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Old 01-23-2008, 03:04 PM   #1
07stilover
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Default 07 STI Blown Piston or Ring?

2007 sti and I have a catless tbe with aps 65mm cai running on cobb stage 2 map. I recently went to a tuner to get a protune and he wouldn't touch my car because he said i probably blew a piston or ring. I don't have any smoke (blue or white) and my engine doesn't feel any different. My idle after warm up is around 690-750 rpm. He claimed there was something wrong with the idle. Do you guys think i have a problem? How can i tell if i need a comp test? I don't want to spend 200 bucks for a compression test if i don't have to. Thanks.
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Old 01-23-2008, 03:12 PM   #2
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We have no way of knowing if you have any damage.

You need to do a compression test. Leakdown would be better because sometimes blown pistons hold enough to pass a compression test.


FYI you can have a very badly blown cyl and it doesnt always feel any different or make enough of a difference in power that you can really even feel. If you are having idle problems from a blown cyl it will usually manifest itself in a stumble not just low idle.

However you should have your car looked at if you are idling that low. You should be about 100-150rpm higher than that I think. I dont see a blown piston making you have a smooth but slightly lower idle, it could be any number of things causing it. Or it could be a lost cyl. There really is no way to know for sure without doing a compressor or leakdown test.


Be ready because its highly likely a lot of people are going to come in here and blame the intake. The APS 65mm intake doesnt cause problems and cobbs map works fine on it just like theirs. Cobb only recommends their intake because that is the one they have tested and can give backing to saying it works well.
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Old 01-23-2008, 03:20 PM   #3
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What's your idle vacuum?
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Old 01-23-2008, 03:22 PM   #4
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catless tbe + intake on OTS map... how many miles have you had those mods?
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Old 01-23-2008, 03:29 PM   #5
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get tested, and not at the clinic..
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Old 01-23-2008, 03:29 PM   #6
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Wow, my idle at warm up is 500rpms, and my car is mostly stock (SPT intake and SPT catback).
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Old 01-23-2008, 03:33 PM   #7
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if you can change a spark plug you can do a comp test yourself. You can either buy the compression test kit at an auto parts store or I think autozone lends out specialty tools for a small fee.

Then again if you dont feel comfortable doing it yourself pay someone
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Old 01-23-2008, 03:58 PM   #8
07stilover
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Thanks for the replies guys. How do i check for idle vacuum? I've had the catless tbe on cobb stage 2 map for about 9 months and the aps 65mm cai for half that time.

Maybe with the recent cold weather, the cai is causing my idle to fluctuate abnormally? The car feels fine and it only has about 7700 miles and i don't beat on it. Only during this past summer i beat on it a little bit on a saturday night. I had zero problems. I always do the oil change myself and i know i'm not losing oil.
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Old 01-23-2008, 05:06 PM   #9
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AFAIK 750ish is ok, my car drops to low 700 rpms when the radiator fan kicks in.... What else is wrong with ur car?????
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Old 01-23-2008, 05:13 PM   #10
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Quote:
Originally Posted by scrapiron7 View Post
Wow, my idle at warm up is 500rpms...
wanna bet?


OP, if you have an AccessPort, use the live boost feature to check your idle vac. You had enough money for a Pro-tune but not enough for a compression/leakdown test? You may need to re-think your priorities.
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Old 01-23-2008, 05:25 PM   #11
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^^^^uh???
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Old 01-23-2008, 05:37 PM   #12
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I idle around 550-650 in all 4 WRXs I have owned or currently do (02 WRX, 06 WRX, 06 STI (current, my wife Tess's car), 07 STI (current)). With the AC on of course the idle moves around.

But yeah there is only onw way a tuner can suspect an engine problem via ECU. You monitor cylinder roughness. If it is not within spec, then the dealer will do a comp check and leakdown.

More than likely the tuner sent you away because he checked that first (I usually do this as well).

Gabe
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Old 01-23-2008, 05:38 PM   #13
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definatly do a leak down, my idle is normal and I have cracked ringlands, but I am burning a crap load of oil you wanna look back on decel thats when you'll see blue smoke
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Old 01-23-2008, 05:48 PM   #14
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How do yyou check/interpret a cilinder roughness, I though comp/leak down test was the only way to check
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Old 01-23-2008, 05:50 PM   #15
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the confusion with some of the posters here is that the line that the tach needle sits on at idle is commonly thought to represent 500 but it actually represents 750 rpm.

as for as the OP... hopefully the shop can provide you with more info but it never hurts to do a comp test anyway. like said above, if you can change your plugs, you can do a comp test.
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Old 01-23-2008, 06:14 PM   #16
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Quote:
Originally Posted by Wrinkleboi View Post
the confusion with some of the posters here is that the line that the tach needle sits on at idle is commonly thought to represent 500 but it actually represents 750 rpm.

as for as the OP... hopefully the shop can provide you with more info but it never hurts to do a comp test anyway. like said above, if you can change your plugs, you can do a comp test.
i havent counted the lines on my stock tack yet but i always thought i saw it at 550-600rpms at idle.
are u saying the stock tach is off or the tach lines are drawn on wrong?

