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Old 09-23-2009, 02:55 PM   #1
windozer
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Default Knock at idle?

Hello all,

I've been noticing that sitting at idle, knock sensor 1 records a decent amount of knock. I would estimate one knock every 10-15 seconds. So a couple questions. Which side of the motor is knock sensor 1 on? From the research I've done it seems like passenger side. The big question is what is causing this, and how should I fix it?

I've heard mention here and there that the suby boxer is noisy, and that sometimes the knock sensors read false knock, but I'd really rather not blow my engine apart. Also, my UEGO reads good AFRs at idle, with a tendancy to swing rich rather than lean. I've cleaned the MAF and reset ECU as well, still shows up.

USDM 04 WRX Wagon - 67k miles - XPT Stage 2 w/catless TBE
Suggestions?
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Old 09-23-2009, 05:14 PM   #2
TurboSetch
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Knock learning is not applicable at idle with stock tables on that car.

Log your IAM or DAM as long as its staying around 16 your car is happy in terms of knock. Use learningview.exe to look at the learned timing adjustments and IAM.

I can't comment on your fueling without more data but the knock at idle is most likely not really knock and even if it is its harmless under no load. It could also be purely a mechanical problem, loose knock sensor, loost brackets on motor, power steering pump, failing internals, bearings, etc.


Bottom line is that if your car is not pulling timing much or at all this is not actually a problem.
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Old 09-23-2009, 05:52 PM   #3
jaxscuby
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knock sensor on driver side..under tmic..
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Old 09-23-2009, 09:20 PM   #4
windozer
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Default Re: Knock at idle?

Thanks. What info should I gather for running rich at idle? I'll check and make sure nothing is rattling around there. My IAM stays at 16 and it doesn't pull timing so like you said probably not a problem. My LV only has one cell with a correction value. I would post but I'm on my iPhone now
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Old 09-23-2009, 11:13 PM   #5
wrxsti.l
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Quote:
Originally Posted by TurboSetch View Post
Knock learning is not applicable at idle with stock tables on that car.
It depends what load is while idling. If the load is above the minimal knock correction thresholds, then knock correction will come into effect.

From my own experiences, knock being "detected" at idle is generally from one of two things:
  1. Noise - intercooler piping, uppipe, dumppipe, catch-can (or anything else metallic) touching/bumping/hitting against something else metallic.
  2. Low timing* - as you lower timing you increase EGT, as EGT increase, combustion temps increase, and that can cause pre ignition. Also at idle you have very low VE and slow combustion speed, and the lower the VE and combustion speed, the higher your advance timing should be.
* Don't just go increasing timing stupidly or you can and will damage your engine.



The following suggestions are for low load and low rpm knock that doesn't seem to go away when lowering timing

My advice is to open a stock ROM and compare the base and advance timing tables to your current ROM's tables. Specifically, compare the values at and around the RPM where the ECU is registering knock when you are idling (around <0.3 load and <1200 rpm).

Then set your current ROM's values to whatever the stock ROMs values are in those cells and smothen the transitioning cells - flash the edited ROM and see if the ECU is still detecting knock (also check the transition load/rpm points while logging to ensure the changes haven't induce new knock.

Saying all that, if setting knock back to stock values at those low load and rpm points doesn't fix it, then it is most likely noise - so check and tighten everything in the engine bay.


Leslie



P.S. I want to reiterate that ppl shouldn't just start increasing their timing, as doing so without carefully logging and evaluating the changes can cause knock and kill your engine quick.
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Old 09-24-2009, 07:42 AM   #6
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wrxsti.l

Thanks, this is good info. I will check out the ROMS as you suggested. Do you have any idea of the rich AFR at idle? The one thing I can think to check is the coolant temp. compensation. Any other ideas?
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Old 09-24-2009, 08:54 AM   #7
wrxsti.l
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What do you mean by rich AFR at idle?

After you initially start the car it will run a little rich until the enrichment comp is over, but then it should go to normal CL target (around 14.6 or whatever).

So once you start the car, if it doesn't start targeting your CL AFR target in around 10seconds (assuming your engine is already warmed up), then something else is wrong.

Do you still have stock injectors and airfilter box/MAF?

Leslie
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Old 09-24-2009, 09:24 AM   #8
windozer
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Quote:
Originally Posted by wrxsti.l View Post
What do you mean by rich AFR at idle?

After you initially start the car it will run a little rich until the enrichment comp is over, but then it should go to normal CL target (around 14.6 or whatever).

So once you start the car, if it doesn't start targeting your CL AFR target in around 10seconds (assuming your engine is already warmed up), then something else is wrong.

Do you still have stock injectors and airfilter box/MAF?

Leslie
After the car reaches normal operating temp, the AFR stays around 13.8-14.0. I still have stock airbox with k&n, stock MAF, and stock injectors. I have logs available, just no good way to post them.

I was looking at my map, I am hitting the coolant compensation table, but it should only be removing .022 AFR. The load compensation would also add .303 off of the 14.57 base target. The math doesn't add up to 13.8
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Old 09-24-2009, 09:30 AM   #9
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Check that the stage ROM you flashed hasn't had the injector latencies or MAF scaling tables changed. If they are changed, then change those tables back to stock settings and test again.
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Old 09-24-2009, 09:34 AM   #10
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Quote:
Originally Posted by wrxsti.l View Post
Check that the stage ROM you flashed hasn't had the injector latencies or MAF scaling tables changed. If they are changed, then change those tables back to stock settings and test again.

No changes. Also to your other question the base timing tables at idle the same.
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Old 09-24-2009, 12:45 PM   #11
bren wrx
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try cleaning or swapping out your maf, ive seen them do this.
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Old 09-24-2009, 01:26 PM   #12
windozer
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Quote:
Originally Posted by bren wrx View Post
try cleaning or swapping out your maf, ive seen them do this.
Tried that already too.
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Old 09-24-2009, 08:41 PM   #13
wrxsti.l
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I might have missed it, but what fuel are you running?
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Old 09-24-2009, 09:00 PM   #14
john 1badSTI
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are your short term trims jumping around alot once warmed up if they are your front fueling o2 sensor is probably on its way out.if you have a lot of miles on the sensor it is probably bad because of the poor clock position in the front manifold they are susceptible to moisture from condensation in the exhaust and that can be worsened by the climate you live in. just my 2 cents, good luck
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Old 09-24-2009, 09:15 PM   #15
windozer
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Default Re: Knock at idle?

I'm running 93 sunoco. I'll check the trims, but if what you said is true, wouldn't the o2 readings be off as well?
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Old 09-29-2009, 01:41 AM   #16
Rextion
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This is really odd!
I am also getting knock at idle. (from knock sensor # 1 as well)

I just replaced my catted uppipe with a turboxs cattless and now I am throwing a P0304 and getting knock at idle
WTF
Someone suggested changing my plugs... but I didn't know if that would be the cause.
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