened twice. Both times after the car has run for a while, the car will shudder and the tach reading will go to 0. All other guages read normal and the car seems to run fine. I have just replaced plugs and wires ( it was just time for it) and while i was in there, i verified good ground on the ICM ( it was tight, non-corroded, and the wires looked good.). The coils are to spec on primary and secondary resistance. I also pulled the wiring harness off of the ICM and made sure it was connected nice and tight ( and added some dielectric grease for good measure). Is this a crankshaft position sensor starting to die? The service manual says that the car will run without a crank sensor signal ( it just uses a different reference signal to run) but the car will start right back up again. If the crank pos. sensor was all the way dead, it would not start at all. Also, the tach signal comes right back after restart.

Aren't intermittent problems just the best things ever? so much fun.

I appreciate any help that anyone has on the topic.

[nos4blood70]

From what I've seen before, it's time for a new crank position sensor, even though it hasn't failed in such a way that it crippled the car.

[lunchboxx]

Thats sort of what I figured as well. The TACH gets the signal from the ICM, which cleans up a signal from the Crank Position Sensor. So for the tach to drop out like that it means Crank Position sensor, ICM, PCM or stepper motor. The ICM is firing the coils or the car would not be running right, the PCM seems ok for all other systems in the car.

That leaves the stepper motor ( which seems unlikely because the stepper would just stop where it was and not drop to zero) and the crank position sensor.

I just try to not be a "swap-tronics" kind of guy. I try to actually use logic to find what the actual problem is and fix it once and done. Unfortunately, I do not own the proper electronics to actually test the crank position sensor or the ICM.

[1oldman]

On the 1992 SSE I have, when the ICM got hot, the car would die. When it cooled off, the car would run. The Tach didn't work properly for a couple of years before it started failing bad enough to keep the car from running. - BC

[lunchboxx]

I don't think it is the ICM. The car runs and idles good hot or cold. Just randomly will shudder and then tach drop out. I think that the shudder is the misfire from losing the crank signal, but the computer has no codes stored at all. It sure is a chin scratcher.

[lunchboxx]

Ok, wanted to update this post and ( hopefully ) close this topic out. Just got the car back from the dealer. They did the sensor replacement and C.A.S.E. learn procedure, and the car seems to be running great again. Also I thought that I would add some info. I was also having "SERVICE STABILITY SYSTEM" alerts in the DIC. I thought that these were unrelated issues, but the dealer says that they are related. The dealer scanned the car and found a P0333 code set ( but no MIL light was on) and no other codes. Since I picked up the car from the dealer, I have not seen an alert, so maybe they were right.

I will be glad to have this one behind me and put many more miles on my Bonnie.