i bought the ebay tach repair board.i installed it this weekend.i used a scanner to see how much the tach was off.i tried to adjust the tach using the pot on the board.the problem was if i adjusted the tach to be right at idle it was off at 3200.i adjusted it to be right at idle.its only off maybe 150 rpm at three thousand.

Some one on here rebuilds the tach board, Hopefully someone will post who it is

Forum member JGunsett is the go to guy for Fiero instrument repairs.

quote Originally posted by richard in nc: i bought the ebay tach repair board.i installed it this weekend.i used a scanner to see how much the tach was off.i tried to adjust the tach using the pot on the board.the problem was if i adjusted the tach to be right at idle it was off at 3200.i adjusted it to be right at idle.its only off maybe 150 rpm at three thousand.

I'm not familiar with the Ebay repair boards, but I fixed mine myself about ten years ago, most likely using the same techniques and variable resistor. I too adjusted it so it is accurate at idle but it slowly gets more and more off the faster I go. That's fine with me; at least I know my idle is correct but I don't care as much if I am off slightly at 60 or 70 MPH. And now that I'm used to it, it seems perfectly normal.

I did that this weekend too, what scanner did you use?

quote Originally posted by bergertime: I did that this weekend too, what scanner did you use?

actron CP9145 I bought the repair kit from the cajun tach shop.

Note for All scanner users...

any value on the display is Delayed a bit. ECM isn't made to handle "2 threads" so only put out data to scanner ~ 1 or 2 x per sec & often idle RPM = 1000 regardless of Idle RPM in normal driving etc.

Match RPM @ idle is easy because you let sit ~ 1000RPM
but at higher RPM... can be very hard to push gas pedal @ whatever speed then get ECM to push out data.

Even 2 speed emission test is often hard to get ~ 2500 RPM on that display & that's not connected to ECM.

Is "safer" to use any standalone tach for this job & some others. But Many digital units have same problem & display are slow to update.

------------------
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Does anybody know what the values for the resistor and cap are for the tach ? I’ve looked at lots of tach threads and found nothing.
I put a tach filter from Rodney on and my tach reads waaaaaay high…..very easy to go high enough to have the needle push on the oil gauge needle.

OE Tach, & I believe Speedo, Two Cap/Resistor sets are needed...

1 CR set total range of motion. 0 to X ° of scale.
2 CR sets Max RPM.

1 or both changes for engine & trim level for given car & follows formula(s) in data sheet I don't have right now.
GM & most use standard cap values & "Laser Trim" the resistor to get final CR to get both setups.

search tach board

I don't know Ebay board. If uses same/similar "chip..." Sounds likes gave you "trim pot" to tune max RPM or Max ° but not both. If you set Max RPM but Max ° is off, then will display "wrong" at some point. Sim problem other way around.