E38 Tach

[minytrker]

How can I run an autometer tach with a E38? What do I need to change the tach signal to in the pcm?

[minytrker]

need help asap!! have to have this finished by tonight

[GMPX]

The ECM Output needs a resistive pull up to 12V. Put one side of a 1K resistor on the Tach output pin the other side to 12V IGN. Unfortunately the ECM has no built in 12V pull-up like the old LS1 PCM did.
Might want to also check if the Autometer has the pull-up built in. I don't think they do though as this small mod has needed to be done on every Autometer Tach I've seen on the E38 / E67 installation.

Cheers,
Ross

[minytrker]

So the 12v side and the tach wire will be on the same connector?

What do I need to set the tach at in EFI?

[GMPX]

So the 12v side and the tach wire will be on the same connector?

No, you don't connect the tach wire to 12V.
On the tach pin (on the ECM), connect the tacho wire, then on the same pin put one end of 1K resistor, the other end of the resistor goes to the 12V IGN.

What do I need to set the tach at in EFI?

I have a feeling the tach signal is always there. I don't have EFILive on this computer to confirm the setting but if you just change it from Serial to Crank (or something like that) it should be fine.

Cheers,
Ross

[minytrker]

Im still lost, like this? Sorry the horrbile drawing just did it really quick in paint.

[GMPX]

Spot on Lorenz, that is how it needs to be.
I just looked at the file I had done for the E67 conversion I assisted with and the Tacho is set to Crank. Then change the pulse count on the High and Low to match the RPM in the scantool to that shown on the Autometer Tach.

[gmh308]

Spot on Lorenz, that is how it needs to be.
I just looked at the file I had done for the E67 conversion I assisted with and the Tacho is set to Crank. Then change the pulse count on the High and Low to match the RPM in the scantool to that shown on the Autometer Tach.

Was this one of those E67's from the GMPP kit Ross?

[GMPX]

Yes, but it was reflashed to a standard GM calibration as the GMPP refused to run the engine (not sure why). I think we just stuck a 2006 CTS-V tune in it.

Cheers,
Ross

[gmh308]

Yes, but it was reflashed to a standard GM calibration

as the GMPP refused to run the engine (not sure why).

I think we just stuck a 2006 CTS-V tune in it.

Cheers,
Ross

Well I guess that's a good start . One of the "hidden" extras required.