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OEM Z32 detonation (knock) sensor. Fits all 1990+ Nissan 300ZX models.
This sensor is a "microphone" through which the ECU listens for pre-detonation or spark knock that can cause engine damage. In the event that the ECU "hears" detonation it pulls timing and adds fuel until the detonation goes away but it does not generate a diagnostic trouble code. Unfortunately the Z32 ECU does not "listen" for detonation at higher RPM, as it is not able to distinguish detonation from other engine noises.
A diagnostic trouble code 34 generated by the ECU means that the circuit for the detonation sensor is broken, not that the ECU has "heard" detonation. The ECU is always looking for a resistance in the detonation sensor circuit of around 1 mega-ohm. If this resistance is not present the ECU throws a code 34 and also goes into a self protection mode in which ECU switches to more conservative safety maps with less timing and more fuel as well as lowers the boost level on Twin Turbo models by opening solenoids that normally bleed off some of the pressure to the wastegate actuators. The faulty part in the detonation sensor circuit is usually the sub-harness between the sensor itself and the EFI harness. Corrosion on the terminals of the connector between the sub-harness and the detonation sensor is usually the cause of a code 34. Z1 sells the detonation sensor sub-harness HERE, you can select to add one for a discounted price below. Now that Z32s are surpassing 20 years old, this system that was designed to help protect your engine from damage from things like low grade fuel often fails and results in poor performance and fuel economy even though there is no detonation taking place.
The detonation sensor is located on top of the cylinder block in the valley between the heads under the intake manifold. It is difficult to change or even clean the connections on unless you have your engine apart. It is possible to eliminate a code 34 by tricking the ECU into believing the circuit is OK. You can attach a 1 mega-ohm resistor across the two terminals in the plug that attaches to the detonation sensor sub-harness on the main engine EFI wiring harness. Z1 sells a plug in type of this resistor HERE. This will eliminate the Code 34 allowing your ECU to function as normal, but will eliminate the self protection function of the detonation sensor altogether. Nissan included the detonation sensor for a reason, so it's not recommended to eliminate it unless you are clear on how to minimize the risks.
Normally the detonation sensors do not fail unless they are broken or melted as a result of overheating the engine. The plastic casing begins to liquefy around 250 degrees F. So this is a helpful indicator if an engine has been overheated or not.
We do not recommend the cheap detonation sensors found on E-bay local auto parts stores and the like. These cheap aftermarket reproductions seem to be incapable of picking up the proper frequencies required to identify detonation.
Upgraded Knock Sensor Sub Harnes: