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Old 08-18-2013, 04:09 AM   #1
kanga-ru-45
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Default Very curious misfire, now no misfire? 2006 wrx

Ok guys did a search and couldnt really find a situation like this.

A little background. Took it in to get diagnosed for a cyclinder 4 misfire. They found that a melted wire harness was the culprit. Put a new one in. Ran GREAT. Also was getting a code for secondary airpump. Got that replaced, code came up for catalytic converted after that. (Mech said it might happen) cleared it out never came back and has been driving great for three weeks (drove it about 1k miles in one day from Seattle to Salt Lake with no issues).

So today I start it and start driving and pull up to a stop light. The car idle drops to like 500 rpm and starts shaking and the check engine light comes on and starts blinking...

So I drive a few blocks to my buddys house. Check the replaced wire harness, not melted. Start it back up and it seems that the rough idle is gone and now the check engine light is solid with cruise flashing.

Went and got the code read and says a cyclinder 4 misifire. They wouldnt let me clear it out due to some rule. The car seems to be running fine now.

How can I have a misfire, then the misfire go away??? Culprit?

Please help.
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Old 08-18-2013, 07:03 AM   #2
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get the code(s) scanned

post the codes

forget the verbage....just the codes
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Old 08-18-2013, 01:18 PM   #3
kanga-ru-45
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Po304...
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Old 08-18-2013, 04:55 PM   #4
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What more do I need to do to get feedback?

I read through some people having issues with a misfire potentially being bad gas. My tank was getting pretty low when this happened. I went and filled up at a different gas station today (chevron). Bought some seafoam, going to add that after my tank isnt completely full.

Also went back and looked through previous owners receipts. Says "R&
R fuel injectors, 02 sensor and belts. The item list says serpentine belts, fuel injector, spark plug... among other irrelevant things. about 1500 miles ago

A little help?
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Old 08-19-2013, 11:37 PM   #5
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Thanks for all the help guys.
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Old 08-23-2013, 12:09 PM   #6
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The misfire and code went away on its own then came back today. Going through previous owners receipts says injectors were replaced.

I recently took it in to fix the misfire on this same cylinder, the culprit being a melted wire harness. replaced it and it ran fine. Do you think that the previous owner may have been driving it with a misfire, causing the catalytic converter to go bad and thus my problem now?

Come on guys I need some help...
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Old 08-23-2013, 05:23 PM   #7
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mileage and valve check status ?
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Old 08-23-2013, 09:15 PM   #8
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Get a compression test if you haven't yet. I was having the same problem when I bought mine, ran fine the first few weeks after I bought it, then I started battling misfire codes left and right. I did everything I thought would solve the problem, no fix, CEL kept coming back. I took it to Subaru and they did a compression test only to find out I had burnt exhaust valves. Hopefully that is not your situation. Normal compression should be about 135-140 cold and about 170 hot if I'm not mistaken.
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Old 08-24-2013, 02:12 PM   #9
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76,000 miles on the car compression test was good three weeks ago

1-170psi 2-170 psi 3-165 psi 4-165 psi

(Thanks for getting back to me)
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Old 08-25-2013, 09:08 PM   #10
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Update:

Swapped the coil pack from cylinder 4 to cylinder three and there was still a misfire. As I was sitting in my car cursing it smoothed out and the misfire stopped?

After disconnecting the battery again to put the battery tray and heat sleeve on it (dumb) no more code. Drove it all the way to autozone and it never came on and no code to read. So I was not able to determine if cylinder 3 was misfiring so i am not sure if it is the coil pack or not.
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Old 08-27-2013, 11:00 PM   #11
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What kinds of mods are on the car? Is there a chance that the previous owner had parts installed on it and took them off when he sold the car? If that is the case he may have had the car tuned to support those mods, then left the tune on if/when he put the OEM parts back on. Three weeks is plenty of time to lose enough compression I think, mine went pretty quick. If you have a Subaru dealership near you, or perhaps a tuner, I would contact one of them and see if they can check the ECM for a tune, mine was tuned, and I had no idea it was. After all the hassle I went through to fix my mifires, which resulted in having to buy a new ECM, I had the mechanic flash the stock tune to the car.

Hopefully if the car was tuned, they did not run it too lean, sure it makes it faster, but burnt exhaust valves are definitely not worth it.

