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04 ForesterXT 5MT
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395 Posts
Discussion Starter · #1 ·
I was hoping to get some insight regarding my CEL. I've had it checked twice and both times it comes back as P00304 (Cylinder 4 misfire).

My question is has anyone had any experience with this same code? Also where did you start when fixing it? (Spark plugs, wires, coil packs) Any insight you can provide will be very helpful and appreciated!!
 

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Administrator
2004 Forester XT Premium 4EAT
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29,432 Posts
I'd start with checking the plugs/coils. No wires on the FXT, it's coil-on-plug design. Hopefully it's that easy a fix and not something more serious like a blown ringland.
 

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04 ForesterXT 5MT
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Discussion Starter · #3 ·
Ok, that's what I thought. Is there a way I can test just the plugs and coils?? The car has 156k on it and I did the plugs @ roughly 110k. Do they go out that quick?? What does a blown ringland mean??
 

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2009 Foz XT Limited Auto
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369 Posts
Do as Tuned said. I had a shot coil and didn't want to start tearing down the '09 to test coils (due to various reasons I won't mention). Turns out I should've because the coil was done for (visually it looked bad).

Edit: This happened after a recall done to the turbo oil supply line this summer (yes, the same recall that stopped sales back when the SHs were first released, for some reason it was never fixed on my car...). When 75-100% throttle was applied, I was getting misfires under boost (harsh hesitation, racecar-redlining-like sounds from the outside), then the cluster would light up. The car is 100% stock.
 

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luvin' it
2008 Forester Sports XT 5-speed manual
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815 Posts
I recently resolved my P00304 issue on my 2008 Forester Sports XT. I had a slight hesitation during cold starts and at idle. My mileage was at around 147k miles. The P00304 code would pop up every few hundred miles after clearing the code with an AccessPort. I did all the "easy" fixes - swapping coilpacks, replacing plugs, and replacing the cylinder 4 coilpack. Nothing addressed the issue, so I agreed with my mechanic to take the engine out and do a thorough inspection.

In the end, it turned out to be valve lash. A bucket was replaced and it solved the CEL issue. My idle is smooth with no more hesitation.

I hope that helps,
Andrew
 

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04 ForesterXT 5MT
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395 Posts
Discussion Starter · #7 ·
Thank you all for your insight/help. I really appreciate it!

My next question is: should I not be driving the vehicle? This is my daily driver and I do have access to another car but I won't have time to look at this issue until this weekend.

If I'm able to do what Tuned said, and it doesn't fix it; will the compression test tell me what I need to know??
 

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Premium Member
2017 VW Golf SportWagen 5MT
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How is your oil consumption? If the code stays on that cylinder, it could be cracked ringland or a valve sealing issue. Leakdown test should confirm that if it's the case.

Stan
 

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Discussion Starter · #9 ·
The code has been on # 4 twice. It came on last week on Thrusday and I had it tested (P00304) and had it reset then. It just came on again last night, and had it checked again today and it was the same code! (P00304)

As far as I know, oil consumption is good. I check the level on every fill up and it doesn't fluctuate a whole lot and I do changes every 3750... I'm wondering if I should just do a leakdown test first. I'd hate to go through and swap plugs and coil packs and still get the same code...

Thoughts?? Should I be driving the car???
 

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2005 Forester XT Auto -> STI
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96 Posts
My forester had a po304 when i purchased it i swapped coils replaced a coil and plugs. After Fighting for a couple weeks i purchased a set of used injectors and replaced my #4 fixed my problem and everything has been great.
 

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Discussion Starter · #11 ·
My forester had a po304 when i purchased it i swapped coils replaced a coil and plugs. After Fighting for a couple weeks i purchased a set of used injectors and replaced my #4 fixed my problem and everything has been great.
See I've heard and read it could be the injectors too. Is the only way to diagnose this by process of emlimination?? I would hate to do all that work on the plugs and other stuff and have it not fix my issue. I'm lost because like I said its my DD and I don't want it to be out of commission longer than needed.
 

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2009 Foz XT Limited Auto
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Gotta go by elimination. A misfire can be a whole ton of stuff.

Here's a pretty good guide... lol

If You Have A Misfire Code Please Read This! - NASIOC

Easiest 1st thing would be to swap two coils. Then reset the ECU, and see if the code changes cylinders. If it goes to the "new" cylinder then you found your issue. If it doesn't, gotta dig more - spark plug, injector, compression, leakdown, valves, ringland, etc. You could also check to make sure the PCV valve still works correctly.


Can you feel it misfire? Do you see the check engine light flash? If it does, how often?

You need to fix it rather quickly because it can lead to more damage. But if it is not constantly misfiring, I'd say limp the car around and stay out of boost, or whatever situation makes the car heavily misfire. But that gotta be fixed, before it leads to other issues.
 

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Discussion Starter · #13 ·
Gotta go by elimination. A misfire can be a whole ton of stuff.

Here's a pretty good guide... lol

If You Have A Misfire Code Please Read This! - NASIOC

Easiest 1st thing would be to swap two coils. Then reset the ECU, and see if the code changes cylinders. If it goes to the "new" cylinder then you found your issue. If it doesn't, gotta dig more - spark plug, injector, compression, leakdown, valves, ringland, etc. You could also check to make sure the PCV valve still works correctly.


Can you feel it misfire? Do you see the check engine light flash? If it does, how often?

You need to fix it rather quickly because it can lead to more damage. But if it is not constantly misfiring, I'd say limp the car around and stay out of boost, or whatever situation makes the car heavily misfire. But that gotta be fixed, before it leads to other issues.
Okay,thank you so much for your help. It's starting to make more sense on how I can move forward...

I feel really dumb for asking this but... what would a misfire feel like?? Do I need to be in boost or will I feel it in vaccum too??
 

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luvin' it
2008 Forester Sports XT 5-speed manual
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815 Posts
I want to add that a compression/leakdown test may not provide conclusive findings for the misfire. In my situation, my compression numbers were fine for all cylinders. I had no unusual oil consumption issues. The problem couldn't be definitively found without pulling the engine and looking at the block.

Nonetheless, I hope your problem has an easy fix!
 

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2009 Foz XT Limited Auto
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In my case the misfires were feeling like heavy stuttering. Something was not right. The engine sounded like it was making popcorn, literally. But not all misfires are like that. Does the car have a rough idle?
 

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04 ForesterXT 5MT
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Discussion Starter · #17 ·
Just got done swapping coils. I'm going to wait a few days and see if I get another code. It's my daily driver so if something is going to happen I anticipate it happening within a short time frame. I'll keep the thread updated with my info. Thanks again for all the insight!!
 

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Discussion Starter · #18 ·
Okay so my light came back on today when I was out for lunch. I went to get the code ran and its the same P00304. I'm unsure on what or how to check the next thing??
 

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2005 Forester XT Auto -> STI
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to me this was my same problem. so now its prob not coil related possibly a bad plug, injector or deeper engine issue.
 

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Discussion Starter · #20 ·
to me this was my same problem. so now its prob not coil related possibly a bad plug, injector or deeper engine issue.
That's what I was thinking. Is there a quick way to test plugs & injectors? I don't want to go out and buy all these parts and still get a code.. Seems like a misfire is one of the hardest things to pinpoint. I'm thinking I might have to take to someone who can figure out what is causing it.
 
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