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Old 06-29-2020, 05:04 PM   #1
Jp925
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Default Single cylinder misfire p0302

Iíve searched on YouTube and read numerous posts on here, hoping someone can shed some light on this or at least explain the inner workings of this code

Car is an 06 STi, Spt intake, bone stock. 123000 miles original motor. I have an accessport v3 but itís not installed to be tuned.

Car gets around 200 miles to a tank, and eats about half quart of oil every other fill up.

A few weeks ago the car started shaking at idle and then started throwing a single cylinder misfire, p0302 misfire in cylinder 2. Accessport confirms the misfire and itís indeed isolated to just number 2.

Spark plugs are 1000 miles old
Iíve swapped coil pack, plug, and injector all with cylinder 4, no change in behavior.

Hereís where it gets weird, car will ONLY misfire at idle, If Iím above 1200rpm and actually driving, car runs flawless; accessport confirms 0 misfires.

Where should I go from here test wise? Has anyone seen idle misfires isolated to a single cylinder before?

Thanks for the help!
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Old 06-29-2020, 05:16 PM   #2
Samurai Jack
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Originally Posted by Jp925 View Post
Iíve swapped coil pack, plug, and injector all with cylinder 4, no change in behavior.
Did you change all at the same time or one at a time? Makes a big difference.
Did you check for vacuum leaks?

Did you look up P0302 and see the list of all the potential issues? Always easy ones first.

Did you know that just because it says P0302 does not mean it could not be any one of the other 3 cylinders?

CELS are approximate, never exact.
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Old 06-29-2020, 05:22 PM   #3
Jp925
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Originally Posted by Samurai Jack View Post
Did you change all at the same time or one at a time? Makes a big difference.
Did you check for vacuum leaks?

Did you look up P0302 and see the list of all the potential issues? Always easy ones first.

Did you know that just because it says P0302 does not mean it could not be any one of the other 3 cylinders?

CELS are approximate, never exact.
I changed one at a time and would check with the accessport the cylinder roughness count on all cylinders, number 2 is the only one with a count.

I have not checked for vacuum leaks, but I have replaced a lot of lines in the last 6 months. How would a vacuum line cause roughness in a single cylinder?
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Old 06-30-2020, 01:19 AM   #4
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Compression/leak down test. You may have a broken ringland causing the misfire; better to check before it lets go
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Old 06-30-2020, 03:41 AM   #5
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Compression/leak down test. You may have a broken ringland causing the misfire; better to check before it lets go
Wouldnít it get worse under load if a ringland was going out?
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Old 06-30-2020, 08:57 AM   #6
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I have not checked for vacuum leaks, but I have replaced a lot of lines in the last 6 months. How would a vacuum line cause roughness in a single cylinder?
As I mentioned earlier, CELs point you in a specific direction but CELs do not necessarily point you to the exact specific issue. They are only guides. It is not an exact science.

A vacuum leak could be the culprit.
Focus a little less on just cylinder #2 and more on what could be causing the CEL.

Quote:
Originally Posted by bp05obxt
ompression/leak down test. You may have a broken ringland causing the misfire; better to check before it lets go
I think you are jumping to conclusions. Because the 2.5 has a history of ringland issues, many people immediately jump to ringland failure as a cause for everything.
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Old 06-30-2020, 11:02 AM   #7
Jp925
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Originally Posted by Samurai Jack View Post
As I mentioned earlier, CELs point you in a specific direction but CELs do not necessarily point you to the exact specific issue. They are only guides. It is not an exact science.

A vacuum leak could be the culprit.
Focus a little less on just cylinder #2 and more on what could be causing the CEL.


I think you are jumping to conclusions. Because the 2.5 has a history of ringland issues, many people immediately jump to ringland failure as a cause for everything.
Maybe Iím a bit confused, if the car is throwing a specific code isolated to a single cylinder, and the accessport gauge data confirms 0 roughness on 1,3, and 4; youíre saying I should be looking else wear?
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Old 06-30-2020, 11:20 AM   #8
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I'm saying that just because the CEL reads P0302 does not always mean the issue is specifically cylinder #2. CELs are not an exact science.

P0302 is what the scanner is telling you where it believes the issue lies based on a series of inputs it receives from the ECU.

What you are experiencing as a rough idle could be linked to a vacuum leak and not be directly related to cylinder #2 itself. Cylinder #2 may be perfectly OK.

You said yourself you swapped coil pack, plug, and injector all on cylinder 2 one at a time with cylinder #4 and you saw no change. These are the most common parts to start with.

