SonySC up on blocks again

I've been busy working on my son's 280Zx turbo for the past few months. I need to get the SonySC running again to rergister it and Smog. She was running rough and when fired up would run on 3 cyl, showing a lower Tach indication, then finally clean up and the Tach would jump back up where it would belong. Then she showed a loss of vacuum and quit completely.
I suspect the Crank Sensor as everything else was replaced 20k miles ago when I had Bob Johnson rebuild her. It tries to start but runs like she is out of time.

Does anyone have the article about changing the crank sensor?

Also does anone have a spare 92 Auto EEC , or any other sensors, etc I could borrow to try to prove what is wrong?

by the way I have a bunch of extra SC parts including Jim Ds old Pro M air inlet and tube if anyone needs em.

I'm in Danville if anyone has a few minutes to stop by.
Thanks George Clarke aka the SonySC

That isn't the crank sensor. A bad crank sensor would not run at all. When the tack drops completely that is typically the cam sensor but if the tach drops out by a 1/3 then that typically points to the DIS. Either the DIS or the cam sensor will give similar running symptoms. I keep a spare of both parts on hand at all times because it is easy to swap both items to isolate a problem.

Before replacing any parts, make sure all harnesses are clean and tight and that your harness shield grounds are properly connected and functional. The cam sensor, crank sensor, and DIS wires are all shield protected circuits.

XR7 Dave said:

That isn't the crank sensor. A bad crank sensor would not run at all. When the tack drops completely that is typically the cam sensor but if the tach drops out by a 1/3 then that typically points to the DIS. Either the DIS or the cam sensor will give similar running symptoms. I keep a spare of both parts on hand at all times because it is easy to swap both items to isolate a problem.

Before replacing any parts, make sure all harnesses are clean and tight and that your harness shield grounds are properly connected and functional. The cam sensor, crank sensor, and DIS wires are all shield protected circuits.

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Dave has hit the nail on the head here.

Have you checked the car for any codes?? Check eng. light on??
I would go with the Cam. sencor or DIS myself also.

Kurt