1992 Pontiac Bonneville • 6 cylinder FWD Automatic • 213,771 miles

Sorry should have said engine speed is normal, but at say 30 mph the tach is reading about 6000 rpm. ICM replaced and also the crank position sensor. I'll be replacing the cam PS tonight. Is there something else that controls the tack?
August 24, 2011.

Stock tach run of the ICM or sometime the negative coil lead.

The Tach signal wire is generally one of three wires from the ICM.
Are you running a stock Tach and stock ignition?

Does your car have a distributor or coil packs?

Let me know and I will watch for your reply.

The tach is stock replaced ICM tach still not working still reading high. It has the coil packs. Has 10 wires coming from ICM they seem fine. Only thing left to replace is coil packs and engine control computer.

Aug 24, 2011.
Try re-setting the ECU by disconnecting the battery, (or Main ECU fuse) for a minute. COuldn't hurt.
The reason I asked about aftermarket is because it is acting like it is reading a Multi-Spark or High Energy ignition. They throw off stock tachs to read high from the extra pulse signals the tach reads.

If you got a Multi-Meter with a dwell tach function it could probably eliminate the coils and ECU. Kindda leaving you with the tach.

Does the car run well?
When did the tach start to mal-function?
Let me know and I will do some research and watch fro your reply.