Hammerhead1445

Finishing up a LS1 motor/ T56 tranny swap from 99 F Body to a 2004 Miata. Followed Flyin Miata's instructions for voltage step-up with 2.2 kohm resistor, but no tach response. Suspect their instructions are correct for a later model drive-by-wire crate motor and harness application like they use, but not quite right for my older F body PCM. Anyone already solved this problem? If not, anyone know what the waveform is that the Miata tach is looking for? Have also heard that there are different tach settings available in the LS1 PCM which could solve my problem (perhaps a "crank sensor" setting). I know there is a tach signal of some kind coming from the PCM because it will drive a shop test tach I had laying around. Any help much appreciated!

fmowry

iTrader: (14)

You should post this in the conversion section. Are you sure you have your tach out from the PCM to the correct input at the cluster? FM's directions worked for me. OK, I did my conversion before their instructions were up, but it's the same. 2.2k resistor. Been a while since I did my wiring, but I don't think you need to change the PCM output to get the correct tach reading.

I'm using an '04 GTO PCM which is pretty much the same as yours.

Hammerhead1445

Thanks for the reply. Connected the resistor and LS1 PCM wires per the FM instructions and verified wires colors in Mazda wiring manual for my 04 Miata. Beginning to think I may have a setting wrong in the PCM for the tach, but waiting to hear back from the guy that did the mail order tune. Funny thing was when I hooked up the aftermarket electronic tach I got a reading that did vary with engine speed, but it looked to be about half what the rpm should have been. Hmmm....

Hammerhead1445

Oh yea, took your advice and posted to the conversion section.