Need proper pin on ECU for Idle check

Tach not woking where do I check for proper connection to send data to the Tach.??

Thanks

Sloth

Sloth,
What model year is your XJ-S and what engine does it have?

Paul

There is a wire from Ignition amp to Tach that provides that signal (looks like earphone jack).
The other wire from Ignition amp to ECU provides RPM to the ECU, but that doesn’t drive the tach (looks like spade connector)

Greg,
I agree that is how the Lucas system works, but the Marelli ignition system is different and I have no idea how the later non-V12 cars work. We still have no idea what model year and engine this post was about.

Paul

also a bit confusing, as the title and question are very different

Greg,
Yes, I agree. He just replied to an existing thread that had nothing to do with his issue or question.

Paul

Hi PAUL:
My car is '89 XJS …and I took your advice and redid the butterfly valves to .002 and my car does idle, a bit fast., The large air control bolt on the AAV did bring it down a bit but still not quite calm enough.

Sloth,
Ok, 1989 was the transition year from the Lucas to Marelli ignition. Which one do you have? The tachometer signal feeds are different.

If your idle is still too high try closing off the throttle butterflies a little more to see if that helps. 0.002 inch is a tiny opening and one that I have difficulty setting and measuring. So I get it close with a feeler gauge and then close both of the butterflies together one flat of the bolt head at a time until I get it to where I can use the bolt on the AAV to set the idle to spec.

Paul

He might also have a vacuum leak somewhere.

Kirby,
He could also have a dirty throttle body, broken or missing throttle spindle bushings, or a partially stuck AAV, but I like to try the simple, likely, and inexpensive things first while troubleshooting and then when I know those are OK then move to the more complicated ones. Finding a vacuum leak can be a challenge.

Paul