Also, does your engine temp gauge on the dash ever move up at all, outside of normal operating temp? Normal temp should be between the two middle lines.
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Old 08-28-2013, 02:05 AM   #12
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plug gaps ?
I suffered some knocks after doing a valve adjustment, I was sure my problem was solved as the plugs only had 20k on them (stock iridium). When my tuner checked they looked "unhappy" and were at .042, new plugs set to .028 and things were better than they have ever been. A minor step I overlooked was bugging me for 6 months.
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Old 08-31-2013, 02:53 PM   #13
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Hey guys,

Car is absolutely bone stock. The only thing after market is a wire harness repair that was done when the wireharness to the injectors melted somehow.

But a little update. Took it to a shop and they found 100psi compression on all 4. Seems a little low to me. Had one done 4 weeks ago at sea level and it was 160-170 psi an all 4. now in Utah at about 4500 feet its 100 psi, maybe due to elevation?

Any way. He found that cylinder 4 had an autolite spark plug while all the other were NGK. Someone befor me was obviously trying to diagnose the problem and threw an autolite spark plug in. So he put an NGK in and the problem went away.....until the next day.

Fired it up and misfired for about 30 seconds then went away. Drove it to work no problems. This morning it is back and will not go away.....GRRRRRRR I HATE THIS CAR!

(It's not plugs, its not coilpacks)

The temperature guage does move, it goes right up to just above the 1st line, a bit less then half way in the middle and ive never seen it budge any higher. Also due to the car being stock I cannot imagine it has been custom tuned. It was owned by a boring married couple with kids who gave up on it and sold it to me for cheap.
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Old 08-31-2013, 03:16 PM   #14
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100 psi on all four is low, even for a cold engine. You might want to take your car to Subaru and see what they say. If you are in Utah Mark Miller does good work, they helped me out with the issues I was having with mine.

Sounds like a valve issue to me, compression going that quick is not a good thing. The elevation shouldn't change it that much, if any.
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Old 08-31-2013, 04:02 PM   #15
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Quote:
Originally Posted by mdleonard1434 View Post
100 psi on all four is low, even for a cold engine. You might want to take your car to Subaru and see what they say. If you are in Utah Mark Miller does good work, they helped me out with the issues I was having with mine.

Sounds like a valve issue to me, compression going that quick is not a good thing. The elevation shouldn't change it that much, if any.
Ok thanks man. I have been thinking about just bucking up and taking it to a dealership. Even if it means i need to pay more, i just want it taken care of. Tired of all these small shops with their "guess and check", "wait and see if it comes back BS."
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Old 09-06-2013, 10:55 PM   #16
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UPDATE for anyone who cares.

Befor i start let me start off by saying that Solid Auto works is a great shop and I am confident that they will get to the bottom of this issue.

With that being said, took it to solid auto on thursday morning and they returned it to me that afternoon after they had replaced the fuel injector (which they didnt charge me for because they had a used one lying around). Drove great! They had even driven it around and stuff at lunch to make sure it was good to go. So, drove it home. The next morning drove it to work. Everything seemed ok. Although i did notice a very small shudder at idle, hardly noticeable but this is what made me think it was not fixed, I have noticed this stutter after i have gotten it back the last 3 times it was "fixed"

So I get out of work and what do you know?! My good old friend the misfire is back. So I limped her on back and parked it at the shop.

A guy in my original post thinks that the initial wiring repair for the melted wireharness to cylinder four might have a cold solder point interfering with the current.

Well.....im at a loss. Not spark plug, not fuel injector, not coilpack, leak down test came back good, compression is goodish (100 psi)....
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Old 09-07-2013, 03:22 AM   #17
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Do you know if the heads have ever been removed?
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Old 09-07-2013, 06:25 AM   #18
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I'm going to just through this out there and it may or may not be the problem, but I had a very similar issue and it did in fact end up being the plugs. It so happens that I had originally had the plugs changed thinking it was the problem and they either didn't change them or they dropped one of the new plugs. After exhausting my options on the dang misfire I checked the plugs myself and one of the ceramic collars( white part) had a hair line crack that wouldn't initially misbehave unless the engine was at op temp. My advice is visually inspect the plugs this time. That crack was not easily seen.
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Old 09-07-2013, 03:06 PM   #19
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Quote:
Originally Posted by Scary View Post
Do you know if the heads have ever been removed?
It is possible they were removed before I bought the car. I know the people who owned it were struggling to find out the problem just like I am now. Thats why they sold it to me for 3000 dollars. I still think it was a killer deal but....less so now...thought it would be something simple
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Old 09-07-2013, 03:08 PM   #20
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Quote:
Originally Posted by myblusti View Post
I'm going to just through this out there and it may or may not be the problem, but I had a very similar issue and it did in fact end up being the plugs. It so happens that I had originally had the plugs changed thinking it was the problem and they either didn't change them or they dropped one of the new plugs. After exhausting my options on the dang misfire I checked the plugs myself and one of the ceramic collars( white part) had a hair line crack that wouldn't initially misbehave unless the engine was at op temp. My advice is visually inspect the plugs this time. That crack was not easily seen.
Thanks for the input but the car doesnt behave at any temperature. Unless we change something, then it will behave for a day and say "ok that was fun, time to start misfiring again"
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Old 09-07-2013, 05:20 PM   #21
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100psi is low, no matter what, fully built to the hill motors completely cold will be at 115-125 so either way that's off a bit.

