LS1 PCM differences in tach output (F-body vs 04 GTO)

[Kevin Doe]

I have a 93 RX-7 that I swapped a 2004 GTO engine/trans/PCM into. I have wired all the factory dash gauges up to the LS1 PCM, and everything works besides the tach. Others who have done this swap (using an F-body PCM), just simply wired the PCM tach output to the factory dash tach, and everything works. From some research in EFI Live (which I'm using to tune with) I have noticed a difference in the GTO tune file and the F-Body tune files. Aparently the tach output has the ability to have a "12V pullup". The F-bodies have this pullup on by default, the GTOs do not. In my tune I have turned on this pullup, but still no change. My only guess is that there are differences between the two PCMs, and GTO does not have the hardware necessary to do a "12V pullup". I'm assuming that by "12V pullup" they're refering to a DC offset of 12V. If the GTO PCM does not have the ability to do the 12V DC offset, do you recommend a way to build a circuit that can add a 12V DC offset to the tach signal?

[Kevin Doe]

Well I called Dakota Digital and spoke with one of their tech guys. He said if a 12V offset is required, here is how i coudl make the circuit:

He said to run a 12V ignition-on wire, to a 10k Ohm resistor, and then tap that into the tach signal.

[GMPX]

Kevin, what the Tech guy said is exactly what the PCM does, it switches in a pull up to the circuit.
What is the HDW number on your PCM?, as you suspected, there is some out there that are missing certain output driver chips.

Cheers,
Ross

[Kevin Doe]

This is a pic of my PCM.

http://i93.photobucket.com/albums/l55/Kevin_Doe/RX-7/PCMsticker.jpg

HDW number 12583659

[Kevin Doe]

Ross, did you get a chance to check my hardware number?

[burtoncr]

Ross, I have the same problem (LS2 swapped RX7) only with the 06 GTO PCM (E40). The E40 tune file doesnt even have the pullup option, but it does have Crank (default), PWM, and Serial tach output options (G1201). Would any of those work to produce the same signal as a Fbody?

Thanks,
Chris

[burtoncr]

Nevermind Ross, I used a 12V 10kohm pullup resistor and it worked.

- Chris