What Happens When A Knock Sensor Plays Up?

[jakez88]

hey guys been looking through some threads and all i have gathered about knock sensors is that they do something with the timing and there is 2 of them in a r32 gtst?

why 2 of them? do i need to buy 2 if 1 is faulty? where are they? what happens when one or both plays up?

basically i got my car checked out today because of a problem that i have not yet been able to figure out. have a r32 gtst that has power cut outs randomly and then jump back on after that. otherwise the car runs fine. if i'm idling and it happens it'll make the car stall.

got it checked out and hooked up to the computer and it came up with the knock sensor error? they said to replace the knock sensor but would it also be that something else is making the knock sensor error come up or is contributing to it?

anywhere on the forums i can get a new one? how much are they usually?.

thanks!

[jakez88]

anyone?

[SteveL]

hey guys been looking through some threads and all i have gathered about knock sensors is that they do something with the timing and there is 2 of them in a r32 gtst?

why 2 of them? do i need to buy 2 if 1 is faulty? where are they? what happens when one or both plays up?

There are two because one does cylinders 1-3 and the other does 4-6. They are screwed into the block 'underneath' the inlet manifold just below the head gasket line, roughly in line with cylinders 2 and 5. If they trip an error in the ECU it will limit or fix the ignition timing advance in what's called the 'knock control region' (KCR) of the ignition timing map. It's done to prevent engine damage.

if i'm idling and it happens it'll make the car stall.

Ignition timing at idle won't be included in the KCR, which might suggest you have another problem entirely.

Did you clear the ECU error codes, run the engine again (ie drive it for awhile) and then recheck the error codes ?? You should always follow that procedure to ensure that the error code isn't simply transient. Even if you did follow that procedure, the first thing you should do is check all the wiring and knock sensor connectors for damage or even simple disconnection. A knock sensor is basically a PZT, which are very simple and robust devices and while it is possible for one to fail, that's pretty uncommon. Testing is not simple and requires access to an oscilloscope to be absolutely sure, and even then there's a bit of interpretation required. Substitution of a known good one (or pair) is usually quicker. A new one from Nissan is probably at least a few hundred $$.

[jakez88]

^^nice thanks mate. so if it is another problem, what does the problem sound like to you guys?

[MrStabby]

The ECU has knock timing map and knock fuel map. When knock is detected the ECU uses those maps, which have more fuel and less timing. The normal and knock maps are also known as the premium and regular fuel maps.

A knock sensor error indicates the sensor is broken and that is a different thing to sensing knock, which is a normal thing for the sensor. Its likely that the ECU takes the conservative approach and uses the knock maps if it cant get a reading from the sensor. Ie it assumes worst case as its preferable to risk inefficient operation than risk motor damage.

So check all the wiring, and if there's no breaks or shorts its probably time to change the sensor(s). Or take it to a pro and get it properly diagnosed.

[Rekin]

Occasionally my ecu picks up knock sensor error but then clears it self, not sure why exactly it happens. Here is a scan from the rb20det manual, it could help in the diagnosis of your problem