Will a 5V Sine wave work on an MJ Tach?

[Warren99]

So my gauge cluster's tach is for a 4.0, and I mated a mercedes diesel to my ax15. It has a crank position sensor built into the block similar to the jeep one that goes on the bell housing which I can no longer use with the adapter plate I have on. I'm wondering if I can just simply hook up the jeep wire to the mercedes crank position sensor. According to some people the mercedes cps works off of a 5v sine wave. Is that also what the jeep uses? If not how can I convert it?

 

Also I could very easily just hook it up and see if it seems to work. Not sure if that can somehow risk damaging the tach, but if it's risk free I'll just try it. Thanks

[Eagle_SX4]

The tachometer gets it info from the ignition control module not the CPS. 

 

[Warren99]

On 10/10/2025 at 11:25 PM, Eagle_SX4 said:

The tachometer gets it info from the ignition control module not the CPS. 

 

 

Still trying to wrap my head around a few things, does the ICM modify the signal that it gets from the crank position sensor? Because if not maybe I could just ignore the coil and wire straight from the crank position sensor to the tach.

 

Also still wondering if I can just wire it up and see what it does without risk of it causing damage to the tach. I'd assume it wouldn't cause any damaged and would just give bad readings but I don't know how the tach works in detail.

[Eagle_SX4]

16 minutes ago, Warren99 said:

Still trying to wrap my head around a few things, does the ICM modify the signal that it gets from the crank position sensor?

As far as I know the only thing the CPS does is tell the computer where the engine is at in the rotation. It does not give any signal to the tachometer. The tachometer runs off the pulses from the coil. It just happens to go through the ICM first.

 

As you can see in this pic the sync signal (CPS) only goes to the ECU it shares a ground with the ICM but no information is sent to the CPS from the ICM.

[Ωhm]

No, if my understanding of this circuit is correct.

 

CPS creates AC sine wave. This AC sine wave lives within a 4.1vdc world on the ECU. Using Analog to Digital converter, AC sine wave (analog in) is converted to pulsating DC square wave (digital out). Now the ECU can count these square waves and determine exactly where crankshaft (piston) is. Based on a certain number of counts (4cyl/6cyl), ECU will then send a square wave to the ICM and fire the coil. In return the ICM sends a square wave to the IC Tach (gauge). Tach then counts the square waves over a certain amount of time and displays the engine RPM’s, always repeating this process.