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Old 12-02-2019, 10:57 AM   #1
smccloud
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Default Misfire when cold outside

My 2008 Impreza 2.5i has developed a weir misfire issue only when its cold outside (and given that we now have snow on the ground in Minnesota it won't be warm again for a while). It will throw random cylinder 1 & 3 misfire codes until there is some heat in the engine, then it runs fine. I can smell unburnt fuel in the exhaust so I know the injectors are firing. I haven't done much more than make sure the coil pack is fully plugged in and the wires are fully plugged in yet since I haven't had a lot of time. I'd just like some things to look at to start.

Last summer I put head gaskets in it, including a new radiator cap which being aftermarket failed already. But it still ran fine even when cold up until this point. Took it to a local shop since I thought it needed head gaskets again, the put a new cap in it and this is when it started misfiring. This cap also went out (again aftermarket) so I put a brand new Subaru cap on it and that is fine now.

The plan this winter was to have my wife take my car once a week to get some more miles on it, but until I figure this out I don't want to let her take it. I don't want to just start throwing parts at it either. I'm currently running E3 Spark Plugs in it, could these be part of the problem? When I put the head gaskets in it, I missed a couple grounds, do I need to check the ones running to the heads to make sure they are tight?
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Old 12-02-2019, 12:19 PM   #2
viper_crazy
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I don't know if the 2.5i are prone to this, as they have a differently designed intake, but on some WRX's of this era, there's an intake-to-tgv ring seal that weren't made thick enough and contract too much in the cold and basically cause an air leak. Subaru updated the part and p/n with thicker seals that solves this problem. Might be worth looking into if this applies.
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Old 12-02-2019, 01:34 PM   #3
smccloud
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Quote:
Originally Posted by viper_crazy View Post
I don't know if the 2.5i are prone to this, as they have a differently designed intake, but on some WRX's of this era, there's an intake-to-tgv ring seal that weren't made thick enough and contract too much in the cold and basically cause an air leak. Subaru updated the part and p/n with thicker seals that solves this problem. Might be worth looking into if this applies.
I don't think my 2.5i has TGVs at all. Its like it isn't firing those two cylinders. Doesn't look to fun to get at the spark plugs with the engine in the car either

Additionally, I do remember getting a cam position sensor code and cam phaser (not sure if that is the correct name in Subaru lingo but I'll go with what I know) once. However, they have never come back and the misfire ones do. Although according to https://subaruparts.com my car doesn't have variable valve timing but I could have sworn I saw it when I had it apart.

Last edited by smccloud; 12-02-2019 at 01:40 PM.
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Old 12-02-2019, 02:06 PM   #4
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Reading more online, its looking like I will want to pull those plugs and inspect them. Also possible my cheap (yeah right) O'Reily wires are part of the problem too.
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Old 12-02-2019, 02:18 PM   #5
yarrgh
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These cars tend to run well on NGK spark plugs. Those E3 plugs just look like a marketing gimmick. The spark is only going to go to one of the 3 electrodes, the other 2 are simply in the way of flame propagation. I can't guarantee that these are the cause, but they could certainly contribute.

Your misfires are on cyls 1/3, which share a cam. You also mention a cam code. Might want to double check the timing.

It never hurts to check grounds for a clean connection.
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Old 12-02-2019, 02:21 PM   #6
smccloud
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Quote:
Originally Posted by yarrgh View Post
These cars tend to run well on NGK spark plugs. Those E3 plugs just look like a marketing gimmick. The spark is only going to go to one of the 3 electrodes, the other 2 are simply in the way of flame propagation. I can't guarantee that these are the cause, but they could certainly contribute.

Your misfires are on cyls 1/3, which share a cam. You also mention a cam code. Might want to double check the timing.

It never hurts to check grounds for a clean connection.
I'm going to start with the easiest to do then work up, so first is plugs. I don't have a garage to work in at home so that makes things more difficult in the winter too. If the cam timing was off, would it run fine once warmed up though? Also, there were no problems until the weather got colder which is weird to me. By colder I'm talking around 40F.
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Old 12-02-2019, 04:26 PM   #7
viper_crazy
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Quote:
Originally Posted by smccloud View Post
I don't think my 2.5i has TGVs at all. Its like it isn't firing those two cylinders. Doesn't look to fun to get at the spark plugs with the engine in the car either

