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Old 10-26-2022, 01:01 PM   #1
Scooby Newbie
Member#: 326147
Join Date: Jul 2012
Location: Philly
2004 STI

Default Knock sensor malfunctioning due to oil leak?

I have no check engine lights, however I am now getting a very odd issue.

DAM is dropping from 1 to .5 or even lower, during gear shift at low rpm. Usually between 1/2 or 2/3 gear.

I can physically feel a ďbuckĒ from it pulling timing as the dam drops. Almost like a sputter of bad gas. I did drain out my fuel tank and filled up with 10 gallons of fresh 93 to rule that out.

Tuner said to check for things rattling around engine which I did but donít see anything obvious.

I did notice I have a little oil leak from where the hardline of the crank case hardline goes and the knock sensor is covered in oil.

Now, I know this isnít ideal, and Iím going to be fixing the leak, but would a knock sensor with oil contamination cause it to report false knock potentially leading to this issue?

I reset the ecu and did a 3rd gear pull and no knock is detected during the pull, so and the problem is really brought on during low gear gear shifts.

I ordered a new sensor to rule it out and also ohmed out the old sensor, but it was within spec.

Any ideas?

Forgot to mention I do have a built motor, but this has never been an issue before and was just driving the car last week fine!

So can oil on the knock sensor cause it to read false knock or act weird, despite Ohming out within spec with a multimeter?

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Old 10-30-2022, 11:04 PM   #2
Scooby Specialist
Member#: 419354
Join Date: Apr 2015
Chapter/Region: MAIC
Location: Newark, Delaware
2007 STI
Crystal gray metallic


I doubt it.
Oil up there is coming from the power steering pump, loose AVCS, or turbo feed, (unlikely since DAM has shifted) or the crankcase, which means a faulty PCV system or excessive blowby + hose leak. Excessive pressure in the crankcase usually means rings are toast or a ringland failure.
I'd be surprised if a knock sensor solves the issue, oil being up there indicates a larger problem. Effort & money are better spent getting a test kit off Amazon & pulling plugs to do a compression & leak down test first in my opinion.

Last edited by Subie_; 10-31-2022 at 03:39 AM.
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