Hey there, been having issues with my boys 97 Chevy C1500 (It's a vortec 305)- tons of em. We have been slowly resolving them one by one through the years. (bad trans shift solenoid, fuel pump, spider injector replacement, pitman arm seal, power steering pump replacement, ignition switch replacement).

We are currently chasing an electric ghost. Can't find a spec of reliant info online and don't wanna just go throwing parts at it......yet.

The issue is the tach display. When it's running it always shows a ridiculously high rpm. Idle at 5000, and a touch of the throttle tops it out instantly. It seems a bit low on bottom end power and it has always ran rich, I wonder if it's related? No bogging out from a dead dig, fires right up, just feels a little sluggish. Could this rpm reading be getting fed back to the computer and causing funny fueling?

We have a multi meter, not pros with wiring diagrams, but can usually fumble through them with some help.

I'd love to get his truck rocking like it used to! I hope to find some starting points from the pros here. Thanks in advance!

 

The tach signal is directly fed from the white wire on the ignition coil (if it’s still stock - if the wiring has been repaired/replaced, it’s terminal B). It’s probably not related to running rich - the PCM gets RPM readings from the crank sensor.

I’m not sure exactly what would cause it to read high like that other than some kind of signal interference or a bad tach. Verify the wiring is in tact and not shorted to ground/voltage between the ignition coil and terminal 6 of the cluster connector (cluster will need to be removed).

Have you been able to verify the actual RPM? Some digital test lights will read out RPM, otherwise you can use the frequency setting of a meter to check it. Some of these trucks had a tach lead spliced into the harness near the coil for that very reason.