Will a faulty knock sensor cause false knock?

[Sheik Jabooti]

Does anyone have any experience with a faulty knock sensor causing false knock signals. I get knock at low rpm low-mid load but nothing at high rpm. It's so bad that it retards the engine timing.

I've taken it to a couple of mechanics and they reckon they can't hear any knock. The car sends loads of knock signals even in idle.

I'm not sure if changing the knock sensor will be a $300 pointless exercise or worth doing? Any opinions appreciated.

Thanks.

***********EDIT*******SOLVED**************

So it turns out after months of stressing about this there was no real knock after all. Matt from Kido Tuning fixed it in about 5 minutes. The false knock was actually wastegate chatter setting off the knock sensor. Here's Matt's explanation:

"It was a combination of the intake AVCS causing lean spool, which generates a lot of exhaust heat(shown in the front O2 sensor resistance) in an attempt to get the engine spooled faster(yet mine spooled faster without it ) and that heat was pushing on the wastegate flap and making it chatter against the turbo."

"WG chatter is the cause, hence why it only occurred at one point and why fuel or timing would not affect it When I pulled timing, it made it worse as it made more heat(more unburnt fuel in exhaust) and in the same breath, more fuel made it worse as it was again, more fuel in the exhaust. So can be diagnosed as a weak WG actuator which is why the mechanics could not hear the knock"

I hope that helps anyone else who has this mystery knock.

[Dropz]

Replace the sensor, replace the fuel filter, run bp98 fuel and you'll be fine.

Knock sensors are notorious in subarus, so if it knocks replace the sensor and run 98.

[Sheik Jabooti]

Thanks for the help.

I always have run bp98 so that's 1 of 3.

I guess I'll change the filter and knock sensor and see if that helps.

Cheers.

[Dropz]

If you already run 98 just do the sensor. I only said filter cos 91 fuel is shit.

[bigBADbenny]

A member here had the same or similar issue and mitigated it using a rubber washer under the knock sensor.

[bass_straitener]

A member here had the same or similar issue and mitigated it using a rubber washer under the knock sensor.

Not sure if that defeats the purpose of the knock sensor. My understanding would dictate it's placement and contact area would have to be as per the factory setup.

Hmm... Not sure if that's a legitimate fix.

[bigBADbenny]

pardon my propagating possible misinformation!

delete posts?

I'm sure I can post some thing a little more constructive...

[Sheik Jabooti]

A member here had the same or similar issue and mitigated it using a rubber washer under the knock sensor.

Funny link. I kinda agree with Bass_Straightner though...not an ideal fix but great bush mechanics and a good point of last resort.

I wonder if changing his knock sensor would have fixed the issue? I guess we'll never know

[PinkK]

Any luck yet? In one of my previous cars I had a dead tensioner pulley (a few of the ball bearings where missing ) which caused my motor to knock, don't know if it would be that but might be something worth checking out?

[Sheik Jabooti]

Any luck yet? In one of my previous cars I had a dead tensioner pulley (a few of the ball bearings where missing ) which caused my motor to knock, don't know if it would be that but might be something worth checking out?

No outcome yet. I will book it into ASG once I drive off the octane booster in the tank. Probably in a week I guess.

Note that the octane booster made no difference to the knock. In fact it's looking more prolific if anything.

[Sheik Jabooti]

To anyone interested I edited the OP with the answer. Thanks to Matt from Kido Tuning.

[CarDoc]

viewtopic.php?f=56&t=17726&start=30

[bigBADbenny]

Don't forget to link every related post everywhere back to that single point.
It's a facinating read. So you are replacing or upgrading the stock wastegate actuator, then retune?

[Sheik Jabooti]

Don't forget to link every related post everywhere back to that single point.
It's a facinating read. So you are replacing or upgrading the stock wastegate actuator, then retune?

Yeah, sorry about the confusion...I've got a few threads all kinda related to this same issue.

Didn't need to change the WG Actuator in the end as Matt was able to tune it out. I might eventually but no need to at the moment as the fine tuning seems to have worked nicely.

[bigBADbenny]

Intriguing! Reading the various threads I had thought the knock issue was due to a mechanical issue.