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Old 03-23-2015, 12:33 AM   #1
billyboy999
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Default Something broke at the track, exhaust is popping, low on power, terrible fuel economy

I have a 2007 STi with built short block, mild cams, catless exhaust but otherwise equivalent-to-stock turbo/heads. I went tracking today and something broke.

Symptoms: Car runs, but extremely rough. Exhaust pops (soft pops, not gunfire bangs) constantly when you're trying to accelerate or cruise at freeway speed. Car is down on power. For ex. boost gauge reads 0 PSI but the exhaust is popping, not getting any power. Can't seem to make much boost either. Fuel economy is really bad (so it's pumping in fuel but not making any power from it). No codes thrown. Tried to reset the ECU, no luck.

The problem actually started during tracking but it was driving fine and made full power, so I didn't think much of it. But when I drove it home from the track it was sketchy. My friend behind me saw flames at one point; my car doesn't normally make flames.

I am going to take this to a shop but I wanted to see if anyone had any guesses.
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Old 03-23-2015, 12:48 AM   #2
Uncle Scotty
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oh boi

did ya think ya mighta blew a charge pipe coupler?
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Old 03-23-2015, 12:48 AM   #3
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and you maybe should sell it quick
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Old 03-23-2015, 01:07 AM   #4
billyboy999
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I've got stock turbo/IC, I took a peek at the tubing, looks ok... I'm not running super amounts of boost either.

And no, I don't want to sell this car Hell, if the engine needs to be rebuilt I'll pay up.
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Old 03-23-2015, 01:47 AM   #5
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Stuck intake valve maybe? Symptoms include all the things you mentioned. Do you have a rough idle speed?
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Old 03-23-2015, 01:52 AM   #6
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Might be a little too much at this point but you can pull the heads and pour gas onto the valves to see if they are creating a proper seal, I had a SBC that had an intake valve problem, and did the same exact thing.
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Old 03-23-2015, 02:50 AM   #7
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if its something, im sure a code will throw. maybe let it idle for like 20 min in the driveway.
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Old 03-23-2015, 09:36 AM   #8
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I was thinking a valve problem is most likely. Maybe exhaust valve because of the popping noises. Unfortunately I don't have the tools nor skills to do any engine work so it's going to the shop regardless.

The weird thing is no codes. I drove it 2hrs back from Thunderhill... Drove like **** all the way back but no codes...
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Old 03-23-2015, 09:53 AM   #9
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ok...not seeing boost is the tell....and if this is perplexing to you and you cant figure our how to figure it out

sell it

if it didn't throw a code immediately, it is likely NOT a HUGE issue

if you are venting metered air, it will run pig rich and if ya also have another leak closer to the tb...it can easily DO THAT

id bet it split the Y pipe under the intercooler
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Old 03-24-2015, 11:42 AM   #10
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Quote:
Originally Posted by Uncle Scotty View Post
and if this is perplexing to you and you cant figure our how to figure it out

sell it
(With all due respect) - can you explain what you mean by this? Surely you can't mean if anyone has a problem they can't fix or figure out themselves, sell the car. What would shops be good for then? The average person who has no idea about cars would be screwed.
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Old 03-24-2015, 01:01 PM   #11
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Quote:
Originally Posted by billyboy999 View Post
(With all due respect) - can you explain what you mean by this? Surely you can't mean if anyone has a problem they can't fix or figure out themselves, sell the car. What would shops be good for then? The average person who has no idea about cars would be screwed.
What he is saying is that if you can't figure out to check something as simple as that using your common sense A.) You shouldn't track the car. B.) You should sell it because these cars will require a bunch of knowledge and know how to maintain them especially if you push them to the limit like you did on the track.
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Old 03-24-2015, 01:13 PM   #12
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Sounds like a leak. "stuck valves" typically make a bit of a racket...

