Knock sensor Negative and positive reading

[Sean4m]

Hi I have a 2015 mustang gt, only mods I have are a cai and a borla exhaust. Recently had my ac compressor changed and my knock sensor started reading anywhere from -1 too -9 degree depending on the rpm and gear I was in. I will point out my knock sensor always read 0.00 prior too changing my compressor. The other day I noticed in first gear I was getting positive knock. Anywhere from 0.00-2.97 at the highest. I messaged my tuner but haven’t heard from him yet. The positive knock is very random and from a log I looked at only happens from 950 -1100 rpm and goes straight back to zero degrees. Ive read a lot of forums and can’t find anything on reading both negative and positive degrees of knock. Hear a few people say it could be from a exhaust rattle going too check it tomorrow. Just looking for some insight on why my knock sensor is randomly reading both negative and positive knock.

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[kluke15]

neg knock is good = added timing. positive knock is bad. but being intermittent id bet something is making contact under certain conditions and rattling causing false knock.

 

[Sean4m]

neg knock is good = added timing. positive knock is bad. but being intermittent id bet something is making contact under certain conditions and rattling causing false knock.

Okay thank you will look around for anything loose

 

[Vert]

Are you still on the gas in 950-1100 range? I know mine hits + when I get off the gas. If you're not getting +knock when going WOT, not much to worry about.
I wonder if you was getting negative knock, but your old compressor was adding knock due to noise/vibration which cancelled out the neg knock and caused to knock to end up at 0.

 

[Sean4m]

Are you still on the gas in 950-1100 range? I know mine hits + when I get off the gas. If you're not getting +knock when going WOT, not much to worry about.
I wonder if you was getting negative knock, but your old compressor was adding knock due to noise/vibration which cancelled out the neg knock and caused to knock to end up at 0.

Yes am still getting positive knock in that specific rpm range. The old compressor was really worn out, the compressor clutch went on it. I checked the bolts on the compressor and the serp belt tensioners, I didn’t see anything thats wobbly, exhaust seemed okay as well. My ac compressor doesn’t have the ac belt on it currently am waiting for it too come in but I doubt that would cause any issues other then no ac. If the tuner doesnt find anything unusual on the logs I’ll be completely out of ideas.

 

[Sean4m]

Is there any chance that the tune on my car is causing the positive knock at that specific rpm?

 

[kluke15]

put some octane booster and see if that helps the knock. if you still get knock with the booster then its probably false knock and something somewhere is making noise. if knock is gone with booster then it may be real.

 

[Sean4m]

Hey guys update tried everything even got my entire exhaust welded instead of clamps couldn’t find the issue. I switched from the tuner my car came with and went too auto mafia tuning out of Florida and once I loaded their base map completely fixed the positive knock. So far everything’s been great.

 

[gadgtfreek]

Hey guys update tried everything even got my entire exhaust welded instead of clamps couldn’t find the issue. I switched from the tuner my car came with and went too auto mafia tuning out of Florida and once I loaded their base map completely fixed the positive knock. So far everything’s been great.

Good to hear. When I first loaded the Lund tune, with CAI and exhaust, I watched knock for a few months. Was always 0 to -4.5 I think under load (93 octane), so I've stopped watching since. Full Boogie!

 

[Sean4m]

Good to hear. When I first loaded the Lund tune, with CAI and exhaust, I watched knock for a few months. Was always 0 to -4.5 I think under load (93 octane), so I've stopped watching since. Full Boogie!

Mines right around the same 0 to -6

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