I recently had a customer come into my shop with a 1993 300ZX 2+2 non turbo with automatic transmission that had a drivability problem. He had been to a few shops including a Nissan dealer and a transmission shop for loss of power and stumbling during acceleration. Their numerous attempts to cure the problem by swapping out parts and other "shotgun" solutions failed.
Our basic engine analysis found nothing but very retarded timing. At this point we turn the cam sensor all the way for advancing but the timing gun still shows it firing at 0 degrees instead of 15 degrees before TDC. A jumped timing belt link was the first thing on my mind but no luck. We dug a little deeper and found the cam sensor interface shaft all chewed up. I reviewed all of my service releases, and the following symptoms were pretty close to what we had encountered.
Some 1990s two-seater, 2+2 and turbo 300ZX models may suffer from detonation because the base timing gets advanced. Trying to reset it by adjusting the crank sensor may not work because the camshaft indexing peg may have been damaged. Some cylinder heads on these cars were improperly machined, which can lead to the peg taking too much load and eventually failing.
Nissan says you have to replace the head (part# 11091-40p80) in order to correct this condition. You'll probably need a new camshaft (part # 13020-F6515) and crank angle sensor (part# 23731-45V10) too. We have serviced literally hundreds of Z32s in the past few years, but this is the first time I have encountered a case of Nissan's poor manufacturing, especially in a case where the vehicle is well maintained and has less than 50,000 miles. I hope this is a very rare case and it that is does not happen to our Z Club members.
First printed in Z Club of Houston Exhaust (June 2004, Vol. 30, Issue 2).