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Old 03-07-2014, 06:26 PM   #1
Blingstrom
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Default compression close but not good enough?

05 sti Cobb stage 2. 93k miles. Plugs less than 5k old and gapped properly.

Cylinder 1-3:145
Cylinder 4:130

Having issues with rough idle with roughness count goes to 14 when idling for 3 mins wanted up. Car runs hard and smooth through the power band.

No smoke or hard starting... Less than 1/2qt at oil consumed in 2k miles. Coils and plugs have been switched with no change.

Cel has came on around 4 or 5 times in the last four months for just cylinder 4 misfire.

Only other noteworthy issue is when in second gear in open loop if I go from 2k rpms to 3k it will chug. Doesn't do it any other time but the first time after being started and in 2nd gear and it has done this for about a year+ and always thought it was something it just did with the Cobb tune.

I have been searching for a couple months for answers but haven't found anything else with a similar problem/answer. Want to do a leak down just haven't had a chance to rent one or borrow. Thanks for reading.
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Old 03-07-2014, 06:49 PM   #2
AlexWRXbruh
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Sounds like cylinder 4 is big problem for everyone..maybe your ring gap is widening a lil bit, no need for alarm..eventually it'll **** the bed n you'll know it
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Old 03-07-2014, 07:09 PM   #3
Blingstrom
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Yeah have read a lot about it. Was thinking of replacing the fuel pump or offending injector but don't want to just throw parts at it. Engine rebuild money is safely acquired so that isn't a big deal.

Just hopeful someone had a similar issue and would easily identify. Really didn't want post another cylinder four misfire post but just couldnt find the info to help.
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Old 03-07-2014, 09:00 PM   #4
Andrewxxcarlson
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Interested, similar ongoing issue
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Old 03-07-2014, 09:32 PM   #5
IGW
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You should have around 8 psi or less difference between cyl
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Old 03-08-2014, 10:09 AM   #6
Blingstrom
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I think 7-10% is often the goal... Best to be closer but this lands me right outside of it.
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Old 03-08-2014, 01:56 PM   #7
boosted25
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Honestly I wouldn't worry about it. Check it again in a few months and make sure it hasn't lowered anymore in that cylinder. Also keep an eye on your vacuum gauge during decel and idle and watch for less vacuum being pulled over time.
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Old 03-08-2014, 10:31 PM   #8
Blingstrom
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I do keep an eye on idle vacuum and it moves ever so slightly when the engine misfires enough to feel the car shake.

I will have to check it out during decel and see if is doing else odd. Thanks for the advice.
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Old 03-10-2014, 11:08 PM   #9
Blingstrom
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Spring is here and temps rose to 75. Checking on my ap during a 35 mile drive it knocked 1 roughness in cylinder 4. Idle was back to normal with no issues. Is this odd?

Is there a sensor that can be throwing off just that cylinder when temps are below 40? Any help would be much appreciated.
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Old 03-11-2014, 08:37 PM   #10
Mefistofer
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My compression values are just like yours, and mine has rough idle as well, I am looking into some information about an ECU recall, mine is a 2007 though. A friend of mine told me it would be worth trying to clean the throttle body as the throttle stepper motor is very sensitive... Mine is throttle by wire
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Old 03-28-2014, 05:33 PM   #11
Blingstrom
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Just wanted to update this for anyone else checking or reading. Ended up swapping injector 2 and 4 and the misfire had moved on to 2. It seems less intense than before but still shows up on the Ap.

Hope this helps anyone else out there.
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