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Hello all, you may all already know this but...

Just had my 2008 STI in for a new engine after 8K miles. The car was run in properly by bedding in the pistons rings by accelerating/engine braking for the first 50 miles, then oil & filter change, then keeping the revs mostly under 4K for the first 1000 miles (another oil & filter change) then normal driving until another oil & filter change at 5K. All on the recommended (in the UK) Fuchs fully synthetic.

An 'off duty' Subaru mechanic noticed a compression issue/particular noise when I started it at a Surrey Subaru Owners Club meet (the car was running fine but was burning a bit more oil than normal). A compression test revealed low compression on Number 4 piston (about half the compression of the other 3). I caught it just in time before it went bang...

When I rang Subaru UK to discuss the issue/warranty, before I even told them what piston it was, they said 'it will be number 4 then'. This is a common problem over in the UK!

Other than the poor quality cast pistons they put in the US/UK 2.5 STI (they put forged ones in the JDM 2.0 STI) it turns out there is a knock/det problem with the standard map from the factory. The ecu has thresholds for knock detection. They were set too low in the standard map from the factory and the car is able to pull higher load than the threshold, so the ecu is hearing the det but doing nothing about it...It is not specifically related to the boost level safe to run on the engine but the fact that the ecu is not monitoring engine noise and altering the timing...the end result is that it cracks the pistons due to det at high revs/near or on the rev limiter, and mostly on number 4 as this piston is prone to running hotter than the others (due to the oil feed that looks after this piston).

My new engine came with a new ecu map that retards the revs by 100rpm and deals with the knock/det issue, supplied by the factory/Subaru UK, to prevent this from happening again.

Subaru UK have not issued a re-call to have all 2008 STI's re-mapped but UK Subaru garages are re-mapping/flashing the ECU on all MY08 STI's when they come in for a service. In the UK this is done for free. If you have a MY08 STI I recommend you get on the phone to your Subaru Dealer and get them to flash your ECU as soon as possible, they should do it for free.

Alternatively if you get your car re-mapped by a specialist (EcuTek), any good mapper will ensure there is not a knock/det issue.

I thought American Subaru owners should know about this.
 

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Thanks for the info. This issue was addressed stateside sometime ago with a Subaru service recall. I had to bring my car in for it. I had already been AP tuned however knowing most Subaru OEM tuning issues :)

Also the break-in oil is supposed to remain for a minimum of 1k miles. Subaru actually recommends leaving it in for 3k for complete internal component seating. This break-in oil is actually of a special formulation with higher friction to allow the seating process to be thorough. Running a different oil early with less friction will not allow this to happen, especially if Synthetic was run before 3k.

Glad to hear they replaced your engine and you are good to go. :)
 

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Nope, out of the box, the WRX tune was safe.
 

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Actually you might be surprised to know that there are a LOT of 07/08 sti's running around with cracked ringlands and have no clue about it. It's overly overly common to find hairline cracks in the ringland on even "healthy" feeling motors. The only thing you can really do is compression checks and monitor oil consumption.

Also not sure subaru has ever put forged pistons in any version motor here or JDM. Its a commonly distributed myth.

SIDE NOTE: How the hell did you get to the driver's side (USDM) coil packs?? I'd like to do a compression checkup myself but isnt there a bunch of plastic tubing in the way??
 

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Thanks for the info. This issue was addressed stateside sometime ago with a Subaru service recall. I had to bring my car in for it. I had already been AP tuned however knowing most Subaru OEM tuning issues :)

Also the break-in oil is supposed to remain for a minimum of 1k miles. Subaru actually recommends leaving it in for 3k for complete internal component seating. This break-in oil is actually of a special formulation with higher friction to allow the seating process to be thorough. Running a different oil early with less friction will not allow this to happen, especially if Synthetic was run before 3k.

Glad to hear they replaced your engine and you are good to go. :)
Whoops ........ I changed out my oil at 500 miles.
 

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Exactly the same problem here... Piston number 4 has hardly any compression in it.. I did also notice when you start the car up theres quite a bit of misty blue smoke probably oil from what you have said becuase of said problem.

My car went in at 3k to have it's oil changed from the run in oil but the problem was happening since then but the garage didnt have a clue what was wrong with it as at first it seemed to fix itself and all of a sudden there be power again but as the clock got on another 200miles it started to get worse so it went in again today.

Thanks for posting :)
 

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Nope, out of the box, the WRX tune was safe.
Cobb stage 2 safe as well? I've had it dyno'd and the sheets reported a good if not a little to rich AFR. I would LOVE to run a little leaner (goes unreadable into the rich side when i WOP, or at least on the 4th gear pull).
 

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Nope, out of the box, the WRX tune was safe.
Cobb stage 2 safe as well? I've had it dyno'd and the sheets reported a good if not a little to rich AFR. I would LOVE to run a little leaner (goes unreadable into the rich side when i WOP, or at least on the 4th gear pull).
AP tune is cool as they fix the issues with the OEM tune running lean at the low end and also fix the error on this particular recall where at WOT @ near the red-line, the car runs lean.

CYL 4 is problematic due to its location against the fuel delivery and this cylinder needs particular attention in keeping it as cool as possible by letting it run a bit more fuel than the others.

How rich are you at stage 2 should be in the 11 range at WOT inder boost conditions
 

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Nope, out of the box, the WRX tune was safe.
Cobb stage 2 safe as well? I've had it dyno'd and the sheets reported a good if not a little to rich AFR. I would LOVE to run a little leaner (goes unreadable into the rich side when i WOP, or at least on the 4th gear pull).
AP tune is cool as they fix the issues with the OEM tune running lean at the low end and also fix the error on this particular recall where at WOT @ near the red-line, the car runs lean.

