Diagnosing no spark on 1991 300ZX

[IceZ]

In my searches through the forum I didn't find any thread addressing this issue comprehensively, so I've tried to assemble some of the info which has been useful here.

I bought my N/A '91 300ZX last month. This week brought it to my mechanic for a transmission seal replacement and a tuneup. Picked it up Wednesday and have been driving it daily since. Late last night on my way home I took off from a stop and accelerated fairly strongly through first, second, hit third and got up to about 5,000 RPMs and the engine died - straight from 5K to 0, no chugging or anything. I coasted onto a side street and attempted to restart the car with no luck. The car turns over (cranks) but does not start. Also, when the engine died my aftermarket stereo head unit froze/shorted, so that even with the ignition in the off position the stereo display was on. I had to unplug the whole head unit to reset it. I don't know what this has to do with the problem, but it isn't normal.

What I've learned so far:

• My gas gauge put me below 1/8 tank, so I added 2 gallons of gas, just in case. No such luck.
• Cycled the ignition from OFF to RUN position multiple times and listened for fuel pump priming - last night my pump primed a few times intermittently, today not at all.
• Checked ECU codes) - it threw a 33 (left exhaust gas sensor), 34 (detonation sensor circuit) and 53 (right exhaust gas sensor). I didn't check codes before, so don't know if 34 is new, but from what I read it shouldn't kill the engine entirely.
• Googled "300zx no spark" and read Vilmenay's advice about diagnosing a no spark issue:
• Checked for spark by pulling a plug and grounding it against the intake manifold - no spark.
• Checked for power to the coil plug with a multimeter (need ignition in the RUN position for this) - there are 12 volts of power to the middle lead on the wire harness.
• Loosened the three bolts on the crank angle sensor (here's an image of a crank angle sensor on a 300zx for reference) and rotated it back and forth - not hearing injectors firing or fuel pump priming.

From the information I've read so far, it sounds like this could be a PTU or CAS problem. Is there anything I'm missing?

[davidp94]

I've had the engine completely die on me too. Not fun. Have a look at the CAS connector. First make sure its on their (in my case, it broke off) and secondly make sure its clean.

Also, do you have the new style PTU? You'll know if its the old if it has fins on it. PTU is located on the passenger side timing belt cover (i.e., factory location). The old style were prone to failure resulting in no start and/or no spark conditions.

If you have the new style PTU, make sure the connections on the sub-harness (if it hasn't undergone an sub-harness delete) are properly connected and that none of the pins are backing out. The sub-harnesses were also a area of failure, subject to corrosion.
Unfortunately, I get the feeling I've told you things you already know.

[IceZ]

Thanks for the reply, davidp94! It was the CAS connector - mine had just shaken loose. I pushed it back in, ran some electrical tape around it to keep it on and it started right up.

[nexus08]

Got to love these cars!

[Ziggy1621]

Welcome to Nico, glad you got if figured out. Check out the Classifieds section and see if you can find someone selling a CAS so it doesn't happen again. A lot of times you can find them fairly cheap, and NA/TT CAS are the same and will fit your car, as long as it is the old style CAS