[Conekiller13]

I was hoping for some support with an issue I have been having with My '05 STi. The car is virtually stock with a K&N Typhoon intake. The car has 58k and the K&N has been on there since around 30K. The problem started a few months ago when my hood scoop ejected itself on the freeway. As near as I can tell the four nuts on the front side must not have been properly tightened at the factory as the studs were not broken when I picked up the scoop but all the nuts were gone in front. Anyway, while I was waiting for a replacement I removed the inner scoop structure because frankly it looked ugly and driving around with a hole in the hood was less ugly. About 15 miles into the first drive with a hole in the hood the check engine light came on while cruising down the freeway. I took the car back to work and interfaced it and found PO301 thru PO304 codes. No random misfires though. Freeze frame data was inconclusive just verifying closed loop and minimal engine load. I cleared the codes and reinstalled the inner portion of the scoop. I drove around that way for about a week no issues. When the outer portion of the scoop came in I installed that and once again the check engine light came on under cruise on the freeway. I interfaced again and found the same codes and same basic freeze frame data. I don't have a factory Subaru scan tool so all I can pull is OBD II global info, I cant read live data for fuel trim and such. None of My techs had any real good idea so I took it to a dealer to get diagnosed. Their first go round was that the K&N filter had gotten the MAF dirty. They said they cleaned it and all's well. So I pick it up and on the way home the light comes back, same codes same freeze frame data. I go back they say it needs a new MAF. I install a reman unit and clear codes and codes come back under same conditions and same freeze frame data. Subaru then say the reman unit doesn't read properly and it must be a O.E. Unit. I install an O.E. unit, clear codes and drive. Light and codes and same freeze data come back under same conditions. The tech at Subaru says the fuel trim is going all over and that the K&N is bringing in more air the the MAF can deal with. When I asked if that is the case how could it have gone almost 30k miles with out issue he didn't really answer.

Logic tells Me that if the original MAF sensor was in fact bad the would be some change in the symptoms and the data if only minute with a new one installed. I would expect if the reman MAF I put on was truly bad I would have gotten a MAF related code or a different symptom. Subaru wants me to go back to the stock intake with the new MAF and "see what happens". They also "suggest" that I replace the Air/Fuel (front O2) sensor. Since I'm out $100 in diag time to them and $170 for a MAF with no change I'm a little leery throwing more parts at it to see what happens. This misfire happens only on the second freeway drive cycle at a constant 3k rpm with minimal engine load and the boost gauge at the bottom of it's register. Just before the MIL comes on you can feel the surging. I figured it was a lean miss but the Subaru tech said most of the data He was seeing says running rich especially at idle. The rich running is why He wants the O2 sensor replaced.

I hope there is some help available.

[CGMDan]

Bump so I don't have to keep hearing him whine about it.!

[will12345]

i would say bad coils but that would be too easy lol

[Conekiller13]

I wouldn't expect bad coils to effect all four cylinders.........or that they would fail this early, that goes for plugs to. I figure it has to be something air intake related but what?

[Conekiller13]

Should this be under Engine, power and performance?

[Conekiller13]

Obviously no one here has any idea...................anyway, put the O.E. airbox back on so car is now back to stock. No change in symptoms or codes.

[Conekiller13]

Bueller?............Bueller?..............Bueller? ..................


Crickets chirping in the distance...................

[VanishingPoint]

Do you figure its related to the scoop failure?
Could there be damage caused to the TMIC.
A rich mis would cause black smoke and fouled spark plugs causing a no start.

I would check the plugs and check them to see how its running (a/F) While they are out check the compression.

Fuel trims all over could be an intake leak some where.

Im with you sounds like a lean mis. The O2 shouldnt be able to control to a lean mis, but a MAF/intake problem could.

You may want to check for a leak caused by something damaged from a scoop malfunction. Thats when it started right?

Tony

[Conekiller13]

Originally Posted by VanishingPoint

Do you figure its related to the scoop failure?
Could there be damage caused to the TMIC.
A rich mis would cause black smoke and fouled spark plugs causing a no start.

