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Discussion Starter · #1 ·
Hey there ClubWRX! New to the forum. So last night I was doing some mildly spirited driving (I've definitely worked the car harder) when I rolled up to a light and noticed a bad misfire. I pulled off the road and let the car cool down for about 10 minutes or so. When I started it again I had a code PO304 and COBB code PFFE. I cleared the codes with my AP and the code never came back. At first I expected the dreaded ringland failure, but after doing some reading on some of these forums I have an action plan on what I'm going to try today. First I'm going to switch the #4 and #3 coil packs to see if the issue follows the coil packs. I'm also planning on running some seafoam through the motor, cleaning the MAF, cleaning all of my grounds, possibly changing the plugs, things like that. I guess my question is, anybody have any other suggestions? I know I should be compression testing the motor but honestly I'm a little scared to :shakehead:

Another thing I wanted to ask about- while troubleshooting a boost issue (car isn't hitting target boost like it was) I noticed that the car has a Blitz SBC boost control valve on it but I haven't seen the actual boost controller inside...do people put just the aftermarket valve in there? Seems odd to me.

Car is a 2004 STi, cobb stage 2. Weather is a little crappy up here in Northern IL but I'm gonna try to do as much as possible today. Thanks in advance!
 

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Missing target boost if you were hitting it leads me to believe you have a boost leak. I had similar missfire codes when my turbo inlet was torn.

You could also have an improper map for the aftermarket parts on the car, this would lead to possible misfiring and likely engine failure. This is what torches a lot of ringlands.

I would start simple. Maf sensor usually causes a wider spread knock event, or knock that is hard to trace to a single cylinder. Check for obvious signs of leaks, then smoke test the system. It is the best way to find anything. I usually spray around with starter fluid but it's imperfect and I have missed major leaks.

Then I would pull and replace the plugs, while you are down there check compression. You can get a tester for cheap, and there are numerous write-ups how to do it. It's easy. Once you've got new plugs installed I would label the coil for cyl 4 and swap it to another cylinder and monitor that cylinder for knock. If it has insanely high knock counts compared to the other cylinder replace that coil.

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Discussion Starter · #3 ·
Thank you so much for the quick response! A boost leak also seemed most likely to me so I'll start there. I've heard spark plugs are a bit of a PITA on these cars but I've wanted to change them anyways so I'll go ahead and do so when i have nice weather or a garage to work in
 

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They are tedious because of the small area, so take your time. Seriously, don't get frustrated, use a piece of hose to thread the plugs in, it's easy to just crank them in and misthread destroying the head. You don't have an open shot like a Honda. But it's easy if you take your time.

Also check around the tgv if you have them they tend to leak after a while. JDM vehicles didn't have them, I believe they were mainly a us thing

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Discussion Starter · #5 ·
So I happened to recall the hose under the intercooler not really feeling right the last time I had it apart. I had the intercooler out because I lost some bolts under it (easy to do, as I learned the hard way). Well, the witness marks say it all. It looks like the clamp wasn't on completely whatsoever...was this my issue? I'm not sure yet, because it was fine for a couple weeks after I put everything back together. But, I could see it coming off under hard boost like I was creating yesterday. I'm going to replace the hose clamp and put it back together correctly...the hose looks fairy well worn so I'll probably order another as well... thoughts?
 

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It could be part of it.

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Discussion Starter · #7 ·
So a little update...I put a new clamp on the turbo inlet hose and it seems to be sealed up much better now. The intercooler coupler is oily and stiff so I'll be ordering one of those as well, but it seems to be sealed fairly well for now. I took the filter and MAF off, cleaned them both pretty well...the MAF looked clean but upon hitting it with some lube and a Q-Tip, it was pretty dirty. I think it was left a little damp because it started to idle unevenly once it warmed up, but after some driving it seems to idle perfectly. I got about 1/4 mile from my house when the CEL came back on for the same thing, cleared it with the AP and it hasnt come back at all. Idles smoothly, and is misfiring waaay less. For peace of mind I'll most likely change the plugs and do a compression test tomorrow, but I'm quite confident it was a boost leak or dirty MAF....phew.

As for my boosting issue...I'm suspecting the Boost Control Solenoid but I'm not sure. WGDC seems to be normal so I think the wastegate is acting as it should...but it doesn't hold boost anywhere near what it used to, and it doesn't boost as high either. It'll go up to around 16 and hold there if I give it some time between shifts, but when I shift quickly like I used to, it looses basically all of its boost and will only boost around 7 psi (wastegate pressure I think?). Sometimes it'll also spike to around 17.5 and then go all the way down to 7 too. As you can probably tell, I know my way around a car but I'm completely new to both the Subie and Turbo worlds. Thanks so much for your responses thus far, if I could troubleshoot this boost leak I'd be happy as could be!
 

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Discussion Starter · #8 ·
When I was out for my test drive I also grabbed some brake parts cleaner...best stuff to clean most sensors with on these cars, correct? TIA
 

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I would use maf cleaner on the maf.

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Discussion Starter · #11 ·
Somebody PLEASE help me out here! It's 3am and I can't mess with the car any longer. I got 4 new oem replacement spark plugs and threw them in the subie tonight while also checking the compression on all 4 cyls. everything seemed to go together just fine but I couldn't get the #4 coil to really feel like it was seating well. Anyways I got through the rest of them, started the car up, and BAM, misfiring like crazy. Would barely stay running under load and idled like crap :( something i noticed that was odd was, the misfires would stop when i let off the gas or between shifts. it even revs all the way to the redline when it's not under load...I was thinking maybe i broke a wire to the coil on accident but it doesnt make sense that it'd be smooth as silk on decel and when not under load...
 

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What were the results of your compression test, did you look for leaks around the tgvs, intercooler to throttle body hose and turbo inlet?

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Discussion Starter · #13 ·
100 on every cylinder, cold. I've heard the engine being warmed up makes a huge difference in these cars. No leaks...car ran fine when i pulled it into the garage to do plugs. Just weird to me how it'll completely smooth out when not under load or under decel
 
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