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MoTec M84 and Transmission Controller Communication

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Hi everyone,

I'm looking for some technical advice regarding the communication between a OEM ECU, MoTec M84 and OEM Transmission control Module. I have an EL Xr8 Falcon which is stuck in a limp mode and will not shift out of 3rd gear. The gearbox was shifting when the MoTec and OEM ECU were sharing the sensor 0V sensor lines, and half of the tune was completed however it is stuck in limp mode now and unable to shift. Attached is some photos of the TCM and ECU wiring showing how they require data from each other to figure out shifting modes. It appears that the TCM requires Throttle position, engine temperature, engine speed, vehicle speed, trans temp and gear position to operate correctly.

Currently the MoTec is using a separate coolant and air temperature sensors and the engines TPS (There is also another TPS for the TCM and I've tried swapping them around - and no go) . The trigger wiring is the same as the attached Ford Narrow tooth drawing with the REF signal spliced and going straight to the RPM signal Pin 6 on the TCM. (This did work and shifting was momentarily operational). I have also tried a pull up resistor going through an auxiliary input, which also displayed a working tacho but no gear shifting.

I have made a flash code reader and the code shown is 'Engine speed'. With the MSD Distributor outputting a 12V signal (refer the attached scope) do I need some type of filter going into the MoTec?

Currently we have tried the following parts

Inhibitor Switch

Refurbished TCM


Any help would be greatly appreciated!!



Attached Files

I bet the TCU is looking for a standard tacho signal, not the REF signal from the crank trigger, what does the factory workshop manual say about that?

Thanks for your reply David. The manual states for the Engine speed sensor fault flash code:

'The signal from the ignition of ignition pulses has either been non-existent when it should have been there or else has been unreliable. There are 2 reasons this faults could occur. One due to the lack of ignition pulses when other TCM inputs are present. The second cause is the frequency of the pulses on ignition pulse input to the TCM indicate an unachievable speed of greater than 7000RPM".

So, it is a tacho signal you need to supply, not the crank reference. That is why the frequency is too high. It wants to see 3 pulses per revolution, not however many teeth are on your crank trigger wheel.

Thanks David I will try swap the tacho signals and see how that goes

Just an update - Still no shifting present with the tacho wire pinned to an auxiliary output with a pull up resistor. I have also tried splicing this wire to the EEC (ford ecu) also however no luck. The manual appears to have an internal connection from the negative coil to the tacho pin...does the factory computer process the negative coil signal and send it out through the tacho line into the TCM?

Going through the factory pin out photos I've attached, to run this as a piggy back having these ecu's running separately would be ideal right? using only the sensors required to run the MoTec and all others separate. Or is there a different way to communicate 2 ecu's and a TCM?