Last edited by Chris85xlt; 01-23-2008 at 06:19 PM.
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Old 01-23-2008, 06:39 PM   #17
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idle should be at 750-800 rpms
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Old 01-23-2008, 06:48 PM   #18
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Your tuner turned you away because of the way your car was idling? Thats odd. If he didn't even hook up to the ECU and monitor anything then he himself doesn't know if theres an issue.

I have a APS DR525 FMIC, APS65mm CAI, Walboro 255 Fuel pump, 3" TBE on a Cobb Stg2 OTS map and my car is fine.

What is your car doing? Does the idle jump up and down at times? This is most likely because of the intake and the ECU not being tuned just right for the amount of air its receiving. When it gets the gusts of air into the intake it will release more fuel to compensate which results in a rough idle or a "jumpy" idle.

My bets are that you are fine. If there is more to the story then please let us know for your sake.

If your THAT worried about it, bring it to the nearest shop for a comp. test. It's not that much.

Ryan
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Old 01-23-2008, 06:54 PM   #19
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im surprised no one mentioned this. you are not supposed to have a catless exhaust on an 07 sti with cobb mapping. not that its what the tuner found problem is, but regardless i thought id mention it.
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Old 01-23-2008, 07:30 PM   #20
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Quote:
Originally Posted by b0nd18t View Post
im surprised no one mentioned this. you are not supposed to have a catless exhaust on an 07 sti with cobb mapping. not that its what the tuner found problem is, but regardless i thought id mention it.
I was just gonna mention this. Cobb says all over their products and website to only run a catted DP with their OTS maps. If you want a catless one get it tuned simple enough.

If you're willing to spend $700 on the AP and anywhere between $800-$1200 on a TBE (depending on the brand parts) you should be able to pay for a $200-$300 tune. If not, don't by the AP and the exhaust. Thats the way I look at it, sorry if I'm offending anyone.
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Old 01-23-2008, 07:52 PM   #21
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cobb blah blah blah, the only reason they say no catless TBE is because of overboosting, your more prone to the overboosting when its cold out. If the car is tuned properly with a catless TBE you shouldn't be over boosting.
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Old 01-23-2008, 08:16 PM   #22
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Quote:
Originally Posted by ronzogonzo View Post
cobb blah blah blah, the only reason they say no catless TBE is because of overboosting, your more prone to the overboosting when its cold out. If the car is tuned properly with a catless TBE you shouldn't be over boosting.
Yes this is 100% true and I agree but the thing is Cobb's OTS maps are NOT tuned for catless and as a result not tuned to control as much over boost as what is possible with a catless setup.

The OP said he was using the stage 2 OTS map. And it's an 07 STI we all know that protune is the only way.
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Old 01-23-2008, 08:25 PM   #23
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Quote:
Originally Posted by 07stilover View Post
...How do i check for idle vacuum?
Start it up warm, let it idle, plug in your AP and go the live boost feature - what's the number?

The bottom line is if you've blown a jug, you'll normally get a large drop in idle vacuum, plus you'll blow smoke and pressure out the oil filler tube when you rev it. Compression/leakdown is positive proof, but you almost always have both of these symptoms too and I'm really surprised your tuner didn't check these.
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Old 01-23-2008, 08:50 PM   #24
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So what should vaccuum at idle be? I see -20 to 25 in HG (according to my Defi gauge) on my 07 STi, running Cobb stage 2 with a catless exhaust, and an APS 65mm intake (for the last few hundred miles).

I think the whole blown 07 motor thing is a little blown out of proportions. How many toasted 07 motors have there been, a dozen, tops? Sure, that sucks, but out of thousands of 07 STi's? Still not a overwhelmingly likely as people make it out to be, I think. I've been running like this (minus the APS intake) since ~4k miles or less (at ~12.3 now). Hell, I don't have ANY oil consumption. The most I've ever added was a fraction of a quart before a long road trip, just to be over-cautious.

Last edited by KevlarSTi; 01-23-2008 at 08:55 PM.
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Old 01-23-2008, 09:07 PM   #25
flycaster
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Quote:
Originally Posted by KevlarSTi View Post
So what should vaccuum at idle be?
20-22 inmg, stock motor, at sea-level - it falls off with altitude. If you normally see 20, and all of sudden it starts to run rough and you only see 15, it's time to start investigating. If you then pull the oil filler cap off, and get oily smoke at 2K rpm, it's time to get out the wallet. And if you don't, count your blessings and start looking for the vac leak.
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