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Old 01-20-2021, 12:17 AM   #1
demid30
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Default Replaced pcv valve and 2 days later CEL

So I replaced my pcv valve on my 2014 WRX, on Sunday, and this morning, 2 days later I get a check engine light with code p0304. Do you think it's related to something with the pcv I just replaced or is it a big coincidence that it's something not related to that? I had no CEL prior to replacing pcv. It seems to only be misfiring at idle. So frustrating.
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Old 01-20-2021, 08:05 PM   #2
demid30
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I changed cylinder 4 coil and code is still there. I didn't do the plug since it only has 50k miles on them. But now I'm pissed I didn't do it while I had everything apart. Anyone think it's related to pcv?
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Old 01-20-2021, 11:46 PM   #3
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50k miles on spark plugs, even if you say you are using iridiums, is a lot. I would replace all spark plugs and go from there. That should eliminate if they are related or not.
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Old 01-21-2021, 08:02 AM   #4
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yeah the whole 100K miles hype doesn't hold up under boost.
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Old 01-21-2021, 09:48 AM   #5
Elbert Bass
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Quote:
Originally Posted by GeoNV View Post
yeah the whole 100K miles hype doesn't hold up under boost.
Don't know where you're getting 100k miles - Subaru spark plug service interval for that model is 60,000 miles.
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Old 01-21-2021, 12:11 PM   #6
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the sales and marketing material. not Subaru specific.

If you do a generic search on google you'll see 100K miles pretty often. Obviously with a turbocharged application that period decreases- NGK says 40-60k if lightly modified and less with more modifications.
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Old 01-21-2021, 04:59 PM   #7
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Quote:
Originally Posted by demid30 View Post
I changed cylinder 4 coil and code is still there. I didn't do the plug since it only has 50k miles on them. But now I'm pissed I didn't do it while I had everything apart. Anyone think it's related to pcv?
After swapping the coil pack, the code is still there. The next step is swap the injector with another one from the engine and see if the CEL follows.
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Old 01-21-2021, 07:20 PM   #8
demid30
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Quote:
Originally Posted by GeoNV View Post
the sales and marketing material. not Subaru specific.

If you do a generic search on google you'll see 100K miles pretty often. Obviously with a turbocharged application that period decreases- NGK says 40-60k if lightly modified and less with more modifications.
Yea I've heard 100k also. I know Subaru recommends 60k. I knew I should have replaced the plug when I was in there to know if that was it. Trust me I'm kicking myself for not doing it.
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Old 01-21-2021, 07:22 PM   #9
demid30
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Originally Posted by Max Capacity View Post
After swapping the coil pack, the code is still there. The next step is swap the injector with another one from the engine and see if the CEL follows.
I guess I'll try this before doing the plugs
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Old 01-22-2021, 08:47 AM   #10
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I guess I'll try this before doing the plugs
If I read this right, youre going to swap injectors to see if the code follows? I just did injectors on my 08 and that job is waaay more involved than doing spark plugs. Next step would be to just replace the spark plugs before you dive into swapping fuel injectors. 60k miles on them, you need new ones anyway so it wont be a waste of time if that ended up not being the root cause.
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Old 01-24-2021, 04:08 PM   #11
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Ok so I replaced all 4 spark plugs today and I did my air filter too as it also needed replacing. The spark plugs definitely needed replacing. Cylinder 4 spark plug was noticably worse then the other 3. So I go to check code and on torque pro it already was saying that my cylinder 4 misfire was fixed, it was highlighted in green with a check mark now saying historic code, which to me means it was now fixed. I cleared anyways and started car. It fired up great and idled great but 5 minutes later CEL started blinking again, but only cel this time, no cruise control and traction control lights flashing now. So I check code and it's the same P0304. So I say to my self I better check this PVC again. I take intercooler out and get the PVC out and guess what, the valve doesn't even rattle anymore. I tried cleaning it, it starts to rattle but then it won't rattle anymore. So I have to get a new PVC but have to wait to Subaru is open. What would cause this to happen to the PVC in 2 days?
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Old 02-04-2021, 10:55 PM   #12
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So I replaced the pcv again, but I still have the p0304 code. I did all 4 plugs and the coil on cylinder 4. Anyone have any ideas for me? The car fires up and idles great and then if I give it gas when the rpms drops you can feel it misfire and almost stall out. Anyone have any insight for me? I'm so frustrated. Can I do a log somehow and figure out what's wrong?
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Old 02-05-2021, 09:19 AM   #13
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Time to do a compression test. I would think that if you had a vac leak that you would have multiple misfire codes and or other codes. It being isolated to that one cylinder, I would check compression on that cyl first. Simple checks/work on normal cars like changing spark plugs and checking compression becomes a pain in the ass with these cars. I dreaded doing compression check on my car.

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Old 02-05-2021, 10:24 AM   #14
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just an idea- is the fuel pressure regulator boost reference line deteriorated? It plugs into cylinder 4 intake runner.
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Old 02-06-2021, 12:18 AM   #15
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+1 on compression test. Best of luck
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Old 02-10-2021, 04:35 PM   #16
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Agreed on the CT. I feel for you.
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Old 02-26-2021, 10:29 PM   #17
demid30
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Quote:
Originally Posted by Mindriddle View Post
Time to do a compression test. I would think that if you had a vac leak that you would have multiple misfire codes and or other codes. It being isolated to that one cylinder, I would check compression on that cyl first. Simple checks/work on normal cars like changing spark plugs and checking compression becomes a pain in the ass with these cars. I dreaded doing compression check on my car.
Yes simple stuff on this car is not simple! So I decided to take it to Prime Motoring, they are supposed to be one of the best shops for Subarus here in New Jersey. Plus there 2 miles away from where I live. They did compression test right away. 10 psi on cylinder 4! And leak down was really bad, like 90% at the valves and crank case. So they basically told me I need a new engine. They said, for them to take it out, find the problem, and rebuild it would end up costing close to 10k, because they don't cut corners. And That it would be way cheaper to just drop in a used Ej25 or a jdm Ej20x. But the used ej25 are like 5k! The Ej20x are half that. But then they need to professionally tune it and what not. What do you guys suggest to do? I don't know what I'd get if I sold it like this. I love the car though really don't want to get rid of it.
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Old 02-26-2021, 10:34 PM   #18
demid30
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Quote:
Originally Posted by GeoNV View Post
just an idea- is the fuel pressure regulator boost reference line deteriorated? It plugs into cylinder 4 intake runner.
I don't think so, but thanks for the idea! It's got 10 psi compression in cylinder 4 and 90% leak down in valves and crank case
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Old Today, 12:45 AM   #19
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Best of luck to you!
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