Heres the story...I have a 1994 LT1/4L60E in my 86 S10. I am trying to get
the factory tach to work. According to JTR(the gurus for V8 S10 swaps) I am supposed to replace a capacitor in the tach signal to calibrate for the V8.
Link to tach mod

Its not working, at idle it seems about accurate but when I rev it up the tach barely moves, so I am wondering if the signal coming out of the PCM is any different creating my problem???

When i put my volt meter on the tach signal, switched on reads 12vdc, at idle reads about 5vdc then when i rev it the signal drops to around 1vdc.

Any help....besides installing an aftermarket tach

 

The signal will vary in frequency not level. You can't measure that with a voltmeter and especially not set to DC. Looking at the link you provided, the cap thing is not precise and you will need to experiment with the proper value. You will need another tach to prove out the mods you do to the IP tach. Not an easy task.

The first thing to find out is where does the s10 usually get it's tach signal. If it's from the coil, you may have a compatibility problem. If the signal from the coil was varying from 0 to 12 volts and the new signal varies from 0 to 5 volts, you may never trigger the signal in first place.

Capeesh.

 

hey thanks for the reply. I got it working by tapping into the signal directly at
the coil....not sure why the pcm output wouldnt work.