| In my quest to cure a very annoying safety boost condition (thought I was experiencing detonation but was not) I have learned a lot about the factory knock sensor, and how important it is to the optimal functioning of the 1990-96 300zx TT. Mostly I have discovered how wrong-headed (and potentially dumb) it is to bypass the detonation sensor. Almost any Google search for "300zx knock sensor" will result in the instructions for how to bypass the sensor, and tell you how "useless" and "unnecessary" it is. Nothing could be further from the truth. The ECU in our cars is far more advanced than people seem to give it credit for. It was way ahead of its time, just like the rest of the car (which is why we love them). The knock sensor is not just there to prevent detonation from destroying the engine, it is used by the ecu to fine tune timing advance for optimal power and economy. The ECU advances timing 0.101° every 100 ms until it detects knock, then it will retard timing 1.199° for each cylinder that is knocking. (ref- [ http://twinturbo.net/nissan/300zx/forums/technical/view/1127497/Z32-Knock-Control---Do-you-know-your-ABCs.html ]). It is constantly adjusting the timing advance, and needs a functioning knock sensor, in the factory location, to accomplish that. Also if I read one more post where someone says "The knock sensor doesn't work over 3200 rpm" I will start screaming. It actively works up to 4400 rpm, but apparently still does do something over that, within the limits of the system. You may think that because you did the resistor trick to bypass the sensor and your car seems to run fine, that everything is great. But all you are doing is letting the ECU push timing to its maximum advance, with no way to monitor if this might be causing detonation. If you do not run high boost, and always use 91+ AKI fuel then you may get away with it. But what happens when you start getting a little carbon buildup on your piston crowns? I don't regret paying my mechanic for the time it took to pull the plenum and lower intake so the knock sensor could be replaced. If you can do that yourself, great. Otherwise, start saving. Anyway, it appears my issues with safety boost appear to have been caused by a broken shielding wire for the knock sensor sub-harness. As the sensor generates only a tiny amount of current using the piezoelectric crystal and uses a single wire to carry it all the way to the ECU it is very susceptible to RFI, so the integrity of the shielding is critical. Otherwise your ECU starts adjusting timing (eventually switching to low octane fuel maps and turbos into safety boost) even when you have no detonation occurring. I hope this helps clear up some of the confusion and just awful misinformation out there. And that if you found this post using Google that you will get your car fixed correctly. Mark
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