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Cyl 2 misfire at idle


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So my car has developed a misfire in cyl 2. Logging it shows it only happens at idle, never under load. It's minor when the car is warmed up, but misfires all over the place when cold.

 

Spark plugs are less than a year old. No other problems. Any ideas?

 

I just ordered a new spark plug, and I just put in a bottle of injector cleaner yesterday.

Edit- I found the solution (bumped here to make searching easier). It was a bad injector. Swapped two injectors and the problem moved, so I replaced the faulty one and the problem is resolved!

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My guess is that its either spark plug/coilpack related, or injector related. We'll see if the injector cleaner helps while my spark plug is on its way. If the spark plug doesn't fix it, I'll swap coil packs. If that doesn't help, ill swap injectors to see if the problem moves.

 

But any other insight would be great!

 

P.s. Doc, still waiting for logs!

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Also do a compression test to rule out bad valves. Since you don't appear to have any noises I think it's safe to rule out ring land failures.

 

Since it only does the misfire at idle (and mainly when cold), wouldn't that rule out a problem with the valves?

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Just had my 3.0R in for code P0304.. cylinder 4 misfire. Tech sprayed coils there was no arch, cleared the code and test drove OK. I can still feel it misfiring when first started up and occasionally at a red light. Read other threads that reported knock sensor was causing the same issue but never diagnosed by Subaru Techs.
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Glad that so many people are interested in my problem! I'll be sure to post up all the info I can.

 

Well I have a slight stumble at idle, never got a misfire code, but I've checked a number of things including compression and plugs (both looked excellent).

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Here's a log of my misfires. Car has been parked for about 4hrs, so it's cold. So far it looks like the injector cleaner hasn't helped. Added to tank at about 3/4 full, and now at about 1/4 full. I used Lucas, since I find that they are one of the best.

 

Also, there's currently no CEL on right now. Has been off ever since I reset it a few days ago. That tells me the car isn't doing it/noticing it often enough to log it (i.e. only when cold).

romraiderlog_20100619_211906.csv

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Since it only does the misfire at idle (and mainly when cold), wouldn't that rule out a problem with the valves?

 

A bad valve would be most prominent at idle since it would have a devastating impact on compression.

 

Here's a log of my misfires. Car has been parked for about 4hrs, so it's cold. So far it looks like the injector cleaner hasn't helped. Added to tank at about 3/4 full, and now at about 1/4 full. I used Lucas, since I find that they are one of the best.

 

And injector cleaner only works to a certain extent. But it can be an electrical malfunction in the injector or that it's sticky and don't open or close in time.

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A bad valve would be most prominent at idle since it would have a devastating impact on compression.

 

 

 

And injector cleaner only works to a certain extent. But it can be an electrical malfunction in the injector or that it's sticky and don't open or close in time.

 

But a bad valve would also register problems all across the powerband, wouldn't it? I'm not having much trouble hitting 16psi, which is what i'm tuned for. And overall it feels pretty smooth. No misfires logged while driving.

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Not necessarily. See it as a water tap that doesn't close properly but is always going from a slow flow to a full flow. At higher RPM:s the slow flow doesn't matter much but at lower it will consume all compression.
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So my car has developed a misfire in cyl 2. Logging it shows it only happens at idle, never under load. It's minor when the car is warmed up, but misfires all over the place when cold.

 

Spark plugs are less than a year old. No other problems. Any ideas?

 

I just ordered a new spark plug, and I just put in a bottle of injector cleaner yesterday.

 

mine came out to be bad injectors+fuel pump. If you dont mind, replace all of them (4 injectors).

 

Also, if your car idles rough, check your battery and alternator, have them test at the local auto part store. (symptoms: loud bearing belt noise, burning smell)

 

Good luck, :)

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And make sure that they are matched even though the injectors seems to be good individually they may be giving different flow, which also can cause problems and prematurely age the cat.

 

yep, that's why I recommended to replace all 4 (make sure get new O-rings too).

 

and +1 they have to be matched brand and type.

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yep, that's why I recommended to replace all 4 (make sure get new O-rings too).

 

and +1 they have to be matched brand and type.

 

Well let's hope I don't have to replace injectors. My spark plug should arrive this week, and if it comes by Thursday then that's when i'll install it. That's step 2. After that, it's swapping injectors to see if the problem moves.

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Well let's hope I don't have to replace injectors. My spark plug should arrive this week, and if it comes by Thursday then that's when i'll install it. That's step 2. After that, it's swapping injectors to see if the problem moves.

 

did you check your alternator and battery by any chance?

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Just use a volt meter to check the battery voltage. If there is a shorted cell you may get some strange errors even though things seems to be alright anyway. It's a quick job.

 

Voltage should be something around 12V when ignition is off and with engine running 13.6 to 14.4 volts. (Not much above 14.4 since if it goes higher the battery will start to boil.)

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Just use a volt meter to check the battery voltage. If there is a shorted cell you may get some strange errors even though things seems to be alright anyway. It's a quick job.

 

Voltage should be something around 12V when ignition is off and with engine running 13.6 to 14.4 volts. (Not much above 14.4 since if it goes higher the battery will start to boil.)

 

I'll see if I can borrow one...I don't have a volt meter (it's on my wish list).

 

Update- I replaced the spark plug a few days ago. No change in the hesitation. It still does it when the car is fully cold, but not when it's warmed up.

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I'll see if I can borrow one...I don't have a volt meter (it's on my wish list).

 

Update- I replaced the spark plug a few days ago. No change in the hesitation. It still does it when the car is fully cold, but not when it's warmed up.

 

a weak battery could kill the alternator, and a failed alternator could bring down the whole car (rough idle). Look like you have issue with the injectors but checking the charging system will worth a try :)

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I'll see if I can borrow one...I don't have a volt meter (it's on my wish list).

 

Update- I replaced the spark plug a few days ago. No change in the hesitation. It still does it when the car is fully cold, but not when it's warmed up.

 

That seems to indicate a lean setup, which leads me to suspect that an injector or O2 sensor is the problem. But swap around the coil packs first and see if the problem moves. It may be a temperature related problem.

 

You can probably find a cheap multimeter at Autozone for $10 or $20... Sufficient for car use. Just don't mix up measuring amp and volt! :p

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