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Old 03-08-2019, 10:55 AM   #1
Davidmaguirre
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Default I donít know what else to do? Please help!

Hello everyone! So hereís the story. I was getting a P0304 code (misfire cyl. 4) on my 2009 WRX. I switched out the spark plugs and coil pack. I switched the coil pack with another one to see if the code would change. It didnít but I still put in a new one just in case. I got a compression test done and it passed with flying colors. Still got the code so I brought it in to a local shop that are known (in a good way) for their work. They charged me 90 dollars for a complete diagnosis of the code. They told me they were certain it was the coil pack. I told them what I previously did but even so, let them do the work to switch it out again. I drive it back home and then the next morning the light comes back on with the same code. I let the shop know, and bring it back to them. They then did an injector service along with a top engine clean. I drive it home then once again, the next morning the light comes back on. I bring it back to the mechanic and they swap out injectors for new ones. Once again, I drive back home then today in the morning the light goes back on with the same code! At this point we have no idea what it could be. The car runs fine as it normally does with no obvious issues. Do you guys have any suggestions or ideas as to what can be causing this? Any input is very much appreciated! Thank you!
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Old 03-08-2019, 11:38 AM   #2
Jay11STI
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So what were the compression test results on all 4 cylinders? Was a leakdown test done?
Whats mods does the car have and how many miles?
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Old 03-08-2019, 03:48 PM   #3
Davidmaguirre
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Quote:
Originally Posted by Jay11STI View Post
So what were the compression test results on all 4 cylinders? Was a leakdown test done?
Whats mods does the car have and how many miles?


I canít recall exact numbers. I have it documented though. I just remember that compression was great. A leak down was not done. The car is completely stock. Itís riding on over 120k miles and all 100k maintenance was done. The car has been babied all its life..
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Old 03-08-2019, 07:55 PM   #4
ironpants
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I would verify the spark plug gap. I don't know how the ecu determines this code, but try cleaning off your crankshaft and camshaft sensors, as ferrous material could functionally interfere.
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Old 03-08-2019, 08:03 PM   #5
Blktrax
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Read here

https://forums.nasioc.com/forums/showthread.php?t=2550077
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Old 03-08-2019, 09:50 PM   #6
DrD
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have you checked for pin fitment in the connector to the coil pack? Haven't had this issue on my Legacy, but on our old Odyssey, I was chasing a misfire - it was on cylinder 4 - I swapped the coilpack between 4 and 5 - misfire stayed on 4, swapped the plug from 4 - 5. misfire stayed on 4. pulled the intake plenum and swapped injectors around, misfire stayed on 4 - also cleaned the injectors (they were gunked up on the nozzle plates) while I was at it, which didn't help. Was going bananas, started pulling at the harness and could make it come and go - looked inside and one of the sockets in the connector was damaged - bought a new pigtail, swapped it out, and the problem was solved...
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Old 03-08-2019, 10:18 PM   #7
Jay11STI
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If compression test results were good then the bottom end of the engine is fine. A leakdown test would determine if there is a valvetrain issue. Having bent or burnt up valves can cause a misfire. At 120K this is a possibility.
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Old 03-10-2019, 07:08 PM   #8
igoiks
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Do a leak down teat, i had prefect compression with blown ringland
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Old 03-10-2019, 08:26 PM   #9
the_saintusa
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Had a misfire that ended up being a bad fuel injector electrical connection.
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Old 03-10-2019, 09:25 PM   #10
jamal
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Quote:
Originally Posted by igoiks View Post
Do a leak down teat, i had prefect compression with blown ringland
I have seen this a number of times. Should have been done at the same time as the compression check.
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Old 03-11-2019, 12:24 PM   #11
Jedi03
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am fixing same issue on a Nissan quest...injector wiring is bad on 2 cylinders and still chasing down o2 sensor wiring...other note had random on my sti yester cyl 3...suspect bad fuel as it went away after filled up..had run down to 1/3 tank due to errands...usually fill up at 1/2, spark plug was good, not sure if coil pack connector was loose, threw some dieelectric grease in both sides of the col...did see a rust spot on the spark plug so could have had water in the fuel, no issues still since fill up
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Old 03-11-2019, 11:24 PM   #12
A.S.N.F.
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Quote:
Originally Posted by Jedi03 View Post
am fixing same issue on a Nissan quest...injector wiring is bad on 2 cylinders and still chasing down o2 sensor wiring...other note had random on my sti yester cyl 3...suspect bad fuel as it went away after filled up..had run down to 1/3 tank due to errands...usually fill up at 1/2, spark plug was good, not sure if coil pack connector was loose, threw some dieelectric grease in both sides of the col...did see a rust spot on the spark plug so could have had water in the fuel, no issues still since fill up
If you suspect water in the fuel make sure not to run ethanol (like 10% only added) for a while. Ethanol absorbs water and makes fuel separate. I turned wrenches for 5 years after tech school (then going back to school again) and I live in Nebraska where we see this happen a lot. Run the tank to about an eighth, drain the tank, swap the fuel filter (water REALLY likes to hang around in there some how) and then fill it up with good pure gasoline.

Full disclosure I was not a Subaru tech, Toyota and Dodge so I don't know Subaru's that well.
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Old 03-24-2019, 10:17 PM   #13
Davidmaguirre
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Default I donít know what else to do? Please help!

Leak down passed. Iím running out of options. I guess the next step would go to the dealer? Both of the shops I go to are at a loss as to what to do.

Last edited by Davidmaguirre; 03-24-2019 at 10:29 PM.
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Old 03-25-2019, 09:15 AM   #14
Charlie-III
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Quote:
Originally Posted by Davidmaguirre View Post
Leak down passed. I’m running out of options. I guess the next step would go to the dealer? Both of the shops I go to are at a loss as to what to do.
Have you tried checking the harness to coil and injector connections?
You have obviously ruled other bits out, but a couple have mentioned a possible harness connection.

Do you actually feel a misfire? I have a phantom one on my car, cyl 4, did almost everything you did as well.
I don't feel the misfire, may be EGR related since that's where the tube goes into the intake.
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Old 03-25-2019, 11:04 AM   #15
Jedi03
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update for self if helps point in the right direction...slaved the 2 injectors to the one next to it which corrected misfire, still working on o2 code...suspect bad ecu or more wiring problems...sti has no further issues at this time, to avoid a lot of these problems i don't run e85 just pump 91...
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Old 04-14-2019, 08:28 PM   #16
Jaya1c
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Anyone else tired of STIs ECU?
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Old Yesterday, 01:23 PM   #17
Davidmaguirre
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Default I donít know what else to do? Please help!

Thanks for the additional help. The mechanic is directing me towards the dealer$hip him and a tech at Subaru feel that it MAY be a ďmiss-guided valveĒ. I would hate to pay and find out that wasnít the case. I donít feel any kind of misfire or fowl play in my day to day driving
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Old Yesterday, 02:01 PM   #18
Charlie-III
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Silver Sleeper BK, 5MT

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Quote:
Originally Posted by Davidmaguirre View Post
Thanks for the additional help. The mechanic is directing me towards the dealer$hip him and a tech at Subaru feel that it MAY be a ďmiss-guided valveĒ. I would hate to pay and find out that wasnít the case. I donít feel any kind of misfire or fowl play in my day to day driving
WTF?
I will "guess" what they mean is a dropped valve guide.
A dropped guide (usually found with a leakdown test) may be "seen" by dropping the exhaust manifold and possibly removing the intake manifold. Then, look.....
Again, this would likely show in a leakdown test.
A compression test may show a soft cylinder, but that could be valves, rings, ringlands or a dropped valve guide.
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