The wiring issue, it might have corrupted the ECU. We had an instance where a faulty engine replacement (and build) had prompted the wiring harness to have issues due to incorrect grounding and what not. Regardless, the vehicle's harness was replaced and everything seemed fine for about 2 weeks, the humidity kicked up (Chicago area) and guess what, misfires started to come back. Replaced ECU with another factory unit and all was well. That's not to say you should just replace your ecu but what you should do is long term logging and data acquisition with a Snap on or Matco scan tool so that when the event occurs you can see where it was picked up from.

Another situation was a wiring replacement due to the harness melting, but remember that when it melts there's a reason, the wiring is insulated so that it doesn't have that issue and if there is a tremendous spike in excessive, un-used voltage going through the harness then you need to trace back as to why. This may mean going as far back as the ECU, fuses, cutting the loom open to see where else there are issues because there will be issues. Even if you have a "fix" it'll be temporary as there's still a root to the cause.

There are amplifiers and resistors in the ECU that may have faulted due to the wiring fire.

You may have damages to the harness further down as well, which is why I sated that the look might have to be split and trace back the "hot wires".

You're not going to find the answer here, either let the shop do there thing and pay up, hire an automotive electronics and diagnostics specialist and pay up or find the docs for the wiring of the vehicle and all it's schematics and get ready to bloody up your knuckles, get some aches in the low of your back (from hunching over the wiring) and some sore finger tips from cutting the loom.

Your elevation change won't put the compression that far off either. Plugs, yes, but I'm sure they checked them when they did your test there. Injectors, that's sort of evident when your only running on three cylinders.

-Mark
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Old 09-07-2013, 07:32 PM   #22
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Wow Mark thanks for the awesome reply. That has been my concern the entire time. What caused the melted wiring in the first place. Simply replacing the wiring is just a band-aid, just because you cant see the issue doesnt mean its not there.

An electrical problem has been my hunch the whole time but im not a mechanic or an electrician so, looks like I might be paying someone to figure this out.

Just out of curiosity how much might a working (used?) ECU cost?
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Old 09-07-2013, 09:00 PM   #23
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What Mark said could be true, you could try to find one at pick and pull or something. Although that might only solve one part of the issue. It may be a temporary fix, but if your compression is that low, and gauging that it decreased that quickly, there is likely more to the scenario.

If you get a new or used ECU, you would still need someone to program it to the car, I know Subaru can do that, but I'm not sure about anyone else. I highly suggest taking it to Subaru, I wish I would have with mine instead of dancing around for three months with no success.

I don't have any affiliation with Subaru or anything, so I am not trying to get you to go there to make any money. I just know that they helped me greatly, and I'm trying to recommend the best advice I can give.
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Old 09-07-2013, 09:19 PM   #24
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you should know that you are not the only one having this issue. i have an 07 wrx and have had this issue now for a while.

misfires at idle. probably about 1-2 times per week. never does it when driving normal. ive changed plugs, injectors (have not changed coil packs), and still happens. either cylinder 1 or 4 most of the time.

cant figure it out, have no idea. really irritating but have been living with it.

i am in for an answer if you figure it out.
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Old 09-08-2013, 12:12 AM   #25
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Yea. I'm afraid your going to have to get your hands dirty or your wallet light on this one. On a positive note I wouldn't worry a ton on the compression as all the numbers are relatively close across the board correct? It could just be the compression gauge or maybe the guy didn't have it at wot when checked. But the main thing is there all within 5% of each other. I think like one of the previous posters said its probably in your harness or ecu somewhere. Could be as simple as a bad ground. Unfortunately those can be the hardest things to find. The only thing I can add is pull the harness and check it. It will suck, but you may fix your issue and not even realize it. Then again you may not. Good luck man. If you were close I'd help.
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