Legacy GT-B e-tune intermittent misfire and hesitation under load

Discussion in 'Subaru' started by jsdub1, Nov 2, 2015.

  1. jsdub1

    jsdub1 Mister

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    I have had some hesitation since I got the car, always very minor, I didn't really notice it for quite a while but looking back it was there.

    Symptoms: when I start to apply 50-70% throttle, the car will start to accelerate, then stumble once or twice between 2500 and 4000 rpm, changeover happens, then I will get another one or two misfires / hesitation then the car will continue to accelerate as normal.

    This has really begun to get worse recently. Car was also limiting itself to 7psi and not changing over to twin mode, right around when the misfire was getting really noticeable. Sometimes when the car is idling, it will misfire randomly (i can feel a slight bump and I can hear the revs change). Sometimes I start the car and none of this happens at all, it's making it very hard to pin down.

    Mods / work done to the car: (Some may not be relevant but I will include it all)

    timing belt changed by a pro
    All new vac line throughout engine bay / BBOD
    New Coolant lines
    Block heater installed
    All fluids changed (coolant, tranny, diff, oil) confirmed proper levels
    silicone turbo -> intercooler piping
    silicone intercooler -> throttle body coupler
    beatrush forged pitchstop
    charcoal canister solenoid broke so I have removed this and capped the lines.
    blitz pod filter
    HKS axle back
    New NGK iridium plugs (BKR6E IX)

    Funny enough, this problem really started to show after the intercooler piping and charcoal canister solenoid delete so I am going to take another look at how I capped the line and make sure everything on intercooler is rock solid, what if it's a simple vacuum leak?!?

    What's the verdict on injector cleaner, does the stuff actually work? I think I'll run some through the system and see if it helps. I'm also going to clean all the ground connections I can find.

    Oh I did also try a different set of coil packs but the misfire was much much worse with those, but it could have been the plugs being incorrectly gapped as well, so I will swap those back in with my correctly gapped plugs and see if they change anything.

    If that doesn't work, I am thinking of replacing parts in the following order:

    1.) o2 sensor
    2.) coil packs
    3.) fuel filter
    4.) injectors

    Looking for opinions and experience, let me know if you had something similar happen and what fixed it! Please! ha. ha. -___-
     
  2. grayhamwiebe

    grayhamwiebe New Member

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    When you tried different coil packs, were the good ones? If it made it even worse I would guess not. Bad coil packs are always the first thing that comes to mind when a Subaru is misfiring. Especially if the problem is amplified under heavy throttle.
     
  3. jsdub1

    jsdub1 Mister

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    It did get worse with the new (they are used but came from another running GTB) coil packs but I also had the plugs gapped incorrectly. Next on my list is switch those coils back in now that the plugs are gapped correctly. Coils were also my first thought.
     
  4. mekazilla

    mekazilla Theoretician

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    Mine did this similar hesitation. I put a new maf in and that helped. Also did the coils, that helped. O2 sensor helped. 255 fuel pump helped.
    Everything helped but it still occasionally hesitated, usually when you would decelerate in gear and the get back on gas.
    When the weather got cold it hasn't hesitated for a while now.
     
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  5. jsdub1

    jsdub1 Mister

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    thanks for the reply. Yea, i've been looking everywhere and seems like there's a lot of different causes for the same problem. I've gotta just start with the cheapest/easiest and work my way down.
     
  6. jsdub1

    jsdub1 Mister

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    So I cleaned my ground wires last night, this helped quite a lot. Hesitation is now only present in secondary mode, it's quite a hard judder though. not a fuel cut, but pretty badly misfires. Still have the occasional misfire at idle and it's a little rough. Hoping it's coil packs. Will swap them in tonight and if it still does it then it's time for a compression test.
     
  7. jsdub1

    jsdub1 Mister

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    Well, compression test came out great, very consistent all around. like 145 psi after 6 cranks.
    Tried a known working MAF, it didn't change anything! Next up is knock sensor. I may pull the intake manifold while I am at it, I feel like it could be a cracked turbo inlet. Buddy pointed out there was a strange whistling sound while we were listening to the car last night.
     
  8. mekazilla

    mekazilla Theoretician

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    Yeah I did knock sensor as well. The stock one is a pain to take out. You can leave it in and just mount the new sensor to the block as close as possible.
     
  9. jsdub1

    jsdub1 Mister

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    I've seen a couple walkthroughs and it looks like a pain to get to. How did you mount it without taking the old one out? Do you have a picture?
     
  10. mekazilla

    mekazilla Theoretician

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    No picture sorry. It was just up and an inch or 2 away where one of the hardline brackets mounts to the block. You may need a longer bolt.
     
  11. Bushman

    Bushman New Member

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    Run a code check, connect two single wire connectors under the dash, drivers side left. There is a thread on it here I think how to read the flashing check engine light to determine code.
    I had same symptoms and it was a bad knock sensor and MAF which is common ..reset computer after new part.
     
  12. jsdub1

    jsdub1 Mister

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    Yea man, first thing I did, no codes yet. I've heard MAF death is pretty obvious, from a guy who's killed 2 of them. Plus we tried a good one and no change. ECU has been reset after everything. Guy who's familiar with these cars seems to think knock sensor is the culprit.. guy I know here drove his B4 for 2 months before it threw a code.. haven't had a check engine light yet, just runs like shit.
     
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  13. jsdub1

    jsdub1 Mister

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    Also checked the coolant system for airlock, I tried burping it again, didn't get any bubbles.
     
  14. jsdub1

    jsdub1 Mister

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    can not wait to try this fucknig knock sensor tonight. I am definitely leaning toward electronics becuase of how inconsistent it is.
     
  15. grayhamwiebe

    grayhamwiebe New Member

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    On my Wife's forester it was a bad knock sensor (the sensor was split in half), which is an easy and cheap job to fix on an NA Subaru. It had the check engine light go on and off while it was broken.
    I hope that solves your issue.
     
  16. jsdub1

    jsdub1 Mister

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    yessss it was the knock sensor. I swapped in another, which happened to be broken, but I finally got a cel with code 22. car isn't misfiring at idle and is much more drivable. my theory is, because my old sensor was so corroded and dirty and filled with crap, it was sending a bad signal. now with a truly shot sensor, the car doesn't get any signal realizes it's a problem.
     
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  17. magnavahn

    magnavahn Vahn

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    Late to the party. I had this problem on one of my old sti's. It was 50-90% throttle in 2-3-4 gears. New plugs (it preferred cheap coppers) and a knock sensor fixed the problem.
     
  18. jsdub1

    jsdub1 Mister

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    Shoot I spoke too soon. Car feels nicer everytime i swap in a new part. brand new knock sensor did not help, although the car ran great for a time after an ECU reset. The car actually runs great after each ecu resest, for a few kms. after I am all properly warmed up, it starts to shit the bed again. Maybe 02? I drove with the 02 unplugged and it didn't change a thing. I dunno if that means it's still good or gone bad.
     
  19. jsdub1

    jsdub1 Mister

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    Cheap? lol $180 for the sensor from subaru
     
  20. grayhamwiebe

    grayhamwiebe New Member

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    That's why I don't buy from dealerships for most things. I think I payed about $45 for mine brand new from an aftermarket company.