'07 STi Cylinder 4 misfire

cameronb96

New member
Car is at 113k miles and timing belt and water pump have not been done quite yet.
 
Here are the symptoms:
 
-Occasionally under heavy throttle the car will stutter instead of accelerate, anywhere from 2500 to 3500 RPM.  This only seems to happen in 3rd gear and up.
-This could be linked to the previous, but in 6th gear at around 60mph when I can hear the turbo spooling under throttle, it also stutters and I can hear it in the whistling noise, and boost wont build up.
-Code P0304 for cylinder 4 misfire
-Oil is normal color and texture, tested before and after an oil change and letting it run for a bit
-Exhaust smoke is not discolored
-Only seems to misfire when idling, possibly more in reverse I've noticed.  It also happens very rarely, even where I've driven it a lot since it first started happening
-Car is slow/weak to start(like a weak battery), but the battery is the same as from the factory so I will be replacing that soon.
-When driving while viewing the boost gauge on my AP, the boost does not want to go above roughly 7 psi a lot of the time.
 
I did run a tank through the car with sea foam to clean the fuel injectors.
I also tested the spark plug(swapping with other cylinder) and coil pack and it still misfired on Cylinder 4.
 
If I remember any more helpful details later I will add them but thank you very much for taking time to read this and help me out.
 

drvsdwz

DRiVe SiDeWayZ
Sounds like a case of the ringlands...does it seem to skip while starting it? Do a compression test, then a leak down if you find compression down on 4.could be as simple as a fouled plug, or coil pack. Could also have skipped timing.

Timing belt should have been done 20k ago

That would pretty much eliminate jumped timing.

 

RyanR

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Could also be a lazy injector. Compression and leakdown tests should be performed before you spend time on anything else. May also be worth popping the timing belt covers off and checking to see if it's still timed.

do not drive it or start it until you validate that timing is still ok.

 

cameronb96

New member
Alright thanks for both of the replies.  Do the timing belts in the STi have a shorter life on average than another 2.5, or what's the earliest you've seen one cause problems?  

 

IBratmanI

Subaru Ambassador- AdidaSubarus
Alright thanks for both of the replies.  Do the timing belts in the STi have a shorter life on average than another 2.5, or what's the earliest you've seen one cause problems?  
They're supposed to be changed at 105k mile intervals.

 

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