Engine Speed Sensor(s)?

[kman0066]

Background: I have a 2004 M1097A2 that came with a 6.5L N/A and 4-speed. The block date codes as a 99 6.5 GM, non-GEP. I've just removed the motor since it blew-up and I am working on swapping in a Turbo 6.5 from another HMMWV. It did not come with a Tach.

Issue: I had read that I would need to move the engine speed sensor wires, but now looking at the old 6.5 N/A motor, it has the CPS sensor on the front of the engine and the yellow engine Speed Sensor on the back of the engine. The CPS sensor plugs into the engine harness and the yellow speed sensor plugs into the body harness near the bellhousing area. Everything I read seems to be that there would be one or the other, so I'm confused on what I need to do. Since the Turbo motor doesn't have the rear speed sensor, just leave it off? Or will it need a jumper in the rear connector if removed? Or are the jobs of the 6.5N/A CPS different than that of the Turbo 6.5 and I need to cross some wires here? I've looked through the wiring diagrams in the TM and don't see any diagram showing both sensors on the vehicle at the same time and so I'm not sure what's going on.

 

[Mogman]

Welcome to the SS forums!!

 

[kman0066]

OK, I think the front CPS sensor is what the transmission uses and the rear engine speed sensor is only for the diagnostic port. It seems odd to run 2 different sensors for this. And why this isn't represented in the TM or wiring diagrams is a mystery. But I think if my hypothesis is right, that means the rear sensor is basically pointless other than for troubleshooting via the connector in front of the shifter, and seeing as I don't have any interface for that anyways, it can just be deleted. I guess I'll find out once I get it all running/driving if I'm right...

 

[Mogman]

OK, I think the front CPS sensor is what the transmission uses and the rear engine speed sensor is only for the diagnostic port. It seems odd to run 2 different sensors for this. And why this isn't represented in the TM or wiring diagrams is a mystery. But I think if my hypothesis is right, that means the rear sensor is basically pointless other than for troubleshooting via the connector in front of the shifter, and seeing as I don't have any interface for that anyways, it can just be deleted. I guess I'll find out once I get it all running/driving if I'm right...

You've got it! The rear sensor came about for diag with the 6.2L which did not have a crank sensor so that continued until the center mount turbo made it impossible.

 

[kman0066]

You've got it! The rear sensor came about for diag with the 6.2L which did not have a crank sensor so that continued until the center mount turbo made it impossible.

Awesome, thanks for the confirmation! Appreciate it.

 

[Gcelevator]

Body lift to fit the turbo engine, engine wire harness is routed in a different direction, speed sensor, justvthe one in the front ( i don't remember if i had to cut and splice) and probably TCM ( i am using the same for the 6.5 NA)

Good luck