Good evening I have a 1995 Jaguar XJ12 with a 6.0L V12. I will be running a universal ECU and was curious as to why it has 2 crank sensor. One at the flywheel and one at the front pulley. When this car was built was it running under two ecu's like having two six cylinders instead of running as a V12?

 

The Denso ECU may have been built to only handle 8 cylinders as a max for other cars

A specific chip in the ECU to handle 12 cylinders may not have been available

To put 2 chips on the motherboard may have been physically impossible with the already routed circuit lines and to redesign the motherboard to accommodate 2 chips would be economically prohibited based on the number sold or the engineering manpower present to do so

Just guessing

 

The FRONT sensor is the crank POSITION SENSOR.
The REAR sensor is the crank SPEED SENSOR.

The engine will run (but not well) without the speed sensor but will NOT start without the position sensor.

I had a car in the shop for poor running. The sensors both have the same part number so I swapped them.
The bad sensor (speed sensor in the rear) was moved to the front and the engine would not start.
I replaced the front sensor and the engine ran normally.

The flywheel sensor just counts teeth. The front sensor has segments and spaces to determine position.

bob

 

A 95 XJ12 shouldn’t have one at the crank, it should be on the right cam shaft. But in either event, the purpose of two is for one to time the other. Cars with just one have a gap at TDC, but the Jag V12 is sensing flywheel teeth.... and there is no gap. So it needs a second signal for TDC.