Fusible link after replacing head

[nando]

The connector beside the CPS connector is for the Cylinder ID sensor (on the #6 plug wire) and is used for timed sequential injection. The tachometer signal is generated by the DME from the CPS data.

An M20 engine does not have a camshaft sensor.

I didn't want to reply to this when I was on a phone as it deserves a more detailed reply, but I respectfully disagree, on a technical level.

First you have to understand what a cam sensor does (not saying you don't jlevie, just explaining in detail). It does NOT detect engine RPM. Even modern cam sensors have too few teeth for them to be used reliably for crank angle/RPM calculations. It also turns half as fast as the crank, making the resolution worse.

What is a cam sensor's primary and most important purpose? Detecting engine phase! Figuring out if the engine is on the intake or exhaust stroke so that injectors can be timed to the opening of the intake valves (and individual coils fired if present).

And that is exactly what the CID sensor does - it might not actually have a sensor directly on the cam, but functionally it's identical to a single tooth cam wheel which is all you need for full sequential fuel and spark (in the M20's case, there aren't enough transistors for full sequential, but it does run in a semi-sequential timed injector firing).

the CID is actually pretty clever and effective - the only reason it's not used after the M20/M30 is it requires a reading off a fired coil, and you can't get that unless you time the sparks correctly - which is possible with an electronic distributor because the firing order is "fixed" by the cap/rotor, but not with a COP setup where you need the engine phase before you can fire a coil. Sort of a chicken & egg problem.

More modern cam sensors will have more teeth, but that is primarily so they can start and enter sequential fuel/spark faster; they still aren't used for RPM detection. On engines with variable valve timing they can detect cam angle but are still never used for RPM detection. the crank sensor is used for that as the resolution is many, many times higher (and on modern high efficiency engines, accuracy counts).