At 70 mph my tach reads 3000, tunerpro rt is showing 22xx.
The car is a 89 RS which came with TBI but has been converted to the 165 ecm from a TPI car a well as the wiring harness from the ecm to under the hood. I do have a MSD 6a box.
Is there any way to adjust the tach?

I'm running 265/50-15 tires, 3.73 gears with .63 final drive in the T5.

 

The tach hooks up to the low side of the coil, and just counts sparks. The ECM and ignition and all that doesn't matter. Except, if you hook it up to a MSD without using their wiring adapter, it will read ridiculously off; like 5 times what it should.

The factory tach is not an "instrument" in these cars (or any other stock cars, for that matter); it's a trim package. As long as it has a pointer that waves back & forth and pleases the driver, then it meets factory specs. Don't waste too much mental effort on it.

These particular ones almost always fail by reading way high. If yours seems like it's reading high, it probably is. Just about all of them read high to some extent.

Check it against a piece of test equipment, in other words, an actual instrument. Something like a professional engine analyzer at a tune-up shop or a dealer service dept.

 

I didn't use msd wiring adapter I but I did wire it in the way their wiring diagram showed.
The rest of the gauges are off to, but they read low, the volts read below 12 but when I put a tester on the battery it will show 13+ as well as tunerpro will show 13+. I think I will do away with the factory gauges and install something that reads correctly.
Thanks for the info.