False knock at 2000 rpm?

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False knock at 2000 rpm?

Postby Sheik Jabooti » Thu Jul 19, 2012 1:35 pm

Does anyone have any experience in false knock around 2000 rpm?

I have been through a very long winded tuning process with Xtreme Race Tuning and we can't get rid of the knock at 2000 rpm. Finally took it to a tuning mechanic (ASG in Perth) and he had a listen and said that it is normal 2.5T engine noise. Unfortunately that normal noise causes the car to retard at those rpm leaving me with a flat spot. :(

So the question is do I replace the knock sensor because it may be overly sensitive or tune out the knock correction at these low rpm? Chances are that replacing the knock sensor will be a $300-400 pointless exercise. This has been the case in a few forums I've read (eg. http://www.romraider.com/forum/viewtopi ... =15&t=6294).

Any opinion with this would be greatly appreciated.
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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Re: False knock at 2000 rpm?

Postby Sheik Jabooti » Sun Jul 22, 2012 3:44 pm

Just to add to this story, I added a bottle of octane booster to 3/4 tank of 98 ROM fuel (this should give me >100 RON) and still got the same knocking at lower rpm. In fact it almost seems to be knocking more at other rpm's? :shock: That doesn't seem right. Or is it possibly the signs of a faulty (overly sensitive) knock sensor?!?
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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Re: False knock at 2000 rpm?

Postby Sonic » Tue Jul 24, 2012 7:51 am

If all is well mechanically no leaks and such,just adjust the rpm and load ranges that activates FLKC and FBKC to a higher range like enable at 2300rpm and disable 2200rpm and load range enable above 1.2 and disable 1.1.These are just examples dont set them to high cause you wont have the necessary protection.
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Re: False knock at 2000 rpm?

Postby Dropz » Tue Jul 24, 2012 7:55 am

If more octane makes it knock more, have you considered trying 95 or 91 octane to compare? Have you checked your spark plug gaps?
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Re: False knock at 2000 rpm?

Postby Sheik Jabooti » Tue Jul 24, 2012 12:26 pm

Spark plugs just got checked a few weeks ago...they were in near new condition according to the mechanic, no wear and perfectly gapped. He also went around looking for anything loose that would cause false knock. The fact that the knock count goes up in idle suggests that its not something loose I guess.

Not sure about putting in 91/95 RON as that's just making the fuel worse. The cars only rated for 95+ anyway.
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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Re: False knock at 2000 rpm?

Postby Dropz » Tue Jul 24, 2012 1:38 pm

I only suggest it to cancel out a fuel issue. You have said that it happens with 98ron and 98ron plus octane booster, so I suggest at least trying the opposite to see if it has the same/reverse/no effect
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Re: False knock at 2000 rpm?

Postby <GB> » Tue Jul 24, 2012 4:26 pm

could be a little piston rattle....
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Re: False knock at 2000 rpm?

Postby Sheik Jabooti » Tue Jul 24, 2012 5:12 pm

<GB> wrote:could be a little piston rattle....


How would you stop it setting off the knock sensor?
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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Re: False knock at 2000 rpm?

Postby <GB> » Tue Jul 24, 2012 5:44 pm

Sheik Jabooti wrote:
<GB> wrote:could be a little piston rattle....


How would you stop it setting off the knock sensor?

i would be asking your mechanic to listen to it on cold start and see if its evident , it may not have any but i have seen a fair few boxer engines with piston slap. And even if it does have noise it may not be able to cause the knock sensor to pick up on it.
if it did have some and it was causing your issue then im not sure how to fix in the engine managemant side of things from a mechanical point you could try and oil change with some better oil and see if it helps stop the rattle. what weight oil are you using? when was the last time you changed it? how many km has your car done?

oil change is a cheap and needs doing anyway..

there could even be something else thats causing the knock you might want to get someone with an ocilscope to look at it and see if they can pick up what its doing.

see if you can borrow a knock sensor off someone else or buy one second hand to test

what does the tuner say?

could do a compression test and leak down test


there is a number of things that could cause pining, when was the cam belt replaced last?
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Re: False knock at 2000 rpm?