easiest way to see if you're leaking metered air is to unplug the maf sensor and see if it runs better...
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Old 03-24-2015, 03:19 PM   #13
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It's been said a few times, but the symptoms point to a hose/coupler off of the pressure side of the turbo.
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Old 03-24-2015, 07:59 PM   #14
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Quote:
Originally Posted by billyboy999 View Post
(With all due respect) - can you explain what you mean by this? Surely you can't mean if anyone has a problem they can't fix or figure out themselves, sell the car. What would shops be good for then? The average person who has no idea about cars would be screwed.

the average person shouldn't be ****ing around with 'tracking' any Subaru....

you NEED to sell the car.

if you cant figure out how to diagnose, troubleshoot and make simple repairs to your Subaru, you shouldn't own one unless you have thousands and thousands of dollars to dump STRAIGHT down the toilet, and I mean that in a very literal sense

and if you DO have that kind of money, you are an idiot for buying a Subaru in the first place
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Old 03-24-2015, 08:05 PM   #15
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i love this place
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Old 03-24-2015, 08:11 PM   #16
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I love Uncle Scotty
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Old 03-25-2015, 03:36 PM   #17
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Lol!!!!
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Old 03-25-2015, 03:45 PM   #18
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I love Uncle Scotty
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Old 04-04-2015, 08:16 PM   #19
billyboy999
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So the car is fixed. GST Motorsports in the Bay Area did a great job.

The issue was a broken spark plug. It's not what you're thinking though - the part that connects to the coil pack was broken somehow. It was loose and firing maybe 20% of the time.

I should have seen a misfire or roughness code of some sort. When the mechanic drove my car, roughness on cyl 4 was through the roof. However, the mechanic said the tune on my car was suppressing it for some reason.

The mechanic then called me to approve a compression/leakdown because he was "99.9%" sure it was major ringland failure. The additional thing that got him thinking that was the fact that there was smoke coming out the oil filler. Then he got the sparkplug out and it was pretty obvious that the plug was the problem. All 4 plugs were replaced to be safe. Cyl. 4's leakdown was 4% - excellent.

Failure to build boost - when I reset my ECU to try see if that would fix the problem, I forgot to reflash from the default map which has no boost. So facepalm for me there.

There was an additional issue complicating the matter: I was supposed to drive back up to Seattle the following day. Meaning I couldn't take my time debugging the issue myself. If it was a boost leak, could I have debugged it myself? Probably; I've taken the intercooler off before. But there was literally no time to do that. Given the information I had at the time, I made the decision to leave the car in California to have a shop fix it, and hitched a ride back up with a friend.

Uncle Scotty, I agree with you, but this wasn't a simple issue and the circumstances meant I had to take it to the shop anyways.


So, in my defense:
0. I'm no pro, but I'm not the 'average' person either. I do my own oil/brakes/minor maintenance. It goes to the shop if it's something serious or I don't feel like fixing it myself.
1. No misfire/roughness code. This is the big WTF. I plan on calling up my tuner and asking him what is up with that.
2. Given the cyl 4 roughness information, the mechanic was still mystified. He made it clear over the phone it was the first time he had seen something like this.
3. I didn't have any time to debug the issue.
4. No one in here suggested a spark plug issue so...


Anyways, thanks (or no thanks?) for the help, hopefully this was entertaining and/or interesting.
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Old 04-05-2015, 10:49 AM   #20
billyboy999
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Also, I didn't mention this, but I WAS trying to debug the issue on the way back from the track. The reason I dismissed the possibility of a boost leak was that for a given boost level (for ex. 0 PSI @ 3K RPM), the injector duty cycles looked normal (20%). IDC is something I always have up on my AP so I'm familiar with what's normal for any boost level. If I understand how our cars work, if there's metered air leaking, the IDC would be much higher for a given boost level. Timing was normal too. At that point I'd gotten home so that was it for debugging; there was nothing more I could do but speculate.

Since boost and IDC were good, the car wasn't technically 'rich', but practically speaking, it was, and it wasn't making the power for a given boost level (you can have all the boost leaks you want, but at the end of the day, manifold pressure is final). No misfire code, so I assumed the spark plug was working. My next thought was something that massively affected compression. Valve, ringland, etc.
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