Nissan Repair: 84 300zx & 80 280zx, crank angle sensor, 84 300zx

Question
I am an experienced "Z" owner and driveway mechanic.  My 84 300zx non turbo automatic 4 seater is in limp mode.  I have run a code check and get multiple codes.  My Haynes manual suggests defective crank angle sensor and describes how to R&R, but not test.  Can you advise how to test?  Can these be purchased without having to buy complete distributor?

Also, my 80 280zx automatic non turbo t-top coupe has been burning out internal voltage regulators.  I have the alternators professionally rebuilt by a well respected local auto electric shop.  They work for about 5 to 20 minutes before failing.  The car runs until the new battery runs down.  Could a faulty headlight switch, a/c motor, or aux fuel injector cooler fan motor cause this problem?  I have serviced the headlight switch and the a/c motor seems okay.  I don't recall ever hearing the aux cooler fan come on and I don't know how to safely test it.  The voltmeter warning light displayed on the first two failures, but isn't lighting up this time.  The gauge seems to be indicating correctly.

Answer
Larry,

The way you test the crank angle sensor (optical pickup and receiver) is to get a volt/ohm meter and check the oputput signal.  It should be a distinct square wave.  That is there are going to be six distinct pulses.  I find the distributor to be bulletproof in the optical pickup and receiver electronics so I rarely test them.  What I find most often is the oil seal fails in the distributor.  An engine with many years and miles usually has oil blowby.  That is, the compression rings are leaking and this translates into crankcase pressure and this eventually overcomes the seal in the distributor.  The oil seeps through the distributor seal and walks its way up the shaft and eventually the optical shutter wheel and the optical pickup and receiver get coated in oil and the normal square wave that is generated gets interrupted and that means the engine runs strange to include what you describe and the codes you indicate.  I have experienced this on many Nissan cars over the years and it is usually once they get around eighteen years or older.  Some do it sooner depending on the oil change intervals.  Also, you could use Restore and Mobil 1 5W30 in an oil change to get the rings to bite more and increase compression adn decrease blowby with the rebuilt distributor you need to install.  Not worth doing the rebuild youself due to the expense and in the case of distributors I purchase a rebuild from Nissan only.  Aftermarket distributors are not worth the trouble I have experienced.  Check out courtesynissan.com for a good deal on a rebuild.  The dealer will be much more...

On the 280ZX, and I must say I envy you since I miss mine so much, I would be looking at the basics first.  Check the battery cables first and the starter circuit.  Make sure the alternator is connected properly and nothing is touching ground.  The only way an alternator is going to run away and put max voltage is for the regulator to command it.  That is, the wiring is wrong or one of the plastic insulator washers is out of place or the external wiring is feeding directly to ground.  I say the above since you say the battery will run the car after the alternator kills the regulator.  I had a 280ZX that I loved and it was stolen.  The police recovered the stripped car and I put it back together.  The alternator harness I procured from a wrecking yard was shorted inside and I ended up going through two alternators before finding the problem...  Check it out and email me back with what you find.  Nothing else on the car should take out an alternator other than the switching and charging circuit to and from the battery, alternator and starter.  You can get an inductive ohm meter to test independent circuits for about $20 bucks.  The inductive part is nice since you do not have to run it in series.