the tach shows about 400rpm more then datamaster. Is this common? What should I rely on?

Thanks

 

Yes, it is common for the tach's to display a higher reading. I trust the ECM value more then the tach.

RBob.

 

I've got a 1992 Z28 with a tach that's showing to be farther off than that. When I shift at 6500 rpm, as indicated by the tach, the computer is only showing 5,930 or so. I'm just going to install a shift light and set it 200 rpm below the rev limiter for now. I'll deal with the tach later (or remove it all and go aftermarket, this is a track car).

 

My '90's tach reads about 10% high.

 

thank you

 

I installed an autometer shift light tonight and with the 3,000 rpm test chip, I had to reach 3,500 on the tach to get it to light up. I'm going to assume (maybe incorrectly) that autometer isn't going to screw up a shift light and risk someone blowing an engine, so I am thinking the tach in my car is truly that far off.

 

My AutoGauge tach and my digicon have NEVER agreed on what the engine RPM is, the digicon is actually about 500rpm higher than the tach; when I first hooked it all up and set the shift light it would hit the rev limiter before the shift light would come on.

 

hmm strange. How hard can it be to build a working tach on a production car?

well. Thanks for the heads-up m8s.