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Hi Guys,

My tuner and I have encountered an issue where my car is knocking even though the tune is beautiful. I used Shell 91 octane gas and it still knocks at low RPM when I'm applying throttle on the freeway!

The car doesn't knock at high speeds (which makes since because the ignition timing falls into sync it seems.

My tuner has been tuning cars for roughly 25 years and said he is clueless what it could be, but I think he may have glossed over my current spark plugs, which are still stock. Could this be the case?

I did some reading and I am curious if any of you have encountered a similar problem on your Stock K24 turbo'd?

-Do I need Iridium Spark Plugs now?
-Do I need to mix 100 octane gas with my 91 octane gas all the time (expensive)?

Thanks for any help in advance!
 

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...but I think he may have glossed over my current spark plugs, which are still stock....
So what you're saying is, you haven't even pulled & looked at them yet?

I'd try that first. Spark plugs often tell the story of what's going on in there - too rich, too lean, etc, etc.

Doesn't make sense that it would only happen at low RPM and not high...not unless it just gets muffled with the louder engine noise and you can't hear it.

Timing slipped a little, maybe?

Just tossing ideas.
 

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So what you're saying is, you haven't even pulled & looked at them yet?

I'd try that first. Spark plugs often tell the story of what's going on in there - too rich, too lean, etc, etc.

Doesn't make sense that it would only happen at low RPM and not high...not unless it just gets muffled with the louder engine noise and you can't hear it.

Timing slipped a little, maybe?

Just tossing ideas.
Yeah my tuner did suggest noise, but this was because it was only knocking a few random times on the dyno at 60-80mph speeds. Then when I got on the highway and pushed the throttle, the knocking was worse than on the dyno.

I will have a look at the spark plugs. I hope these are the source.
 

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1st things 1st.. Can you do some datalogs and post them on here when you knock? Look at the knock level vs knock threshold.... Does it knock around vtec? What rpms?
 

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Well I got aj oil change yesterday and installed NGK iridium spark plugs. I am using a mixture of 91 and 100 octane gas.

Thing is, we the knocking only started happening AFTER we got the vtec solenoid to start working, so I'm thinking it could be the crossover frequency that's setting off the knock sensor...

Does this sound right?
 

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when my k24 hits vtec it will register a knock half the time this is normal but post a datalog for us to look at to c for sure include ur vtec engagement rpm and you motor setup
 

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lol first thing i would be checking is the oil... any sign of shavings?
Well I got aj oil change yesterday and installed NGK iridium spark plugs. I am using a mixture of 91 and 100 octane gas.

Thing is, we the knocking only started happening AFTER we got the vtec solenoid to start working, so I'm thinking it could be the crossover frequency that's setting off the knock sensor...

Does this sound right?
Didnt really answer his question......

Anyhow, Not sure about how many people run the knock sensor with a boosted setup.. I know I dont.
 

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Didnt see it mentioned, figured I'd throw it out there in case you didn't know....may or may not help..

I know some guys running FI setups are saying to run with 1 size/range colder plugs - and that seems to help some of the issues they were having.
 

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how do u know if ur knocking without a knock sensor whats ur reason for not running one
If you can hear it from the interior, I'd have a reason to be worried too.

This is, however, the first time I'm aware of some people not running a knock sensor, though. I too would like to know why.
 

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i was taught if you hear the knock from the interior its probably too late damage already done i tune my high boost setup with the factory knock sensor works great
 

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If you can hear it from the interior, I'd have a reason to be worried too.

This is, however, the first time I'm aware of some people not running a knock sensor, though. I too would like to know why.
The factory knock sensor is so sensitive that it has a tendency to register knock even when it's not there. That's the reasoning I have heard, however I still utilize my stock sensor and have the K-Pro set up to flash the MIL if it detects knock. On E85 though, I have never seen any knock. I would suspect that the 91 octane just doesn't have the detonation resistance that you need, although it's really up to the tune. I would recommend, as stated before, to check the plugs and step them down one range colder. I'd stick with the less expensive copper plugs since, even though they wear out quicker, they aren't as easy to blow out as iridiums. OP, have you considered running E85?
 

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The factory knock sensor is so sensitive that it has a tendency to register knock even when it's not there. That's the reasoning I have heard, however I still utilize my stock sensor and have the K-Pro set up to flash the MIL if it detects knock. On E85 though, I have never seen any knock. I would suspect that the 91 octane just doesn't have the detonation resistance that you need, although it's really up to the tune. I would recommend, as stated before, to check the plugs and step them down one range colder. I'd stick with the less expensive copper plugs since, even though they wear out quicker, they aren't as easy to blow out as iridiums. OP, have you considered running E85?
I have heard this as well about the factory sensor being too sensitive. If your car is seriously gutted it will pick up occasional knocks from all the rattles/stiffness have had this happen in a couple friends cars saw it first hand.

You're tuner has been tuning for 25 years what does he think of re-checking it with an oscilloscope to see if it's actually picking up anything worst case. After checking the plugs first of course.
 

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Didnt see it mentioned, figured I'd throw it out there in case you didn't know....may or may not help..

I know some guys running FI setups are saying to run with 1 size/range colder plugs - and that seems to help some of the issues they were having.
what number plus for and k24a colder
 
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