Problem with tach on a 89 firebird ls1
Hello I have a problem with my tach on my 89 firebird with ls1 engine. I bought the car and the previous owner had installed an aftermarket tach and 5 inch tach with tach adapter model 9117. The original cluster is also connected to the tach adapt. In short, my problem is that when I presses on the accelerator, my original cluster drops to 0 and when I release the throttle it goes back to the rpm of the aftermarket tach. Is that the problem is someone has already happened. thank you
Hello I have a problem with my tach on my 89 firebird with ls1 engine. I bought the car and the previous owner had installed an aftermarket tach and 5 inch tach with tach adapter model 9117. The original cluster is also connected to the tach adapt. In short, my problem is that when I presses on the accelerator, my original cluster drops to 0 and when I release the throttle it goes back to the rpm of the aftermarket tach. Is that the problem is someone has already happened. thank you
five7kid
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May 4, 2026
Welcome aboard thirdgen.org.
I moved this to the engine swap subforum for LS swaps.
Sounds like you need the signal boost mod (or whatever it's called). Basically tap a switched 12v source, put a resistor in it to the tach output from the PCM to give it more voltage to drive the stock tach. https://www.thirdgen.org/forums/ltx-...ch-issues.html
I moved this to the engine swap subforum for LS swaps.
Sounds like you need the signal boost mod (or whatever it's called). Basically tap a switched 12v source, put a resistor in it to the tach output from the PCM to give it more voltage to drive the stock tach. https://www.thirdgen.org/forums/ltx-...ch-issues.html