Fastbird93

Anyone have a schematic for this??? Reason I ask is because I have a 93 (the one that runs) with a 97 cluster in the car. Also had an MSD Digital 6+, and the tach worked fine. The Tach filter was still in the wiring harness. Recently, the MSD Died on me, so I trashed it and went back to the stock ignition. Knowing this, I removed the tach filter on the 93's harness to let the tach in the 97 get a signal.

However, it's not getting a clean signal at all. The tach is simply all over the place. It wouldn't move at all with the filter in the harness, so it's a step the right way, but what I need to find out is what kind of signal the tach is expecting to see so I can try to figure the right combination of resistors to wire into the signal like for the tach.

From what I remember, in the 93's the tach gets it's signal directly from the coil, through the in-line filter. Aparrently in 94, this was changed to the coil sending a signal to the PCM which then sent a signal to the dash tach, with no in-line filter.

I'm horrible with electrics, so don't laugh when I ask this: Would it simply be possible to measure the signal coming from the respective years locations (the coil output signal on the 93 and the PCM output signal on the 94+) and use resistors on my 93 to mimick the PCM output signal of the later cars?? If this is possible, would someone be willing to take a reading and get back to me??

Thanks for any help.

Shon Herron

subbing, b/c off my stock ignition I am not able to get any tach signal no matter where I try to get the signal....coil/PCM/etc.

Injuneer

The coil doesn't send a signal to the PCM. The PCM reads the RPM off the Opti low res pulse signal, then sends a signal to the tach from pin A13. The connection from pin B5 to the ICM tells the system when to fire.

The signal is not a matter of "resistance"... its counting pulses. You would have to know how may pulses the PCM sends to the tach.

Fastbird93

Hmmm......that poses a problem then since I don't know how I'd replicate that signal on the 93. Maybe I just need to ante up and get another aftermarket ignition box.

Shon Herron

That was my thinking but didnt want to run the risk of blowing up the opti, per some folks on here but never had that problem in my 94.....so who knows.