Additionally, I do remember getting a cam position sensor code and cam phaser (not sure if that is the correct name in Subaru lingo but I'll go with what I know) once. However, they have never come back and the misfire ones do. Although according to https://subaruparts.com my car doesn't have variable valve timing but I could have sworn I saw it when I had it apart.
No, you won't have TGV's, iirc. I was more so thinking along the lines that there might be a slight vacuum leak at idle when cold and it goes away as it warms because the heat causes the parts to expand and seals the leak. I should have been more specific. My apologies.
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Old 12-02-2019, 05:07 PM   #8
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No, you won't have TGV's, iirc. I was more so thinking along the lines that there might be a slight vacuum leak at idle when cold and it goes away as it warms because the heat causes the parts to expand and seals the leak. I should have been more specific. My apologies.
Ahh, ok. That is possible, the loose nut behind the wheel (me) did most of the work on the head gaskets. Although its odd that it started after it was in a shop, we had days just as cold before hand too.
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Old 12-02-2019, 07:41 PM   #9
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Not sure if this is just occuring because of something else, a symptom of a ground or what. But driving the whole 2 blocks home from Subway (stopped on my way home) Torque on my car was showing voltage of anywhere from 13.7 to 14.3 volts. Used to be rock sold at 14.3v while driving. Group d or possibly bad alternator?
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Old 12-02-2019, 08:35 PM   #10
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Intake bolts turned about 1/8 of a turn, alternator belt was a little loose. Can't check the plugs yet, don't have a socket today fits. And I think the wires might be shorting out, forgot to hook one back up and started it. It sparked right out the head of the boot (where it sucks out the valve cover) to the valve cover. Probably not supposed to do that.
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Old 12-03-2019, 02:38 PM   #11
yarrgh
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What's your coolant temp sensor reading when everything is nice and cold? It should be fairly close to ambient as well as intake temp.
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Old 12-03-2019, 07:54 PM   #12
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What's your coolant temp sensor reading when everything is nice and cold? It should be fairly close to ambient as well as intake temp.
I'll have to configure the intake temp to show in Torque, but coolant temp is close to ambient.

Tonight I didn't start it from 10 miles away like I normally do (I love my Drone Mobile Remote Start) and it was better but still threw misfire codes for 1 & 3. I am a little worried about the fact that the plug wire sparked out of the boot when I forgot to plug it back in last night. There is a good chance my parents will be coming to visit this weekend (my dad needs a new cell phone and we are all on the same plan, in my wife's name) so I'll have him bring his thin wall sockets so I can pull the plugs and look at them.

I also want to make sure I'm not looking at the engine incorrectly and that cylinders 1 & 3 are on the passenger side.
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Old 12-03-2019, 09:40 PM   #13
viper_crazy
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Quote:
Originally Posted by smccloud View Post
I also want to make sure I'm not looking at the engine incorrectly and that cylinders 1 & 3 are on the passenger side.
Correct, at least in USDM terms. Positioning is below for reference, standing in front of the car.

==firewall==
3---------------4
1---------------2
==radiator==
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Old 12-03-2019, 09:57 PM   #14
smccloud
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Ok. Not sure I'll get a cold interested temp tomorrow morning, if for no reason than I don't want to scrape windows in the morning.
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Old 12-04-2019, 07:38 AM   #15
smccloud
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Intake and coolant temps this morning were 33.8F and the outside temp was 30F.
Another thing I've noticed is that the Short Term Fuel Trim is at 0 while it's misfiring but normal idle is around -12%. Worth resetting the computer as something free to try?
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Old 12-05-2019, 11:20 AM   #16
smccloud
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Quote:
Originally Posted by yarrgh View Post
These cars tend to run well on NGK spark plugs. Those E3 plugs just look like a marketing gimmick. The spark is only going to go to one of the 3 electrodes, the other 2 are simply in the way of flame propagation. I can't guarantee that these are the cause, but they could certainly contribute.

Your misfires are on cyls 1/3, which share a cam. You also mention a cam code. Might want to double check the timing.

It never hurts to check grounds for a clean connection.
I was thinking about it this morning, and the cam timing makes sense. Oil is colder and thicker and could take longer to move the cam into the right position, didn't happen when warm. Although I don't have the tools needed to fix it at home.
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Old 12-07-2019, 04:41 PM   #17
smccloud
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Got a plug out, doesn't look great. I'll be getting new plugs for it today. I'm thinking 1 & 3 plugs were loose because there is some carbon built up on the threads and it was a PITA to get out too.
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Old 12-08-2019, 02:51 PM   #18
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Swapped out all the plugs for NGK Iridium IX plugs and it runs great again. Thanks for your help everyone.
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