I would check the plugs and check them to see how its running (a/F) While they are out check the compression.

Fuel trims all over could be an intake leak some where.

I'm with you sounds like a lean miss. The O2 shouldn't be able to control to a lean miss, but a MAF/intake problem could.

You may want to check for a leak caused by something damaged from a scoop malfunction. That's when it started right?

Tony

Thanks for the reply Tony.......

I've inspected tmic thouroghly and can not see anything other then the usual tweeked fins from everyday driving. I've searched for visible evidence of leaks or split hoses to no avail. The only thing I havent done is smoke test the intake system for leaks. I would have assumed the dealer tech would have done that during the diagnosis I paid for but who knows. I really think that is whatit will end up being though.
I t did start when the scoop came off but I just dont see how it could be related when there is no physical connection to the intake from the scoop. I would also think that if the engine was damaged because of super heated intake air beacuse the scoop was off it would not have done the exact same thing to all four cylinders. If it detonated and damaged pistions what is the likly hood that all four would be hit together? I think very slim and wouldnt a problem like that be much more symptomatic? Smoking, power loss and the like?

The car is back at the dealer again today (fourth time now) so I guess We'll see what thier next gues is.

[VanishingPoint]

Im curious what they find.
The intake system can be pressure checked I think there is a write up in the how to section (I think )
Good luck and let us know how it goes.

Tony

[Conekiller13]

Just got a call from the dealer............so now they say they have found a slight split in the air intake tube at the turbo causing un-metered air to enter the system thus causing a lean misfire. So.......they have now settled that it is in fact a lean miss.........before they were saying it was too rich (blaming the Typhoon and MAF). I figured it was a lean miss all along. Anyway, the only part of this guess that doesn't jive with My symptoms is that they say as it flexes under load it draws in air. The code is always set at cruise conditions at around 7% engine load at a steady 3000 RPM. When a drive hard (like the autocross this last weekend) I get no hiccups or CEL illumination at all.

At least I have a long weekend to pull it apart and see.......dealer quote for repair, about $650. My cost $100 in parts and weekend of time. So tune in next week campers to see if they were right this time!

[VanishingPoint]

What a dealer. By guess or by god they will figure it out.
$650 they should at least throw in a free hat. Subaru hat and not the dealer.
I usually get a kiss after a $#%*&%^ like that.

Waiting for results

Tony

[Conekiller13]

Well it would appear that the fourth time was the charm. After spending a good chunk of My memorial day weekend R&Ring the intake to get the turbo inlet tube out and the new one in (the old one had an oily residue and was very soft and tearing) it seems to be good. It is now back to the way it was with the K&N Typhoon and the original MAF sensor and has been on many drive cycles that before would have thrown the misfire. All seems good so far..............of course it occurred to Me only as I was reassembling that maybe I should have upgraded to a silicone inlet pipe...........oh well.

So all in all the dealer refunded My initial inspection charge since it was way off the mark and charged Me $180 to actually find the problem. Luckily I can return the two MAF sensors I purchased as well so total cost is just under $300 with the new inlet pipe and gaskets.

[johnlude85]

verry good!!! as i was reading this, i was thinking to myself "hes gonna get it, hes gonna get is" meaning youre going to figure it out. every time you posted you got closer to the cause of the problem lol. there should really be a TSB for this because a buddy of mine is a subaru tech and he says he has seen this problem more then a few times. and im sure more dealers have seen this too. they tend to split right before the turbo depending on the year. so im glad you figured it out because that was what i was going to suggest

[Conekiller13]

Originally Posted by johnlude85

verry good!!! as i was reading this, i was thinking to myself "hes gonna get it, hes gonna get is" meaning youre going to figure it out. every time you posted you got closer to the cause of the problem lol. there should really be a TSB for this because a buddy of mine is a subaru tech and he says he has seen this problem more then a few times. and im sure more dealers have seen this too. they tend to split right before the turbo depending on the year. so im glad you figured it out because that was what i was going to suggest

Yea, a TSB would have been very helpfull...........