CYL 4 is problematic due to its location against the fuel delivery and this cylinder needs particular attention in keeping it as cool as possible by letting it run a bit more fuel than the others.

How rich are you at stage 2 should be in the 11 range at WOT inder boost conditions
My ap unit says it 11 at WOT, but on the dyno it says it goes as rich as 9.5
 

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Nope, out of the box, the WRX tune was safe.
Cobb stage 2 safe as well? I've had it dyno'd and the sheets reported a good if not a little to rich AFR. I would LOVE to run a little leaner (goes unreadable into the rich side when i WOP, or at least on the 4th gear pull).
AP tune is cool as they fix the issues with the OEM tune running lean at the low end and also fix the error on this particular recall where at WOT @ near the red-line, the car runs lean.

CYL 4 is problematic due to its location against the fuel delivery and this cylinder needs particular attention in keeping it as cool as possible by letting it run a bit more fuel than the others.

How rich are you at stage 2 should be in the 11 range at WOT inder boost conditions
My ap unit says it 11 at WOT, but on the dyno it says it goes as rich as 9.5
Min value is ok how is the average?
 

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Nope, out of the box, the WRX tune was safe.
Cobb stage 2 safe as well? I've had it dyno'd and the sheets reported a good if not a little to rich AFR. I would LOVE to run a little leaner (goes unreadable into the rich side when i WOP, or at least on the 4th gear pull).
AP tune is cool as they fix the issues with the OEM tune running lean at the low end and also fix the error on this particular recall where at WOT @ near the red-line, the car runs lean.

CYL 4 is problematic due to its location against the fuel delivery and this cylinder needs particular attention in keeping it as cool as possible by letting it run a bit more fuel than the others.

How rich are you at stage 2 should be in the 11 range at WOT inder boost conditions
My ap unit says it 11 at WOT, but on the dyno it says it goes as rich as 9.5
Min value is ok how is the average?
It ranges from 12 to 14.5 ad idle i think. Ill have to double check it.
 

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I think you're ok.
Do a datalog with the Accessport
14s on idle are ok
Should be in the 20s or so in between shifts
Average under boost in the 10s - 11s depending on conditions.
 

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I think you're ok.
Do a datalog with the Accessport
14s on idle are ok
Should be in the 20s or so in between shifts
Average under boost in the 10s - 11s depending on conditions.
Yeah, when I went and got my car dyno'd my A/F didnt go below 12 when I've seen it on my AP as low as 10. I really think they screwed up my pulls because it didnt seem like they went wideopen at anytime, low numbers, and the A/F just made me agree with my thoughts.
 

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I think you're ok.
Do a datalog with the Accessport
14s on idle are ok
Should be in the 20s or so in between shifts
Average under boost in the 10s - 11s depending on conditions.
Yeah, when I went and got my car dyno'd my A/F didnt go below 12 when I've seen it on my AP as low as 10. I really think they screwed up my pulls because it didnt seem like they went wideopen at anytime, low numbers, and the A/F just made me agree with my thoughts.
That sux what peak numbers did you pull out?
It should definitely go below 12, staged targets should be in the 10s if conservative 11s if you want more power 12 is kinds like asking for trouble if it isn't a race prep car.
 

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I think you're ok.
Do a datalog with the Accessport
14s on idle are ok
Should be in the 20s or so in between shifts
Average under boost in the 10s - 11s depending on conditions.
Yeah, when I went and got my car dyno'd my A/F didnt go below 12 when I've seen it on my AP as low as 10. I really think they screwed up my pulls because it didnt seem like they went wideopen at anytime, low numbers, and the A/F just made me agree with my thoughts.
That sux what peak numbers did you pull out?
It should definitely go below 12, staged targets should be in the 10s if conservative 11s if you want more power 12 is kinds like asking for trouble if it isn't a race prep car.
I had 250 whp 325 wtrq on dynojet. Dont remember the RPMs and cant find my dyno sheet, think I left it at work. There isnt a smooth line on it anywhere. From what my friend told me (He gets his EVO9 dyno'd all the time) they are supposed to calibrate the dyno for everycar. The guy here at the shop just drove my car around, straped it in and did my 5 pulls. Does what my friend said sound right?
 

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They do have to calibrate the dyno. But not for every car everytime unless they feel the need to do so since you are not doing it for tuning purposes but just to get a read. (Depends on mood or company policy) I would have to agree, with that mod list, it's pretty conservative but hey we can't judge from dyno numbers because dynos are different. What kind of gains did you get though? Weird if the lines are super rough also, especially from Perrin, they like smooth tapering boost and smooth power bands.
 

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They do have to calibrate the dyno. But not for every car everytime unless they feel the need to do so since you are not doing it for tuning purposes but just to get a read. (Depends on mood or company policy) I would have to agree, with that mod list, it's pretty conservative but hey we can't judge from dyno numbers because dynos are different. What kind of gains did you get though? Weird if the lines are super rough also, especially from Perrin, they like smooth tapering boost and smooth power bands.
As for gains, I'm not sure. I definitly felt the difference between the Cobb Stage 2 and the Perrin Stage 3. I was night and day!! I'm at work now so I'll look to see if I can find my sheet and take a pic of it to post but yeah it looks horrible with how jagged it looks. looks like a shark took a bite out of it haha.
 

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alright, I found my dyno sheet and took a quick snap of it with my phone. Keep in mind this is a 08 WRX not the STI
 

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