So i picked up a 96 Z28 and the tach in the cluster doesnt work. Key ON it raises to 0 RPM, crank it over, it fires up barely raises to 200 RPM then falls back to 0.

I checked from Pin 13, white wire in the red connector all the way to plug in the kick panel area, continuity good. checked from the PCM plug all the way to the cluster plug, continuity good. Got a different cluster, does the same exact thing.

So i borrowed a small aftermarket tach, hooked it up to the white wire, does nothing... I then hooked the aftermarket tach up to the white wire on the ICM and it works perfect. Even though i know the signal is filtered through the PCM i thought id be cute and do a last ditch effort by running the cluster tach off the ICM white wire, the engine wouldn't even start then lol.

So i cleaned the female pin in the PCM connectors and cleaned the pin on the PCM and it made no difference. Is it possible for the PCM to just stop providing a tach signal out? or is it possible that something else that reports into the PCM with a signal either from the opti or coil etc?

The car does run just fine though, no misses or anything goofy otherwise.

Any ideas?

 

Use a multi-meter with a frequency scale to measure the pulse output at the end of the harness where it connects to the cluster. That will tell you if the signal is reaching the cluster.

The 93 runs the tach of the coil, using a filter in the line between the coil and the tach.

 

OK I tried that tonight, it had 55hz at idle and would climb up near 100 hz with a quick free rev to like 1500... So does that mean the clusters are fubar for sure then?

The cluster i bought is out of a 95 v6 camaro (110mph speedo) and everything else works with it too like the original, just the tach does the same ****.

ideas?

 

If the output frequency from the PCM continues to rise proportional to RPM, and the signal is present at the cluster, it would seem to be a cluster problem.

 

Well... Finally got my new cluster, a proper 150mph from another 96 car. Still don't work!!!! FML!

While I'm not totally sure how to check the frequency correctly, my meter reads hz, but usually it's meant for checking ac hz on generators.

Anyone got any other ideas? No clue how the he'll it could drop a tach signal out of the PCM???