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Help with Knock Sensor


pixelplay

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I have my car running now but I am randomly getting a check engine light coming on and off, the code generated is for the knock sensor. Its not always on just every now and then.

When I got the car it had two knock sensors connected to the engine, one was under the manifold in a difficult to get to position and was disconnected and the other one was just up from there and was connected. When i removed the manifold I removed the disconnected sensor and moved the one that was plugged in to where the disconnected one had been under the manifold.

Because the check engine light is not on all the time i am now unsure if the sensor is faulty or the lead to it is maybe not a good connection of maybe I have the sensor in the wrong place as i have no idea where it should be on the engine.

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Cheers Ross, that's where it was originally but because it had another one mounted under the manifold that wasn't connected I thought that somebody had been lazy and disconnected the old one and mounted a new one in a more simple to get to place. I will see if I can remove it and add it back where it should be.

I have also noticed that there is a loose plug on the side of the auto trans that's going to nothing not sure if its how it should be but I cant find anywhere it should plug into.

One other question I have is regarding my boost of the primary turbo as it seems hit and miss. Sometimes it really good and other times its feels like it not kicking in properly. Could the BBOD box cause this sort of thing as its the only area that i haven't replaced pipes so far. I read that there are lots of solenoids that can get dirty and play up.

I have run the engine diagnostics though and don't get any other errors aside from the knock sensor. I also pressurized the manifold when i was looking for leaks and had nothing major leaking. I guess it could just be a sign the turbo is getting old and is due for replacement or rebuild.

By the way that engines looking mint in that pic I think if i stay in NZ long term I will buy a better condition sub and rebuild the engine fully like that. I would love to pull an engine and have a really good play with one now I have got started ;)

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Cheers guys I will sort the sensor and check the solenoid also It felt a lot like the timing is retarded when the engine light comes on and i suspected that that was happening. I think I will just price a new sensor as getting to its a right pain in the backside and it would be a lot of work to change for a second hand one to just have it fail again.

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regarding the knock sensor, just general info - check it for cracks as water/rust will kill the insides. also the metal base of the sensor should be clean (and mating surface) as that is the electrical return through the engine block.

the knock sensor has always been my achilles-heal as it always seems to pick up too much noise from exhaust/piston slap or whatever else is going on <- not at all backed up, really should spectrum analyse the knock signal one day..

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Yeah it would be good to see whats its actually hearing and doing to decipher the sounds from actual knock. Mine I think might just be dirty as the engine was dirty as anything when I got the car and had leaked like a colander under the manifold due to numerous rust holes in piping that's now been replaced. I will have to pull the manifold again but this time I think I will do myself a favor and remove the primary turbo first.

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  • 4 weeks later...

Well I finally changed the sensor today after thinking about doing it for the best part of a month. It was full or hairline cracks and as soon as i put the new one in the check engine light never came on again. the car runs way better and is no longer farting around when driving. The CEL used to flash on and off quite a bit and very randomly retarding the ignition when I really didn't need that to happen.

I believe the knock sensor is tuned to listen for the frequency of pings from the engine, when these are encountered the EUC decides if the noise is important and if it thinks it is it will retard the ignition. The torque of the bolts apparently important also, as if its not torqued properly it will change the frequency that the sensors able to listen to and give false readings making the car run poorly.

 kamineko said:
regarding the knock sensor, just general info - check it for cracks as water/rust will kill the insides. also the metal base of the sensor should be clean (and mating surface) as that is the electrical return through the engine block.

the knock sensor has always been my achilles-heal as it always seems to pick up too much noise from exhaust/piston slap or whatever else is going on <- not at all backed up, really should spectrum analyse the knock signal one day..

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