Knock sensor fault - I've run out of ideas!

[drlunch]

Please can somebody help me with this fault!

When starting out in my car, as soon as I reach 3000rpm my engine warning light comes on and the car runs in safe mode for the duration of that journey. A diagnostic check shows this to be error code 52 – knock sensor.

I replaced the knock sensor with a GM knock sensor from GTS Chris. The problem still existed, I reset the ECU to clear all error codes and the warning light once again came on and the error code was 52.

I tested both knock sensors (the original Toyota sensor and the GM sensor) by connecting an oscilloscope probe to the pin and monitoring the waveform whilst tapping the case of the sensor with an object. A sharp pulse was seen on the scope during each tap so I presumed the sensors were working correctly.

I did a continuity check between the ECU pin and the knock sensor with it present in the engine and the link was good.

I connected a portable oscilloscope to the ECU pin for the knock sensor and ran the engine and ensured there was a waveform. This waveform increased in amplitude as I revved the car and appeared to be constant.

The knock sensor first went a while back just before my engine rebuild (my piston rings went). The engine is now running perfectly after the rebuild apart from this fault. This fault appears to be intermittent. Sometimes I can drive the car and the warning light does not come on for the whole journey, other times the warning light will come on as soon as the car reaches 3000rpm.

I would really appreciate any idea or thoughts on how I can further diagnose or fix this.

Car = 1996 Rev4 GTS Turbo

[AM TUNING]

if u have checked the knock sensor and the wiring all it can be is the ecu

[Goldy]

Erm sounds like a silly question... but have u actually checked that the engine isn't knocking? Can you hear any knocking?

What fuel are you running?

[drlunch]

I've always used Optimax since i've had the car. I can't hear any knocking. I thought that the knock sensor was supposed to deal with any knocks by adjusting the timing accordingly not by flagging an error and then completely retarding the timing. I'm not sure though.

[Mike_2t]

Have you checked the loom going to the KS, could be a corroded wire or faulty connection..

[BenF]

I've always used Optimax since i've had the car. I can't hear any knocking. I thought that the knock sensor was supposed to deal with any knocks by adjusting the timing accordingly not by flagging an error and then completely retarding the timing. I'm not sure though.

That's not a safe assumption - sounds like you lost the last ringlands due to detonation (knocking)

The ECU will wind back the timing as far as it can go and cut boost (on rev1 and 2's) to protect the engine.

I'd take the car to a known good rolling road and get it checked out. Its quite possible that something like the timing is too far advanced for the boost level you're running which is causing the problems.

Knock sensors are quite fragile - you've got to tighten them up very gently onto the block to stop them breaking.

It sounds like you have done all the right things though to check it is working - the only thing you can't tell is what the amplitude of the output signal of a 'good' knock sensor should be.

The 'limp' mode you describe sounds very much to me like the ECU doens't think its hearing a signal from the sensor.