I've seen this before and it has turned out to be some type of vacuum leak.
Now, it may not be, but I'm saying don't rush to the conclusion that the cylinder is bad when this only happens at idle.
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Old 06-30-2020, 12:41 PM   #9
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i would listen to bp05obxt, if you already tried swapping coil packs and plugs and its still isolated that cylinder, thats a good indicator, also your saying a half quart of oil between every other fill up so roughly every 4-500 miles would indicated to me either a possible ring/ringland issue. compression and leak down would be the steps id take next in diagnosing
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Old 06-30-2020, 03:57 PM   #10
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Originally Posted by Aristocrat Autosport View Post
i would listen to bp05obxt, if you already tried swapping coil packs and plugs and its still isolated that cylinder, thats a good indicator, also your saying a half quart of oil between every other fill up so roughly every 4-500 miles would indicated to me either a possible ring/ringland issue. compression and leak down would be the steps id take next in diagnosing
Gonna dive into the fun stuff tomorrow, thanks for the input.
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Old 06-30-2020, 10:09 PM   #11
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I'm saying that just because the CEL reads P0302 does not always mean the issue is specifically cylinder #2. CELs are not an exact science.

P0302 is what the scanner is telling you where it believes the issue lies based on a series of inputs it receives from the ECU.

What you are experiencing as a rough idle could be linked to a vacuum leak and not be directly related to cylinder #2 itself. Cylinder #2 may be perfectly OK.

You said yourself you swapped coil pack, plug, and injector all on cylinder 2 one at a time with cylinder #4 and you saw no change. These are the most common parts to start with.

I've seen this before and it has turned out to be some type of vacuum leak.
Now, it may not be, but I'm saying don't rush to the conclusion that the cylinder is bad when this only happens at idle.
These cars have fairly advanced ecuís why would it throw a misfire code isolated to a single cylinder, as well as count misfires in real time data logging if something else is wrong? The ecu monitors hundreds of things that can throw codes monitoring the slightly off reading; Why do you think i should be looking else where?
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Old 07-01-2020, 02:04 AM   #12
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do a compression test on #2 and 4 to see what they are. if they are within 15% of eachother at least you know its not a compression problem. when was the last time you changed your coils? Also just inspect the coils for discolorations on the plastic or the rubber boots.
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Old 07-01-2020, 03:44 AM   #13
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do a compression test on #2 and 4 to see what they are. if they are within 15% of eachother at least you know its not a compression problem. when was the last time you changed your coils? Also just inspect the coils for discolorations on the plastic or the rubber boots.
Coils are original from 06, 123k miles. They look and seem fine, and switching them around didnít bring the problem to another cylinder.
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Old 07-01-2020, 09:03 AM   #14
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Originally Posted by Jp925 View Post
These cars have fairly advanced ecuís why would it throw a misfire code isolated to a single cylinder, as well as count misfires in real time data logging if something else is wrong? The ecu monitors hundreds of things that can throw codes monitoring the slightly off reading; Why do you think i should be looking else where?
You don't seem to understand how CELs work. The code points to a general area of where the problem may lie, but they don't give an exact answer.

Google P0302 and there is a long list of potential problems which include the things you have already tried as well as many other possibilities which would result in a P0302. It could just as easily given you any one of the other 3 cylinders.

I've fixed that issue in the past. Vacuum leaks, bad gas, dirty IACV ( which I don't think came on the 06 model & up ).

Quote:
Originally Posted by Jp925
Coils are original from 06, 123k miles. They look and seem fine, and switching them around didnít bring the problem to another cylinder.
You can't tell if igniters are good or bad just by looking at them. At 123k, may be an issue, maybe not. One may be starting to fail, resulting in an issue.
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Old 07-02-2020, 05:05 PM   #15
603boostfreeordie
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Default Single cylinder misfire p0302

Quote:
Originally Posted by Aristocrat Autosport View Post
i would listen to bp05obxt, if you already tried swapping coil packs and plugs and its still isolated that cylinder, thats a good indicator, also your saying a half quart of oil between every other fill up so roughly every 4-500 miles would indicated to me either a possible ring/ringland issue. compression and leak down would be the steps id take next in diagnosing


Agreed I was waiting for someone to question the oil. Thatís a fair amount some tests could save you from a big bill. I have a 2012 wrx 124k running 18 Lbs and consume almost no oil between oil changes.
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Old 07-03-2020, 02:54 AM   #16
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Agreed I was waiting for someone to question the oil. Thatís a fair amount some tests could save you from a big bill. I have a 2012 wrx 124k running 18 Lbs and consume almost no oil between oil changes.
Do you mean like sending a sample off to analysis?
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Old 07-03-2020, 08:48 AM   #17
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Originally Posted by Jp925 View Post
Do you mean like sending a sample off to analysis?


No I mean like compression and leakdown. Itís a cheap couple tests and if you take it to a Subaru performance shop they will probly get it fixed quick and possibly save the motor. Do you do your own oil changes have you found any reasons for loosing so much oil?
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Old 07-03-2020, 04:49 PM   #18
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No I mean like compression and leakdown. Itís a cheap couple tests and if you take it to a Subaru performance shop they will probly get it fixed quick and possibly save the motor. Do you do your own oil changes have you found any reasons for loosing so much oil?
Iím going to leak test down test. The car was purchased used from a guy who had a blown turbo. Iíve only had the car for about 2500 miles.
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Old Yesterday, 05:07 PM   #19
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any results from the leakdown/compression test?
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