Postby Sheik Jabooti » Tue Jul 24, 2012 6:14 pm

<GB> wrote:i would be asking your mechanic to listen to it on cold start and see if its evident , it may not have any but i have seen a fair few boxer engines with piston slap. And even if it does have noise it may not be able to cause the knock sensor to pick up on it.
if it did have some and it was causing your issue then im not sure how to fix in the engine managemant side of things from a mechanical point you could try and oil change with some better oil and see if it helps stop the rattle. what weight oil are you using? when was the last time you changed it? how many km has your car done?

oil change is a cheap and needs doing anyway..


Car's done just under 40k so not alot really. Driven mostly around the city...occasionally given some stick but not often. Just had it serviced a few weeks ago, oil, 2 cans of head cleaner, fuel cleaner, etc. Mechanic reckons it sounded ok. Also took it to a second mechanic (ASG in Perth) and he listened on startup and reckon it was a typically noisey late model liberty...nothing special, probably drive train/valve noise he said and maybe an overly sensitive knock sensor (I didn't know they had feelings :wink: ).

<GB> wrote:there could even be something else thats causing the knock you might want to get someone with an ocilscope to look at it and see if they can pick up what its doing.

see if you can borrow a knock sensor off someone else or buy one second hand to test


Yep I think I need some more test equipment to better diagnose it. Unfortunately don't have a second hand sensor and new ones are ~$150...but that was one of my next things to try.

<GB> wrote:what does the tuner say?


lols...this if the frustrating bit. Edward from XRT reckons I should sell the car now!...Matt from Kido reckons from the logs, the engine appears fine. So what do you make of that!?! :?

That's why I need to get to the bottom of this, as I don't want to spend mod money on a car that's just about to blow up!


<GB> wrote:could do a compression test and leak down test
there is a number of things that could cause pining, when was the cam belt replaced last?


Compression is probably ok but could be something to test.

Thanks for the thoughtful reply. :)
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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Re: False knock at 2000 rpm?

Postby <GB> » Wed Jul 25, 2012 8:48 am

why does edward say to sell it? is the flat spot that bad?
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Re: False knock at 2000 rpm?

Postby Sheik Jabooti » Wed Jul 25, 2012 12:06 pm

<GB> wrote:why does edward say to sell it? is the flat spot that bad?


Well I guess he considers it something very bad...but he only has logs to go by and he's a tuner not a mechanic. My best bet is to take it to All Star Garage here in Perth as they have a dyno.

Sometimes I just hate cars...such money pits :cry:
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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Re: False knock at 2000 rpm?

Postby Robbks » Wed Jul 25, 2012 1:47 pm

Sheik Jabooti wrote:
<GB> wrote:why does edward say to sell it? is the flat spot that bad?


Well I guess he considers it something very bad...but he only has logs to go by and he's a tuner not a mechanic. My best bet is to take it to All Star Garage here in Perth as they have a dyno.

Sometimes I just hate cars...such money pits :cry:


take it to Doug and the guys at STechnic.
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Re: False knock at 2000 rpm?

Postby <GB> » Wed Jul 25, 2012 2:16 pm

tell me about it im thousands in.. an not much result lol i seen your other thread too ill watch and see what happens
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Re: False knock at 2000 rpm?

Postby Sheik Jabooti » Wed Jul 25, 2012 2:33 pm

Robbks wrote:
Sheik Jabooti wrote:
<GB> wrote:why does edward say to sell it? is the flat spot that bad?


Well I guess he considers it something very bad...but he only has logs to go by and he's a tuner not a mechanic. My best bet is to take it to All Star Garage here in Perth as they have a dyno.

Sometimes I just hate cars...such money pits :cry:


take it to Doug and the guys at STechnic.



Talked to the guys at S-Technic and they suggested ASG as the ASG guys are fully equipped with knock sensing equipment and a dyno.

The STechnic guys are really helpful and knowledgeable though and will probably sort my exhaust mod when ready.
Started with a Gen2 Outback, then got a MY07 GT Spec.B Manual w Cat Back Exhaust and Verso Tuned, now got 2 kids and a MY07 GT Auto Wagon, Ultrex stealth back exhaust, panel filter, Whiteline Sways all round, Spec.b struts and springs and Kido-Tuned.
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