E67 Tach signal pinout

[HBHRaing]

Hello all. We have an E67 ECM that is being used with an 08 TBSS motor swap into a Jeep. The last issue we have is the tach signal. We are using the stock jeep cluster and PCM for the gauge, and a conversion box supplied by the manufacture of the swap kit. Our problem is the tach wire. Its been set to the White wire on connector X1, Pin 25. When we looked at the ECM, we found that it was set to serial data, instead of the crank signal that we needed. We set it to Crank, but I think that like the E38, The Tach output will now be on a different pin. What I need is the correct pin location. I have been searching around and have found that on the E38, it is C1, Pin 48. However on the E67, that pin in already in use. Any help would be great. Thanks.

[Taz]

Hello all. We have an E67 ECM that is being used with an 08 TBSS motor swap into a Jeep. The last issue we have is the tach signal. We are using the stock jeep cluster and PCM for the gauge, and a conversion box supplied by the manufacture of the swap kit. Our problem is the tach wire. Its been set to the White wire on connector X1, Pin 25. When we looked at the ECM, we found that it was set to serial data, instead of the crank signal that we needed. We set it to Crank, but I think that like the E38, The Tach output will now be on a different pin. What I need is the correct pin location. I have been searching around and have found that on the E38, it is C1, Pin 48. However on the E67, that pin in already in use. Any help would be great. Thanks.

C1 (Blue) pin 25 is where the Tach output will be - with an E67 ECM running a Trailblazer tune. The stock Tach setting in a Trailblazer is PWM - if memory serves. Changing this setting to "Crank" does not change the output pin of the ECM. When set to PWM or Crank the Tach output will be via the previously described pin.

Check your wiring. If everything checks out, your Tach setup may require a pull-up circuit to amplify the Tach signal sent from the ECM.


Regards,
Taz

[HBHRaing]

C1 (Blue) pin 25 is where the Tach output will be - with an E67 ECM running a Trailblazer tune. The stock Tach setting in a Trailblazer is PWM - if memory serves. Changing this setting to "Crank" does not change the output pin of the ECM. When set to PWM or Crank the Tach output will be via the previously described pin.

Check your wiring. If everything checks out, your Tach setup may require a pull-up circuit to amplify the Tach signal sent from the ECM.


Regards,
Taz

We have switched the setting away from serial which is what was set up when it arrived. However we have no signal at all, just voltage (near 12V). I can wire a pull up circuit on the system to see if that gives me anything. I have seen several different OHM values called for, do you know what value would be good to try? Thanks for the reply.

[Taz]

What Tach (Jeep IPC / Auto Meter / etc.) are you trying to use ?


Regards,
Taz

[HBHRaing]

Stock Jeep PCM (97 Wrangler), Stock Cluster. Between the GM Tach signal and the Jeep PCM is an emulator from Novak that takes the 2 Pulse/rev Signal from the GM tach wire, and converts it to a Jeep Cam/Crank signal. That signal is then converted in the Jeep PCM and sent to the cluster.

[Taz]

Yikes !! I have never worked with this combination before - so I don't have a known fix for you. When I encounter similar issues, I try to separate things into segments, and work through each segment, until I arrive at a known function.

In this case, I would suggest grabbing a Tach of known good function from your workbench, and wiring it up. It can be anywhere - under the hood / compartment floor / it doesn't need to be mounted. Once you get a usable signal to this test Tach, then proceed to connect to the conversion equipment, and diagnose from there.

Hopefully the answer turns out to be something simple.


Regards,
Taz

[HBHRaing]

Yikes !! I have never worked with this combination before - so I don't have a known fix for you. When I encounter similar issues, I try to separate things into segments, and work through each segment, until I arrive at a known function.

In this case, I would suggest grabbing a Tach of known good function from your workbench, and wiring it up. It can be anywhere - under the hood / compartment floor / it doesn't need to be mounted. Once you get a usable signal to this test Tach, then proceed to connect to the conversion equipment, and diagnose from there.

Hopefully the answer turns out to be something simple.


Regards,
Taz

I actually tied into a coil trigger and ran it through the conversion. Basically to simulate the tach signal from the gm computer. Obviously It's one pulse per 2 revolutions so the rate was wrong, but everything worked. So I know all I'm lacking is the gm pulse. I'll try a pull up circuit to see if that will produce the signal I need, but otherwise I'm stuck. Thanks for the help.

[Taz]

... have an E67 ECM that is being used with an 08 TBSS motor swap ... Our problem is the tach wire. Its been set to the White wire on connector X1, Pin 25 ... the ECM, we found that it was set to serial data, instead of the crank signal that we needed. We set it to Crank ...

Just reread your original post ... something is not right.

Can you post your tune ?

What tuning software are you using ?


Regards,
Taz

[HBHRaing]

We used EFI Live. I do not have the software here. A client opened it up for us. I know it was set for serial, we changed that selection. However I do not recall any other options being edited. I think there were only 2 or 3 fields that could be edited in the tacho section.

[Taz]

Read the tune from the ECM, and post it when you are able. A 2008 TBSS would have been set to PWM from the OEM. Apparently yours was not set this way - so either it has been previously altered, or is not actually a TBSS tune (despite what the VIN may indicate).

Also, the 2008 E67 Tach parameters include "Serial" if using HPT, or "Can Bus" if using EFILive.


Regards,
Taz