My 300zx is cranking, but not starting

[magictk]

I've been reading several links on here where people's cars will not start. A few days ago, mine decided to not start. 1995 na, ~160k miles

http://www.magictk.com/300zx.wmv <-- a video of what it's doing. At about 5 seconds, you can hear the something that seems like the engine fires and kicks the starter out, but the starter kicks back in and grinds. When I remove the fuel pump fuse, I am able to keep it cranking with no kick back.

I did some troubleshooting today and came to the conclusion that I have no idea what is causing it. I did have another car running with jumper cables to my battery, so I know I had plenty of power. Battery is only a few years old. NGK spark plugs were changed back in Feb. Starter, fuel pump, and battery seem fine, so I am guessing it is somehow not providing spark at the right time. I have not pulled the spark plugs to check for spark though.

I measured the crank angle sensor terminals. I have about 5v at the power pin (is this correct or should it be 12v?). In the service manual I found online http://www.300zx.co.uk/tech/manual/manual/efec/106.gif and http://www.300zx.co.uk/tech/manual/manual/efec/107.gif, it says it should be battery voltage. I was able to see some waveforms on the two output pins with my oscilloscope, but my oscope has slow response, so not sure it if truly represented the actual output, which I assume should be pretty much clean square waves. Is my CAS bad?

I did not test my PTU either. Maybe if I have time on Sunday, I will try to measure it. Other than that, I am hoping someone out there can give some suggestions. If not, I will have to have it towed and serviced at a shop. Hopefully it doesn't cost a lot.

[GerryO]

I've been reading several links on here where people's cars will not start. A few days ago, mine decided to not start. 1995 na, ~160k miles

http://www.magictk.com/300zx.wmv <-- a video of what it's doing. At about 5 seconds, you can hear the something that seems like the engine fires and kicks the starter out, but the starter kicks back in and grinds.

Remove the starter and have it bench tested. Once the starter kicks out, it shouldn't re-engage until you turn the ignition key again.

[magictk]

Remove the starter and have it bench tested. Once the starter kicks out, it shouldn't re-engage until you turn the ignition key again.

Gerry,

Thanks for replying. In my brief troubleshooting, I had actually pulled out the fuel pump fuse, and when cranking, the starter never disengaged. I had a friend over when I recorded the video, and he said it looked and sounded like one of the pistons was trying to fire before that piston had reached the top. This caused it to misfire and the engine actually rotated back slightly (which is the hesitation seen at about 5sec) and that caused the starter to disengage. And since I was still holding the key trying to start, it caused the starter to reengage. I am pretty sure the starter is not at fault in this case.

Either way, I am having it towed to the shop tonight and hopefully it is relatively inexpensive, but who knows...

Thanks!

[magictk]

So the shop called earlier and said it was the crank angle sensor that was bad. They will have a part in by Friday and do some further testing just to be sure nothing else is bad. Hopefully that's all that went bad.

[GerryO]

Be sure to get the old part. CAS is still about $300 new? Learned how to take one apart without damaging the thin metal laser cut wheel inside, the hard way, to successfully replace rough/dried sealed bearings inside, but that's another story. Suppose the sensor/pick-up or wiring connections could go bad, or bearing debris could clog cut outs in the wheel. Best of luck.

[magictk]

Ehh... $400

And I was dumb and forgot to ask about getting the old part, but I don't really have time to take apart and/or fix the old one anyways. I am familiar with how optical sensors work, just no time for extra projects.

At least it runs now.