Knock sensor fault

[Paul Firth]

I keep getting a code 34 so decided to fix the problem once and for all. The code only appears if the car has been on boost and you can feel that something isn't right. I've already checked the sensor and the resistance was spot on, so I checked the input at the ECU at idle and it was between 2 and 3 volts as it says in the manual. I decided to go for a drive with the voltmeter connected to see if it changed under boost. The car was back to its old self again, much faster and I could tell the problem had gone before I'd even checked for the fault code, which wasn't there. But as soon as I disconnected the earth probe of the voltmeter it went back to how it had been and the fault code came back. So I'm now thinking that there is something wrong in the wiring, possibly the screening wire, and the input wire being earthed through my voltmeter is somehow sorting the problem. Unfortunately I know very little about electronics and don't know what to try. Does anyone have any suggestions on what to try next?

 

[Fast Guy]

I believe there's only one wire to the det sensor, so if you're feeling brave you could always run a new wire from the ecu to the det sensor and see if it fixes it. I wouldn't bother until you're very sure it's down to the wiring tho.

 

[Paul Firth]

There's only one wire connected to the sensor, but there's a screen wire around that wire which goes to earth at the two connections on the inlet manifold. It's right next to the knock sensor wire in the plug between the engine harness and EFI harness (F7 and E222 in the wiring diagram), but I don't know how to test it. Now I've noticed how much power it's robbing I'm going to fix it if it means rewiring the whole car!

 

[Paul Firth]

I've heard of a few people saying that they've replaced the sensor and the fault was still there. Hasn't anyone ever fixed this fault?

 

[Anonymous]

Typically the knock sensor only fails from excessive detonation. It doesn't die with age or anything like that. If you've killed two sensors in a row then first I would check

1) You are torquing them up enough and they aren't coming lose
2) That you don't EVER drop a knock sensor. That will kill it instantly

Remove the faulty sensor and check for continuity from the sensor body to the plug connection. You should have some, if you don't it's duff.

If your first sensor failed because of bad detonation, and you put a new sensor on, boost, still suffer from detonation, then you'll kill the new sensor off just as quick. First find out why the original sensor failed before killing any more the same way.

 

[Anonymous]

And having just read your post properly this time! If the sensor is ok, then it'll just be a wiring fault. You only need to run a new signal wire to the sensor, the screen wires aren't really required.