I have run into this issue a few times when on the dyno on a few cars. Basic set-ups are DIYPNP's and Toyota COP's. When on the dyno the tach signal being picked up through the inductive wires on the dyno is weak. Some days are better than others, but I was looking for ways to correct or boost the signal to try and help the issue. I tried adding a capacitor to the COP harness and the car fired right up and seemed to idle smoother, but the tach signal in the cluster was gone. I am running a resistor in the diagnostic box, would adding the capacitor to the COP's and removing the resistor restore my tach in the cluster?

In order to keep the capacitor and have a tach, I may have to rewire the tach signal to come from the Megasquirt instead of the Toyota coils.

Does anyone have any other suggestions to avoid the dyno having trouble picking up our tach signal?

 

Use an old plug wire. Jam the coil end into the cop. Not good for dailying, but good enough for easier inductive pickup for a timing light.

It sounds like you added the cap to the wrong spot. Adding a cap to the diag box is not how electronics work.

 

Not sure why you think that I installed the capacitor in the diagnostic plug. I know where the capacitor goes, and it is not the diagnostic plug.

 

Eh, fair enough - read it too quickly. But if the last thing you added was the capacitor, then logically, you lost your tach because..

 

I used that set-up when adjusting latency also, as I suspect a time delay between the primary signal and the actual spark. Would not matter at idle, but could at high RPM.