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Thread: misfire at low revs

  
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    misfire at low revs

    picked up my sri-t yesterday and it had a management light on, op-com showed up misfire faults. multiple cylinder mifire, cylinder 1 misfire, cylinder 2 misfire, cylinder 3 misfire, cylinder 4 misfire. also had a fuel trim fault logged but its got a new front o2 sensor fitted so wasnt sure if it was an old fault.

    I erased all the codes and it has driven a little funny since. its ok when it comes onto boost but under 2500 rpm its misfiring and im also hearing a little more induction roar from it. it has standard induction on it. i had a look under the car and it looks like it has a decat pipe on it. precat looks standard, could it be the decat thats causing the misfire or am i looking at plugs or coil pack?

    eml hasnt come back on since i erased the faults but i havent really driven the car any distance today, prob about 3 miles max. anyone come across a fault like this before?

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    I would guess plugs and/or coilpack would be the most likely culprit! But i'm not very mechanical so someone will have to confirm!

    Wouldn't imagine that a de-cat would cause misfire to be honest!
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    i didnt think the decat would do it but thought i would ask the question. my brother has a petrol saab 93 turbo, would i be able to rob his coil pack to try on mine or would it be different?

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    Not sure mate, couldn't tell ya personally!
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    Quote Originally Posted by Pllusy View Post
    i didnt think the decat would do it but thought i would ask the question. my brother has a petrol saab 93 turbo, would i be able to rob his coil pack to try on mine or would it be different?
    Saab has different lump in mate, check for oil down plug holes from leaking rocker cover gasket, check plugs, and then replace coilpack. do it in that order. as for o2 sensor, best to get in on a machine and check what the voltages are doing. if any are staying constant then the sensor is broken.

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    I had op-com on it last night, the front sensor is switching pretty quickly but the rear one doesnt seem to be doing much. i know from my nissan days that the rear sensor doesnt move very much, is this the same on the astra? ill whip the plugs out of the car later and have a look.

    im thinking that i would prob be as well replacing them anyway then its 1 less thing to worry about for a few thousand miles. should i put the ngk iridiums in it? as far as im aware the car is standard bar what looks like the decat.

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    Try the cossies. ebay special. i am running them with no problems as of yet. no hunting on idle either. Heard the iridium ngk's are bad for losing tips into the engine so i went with the cosworth plugs.

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    was goin to go pick a set up tomorrow hopefully so ill see what i can come up with.

    just been out in the car to go to the shops there. was really bad when i first started it up no power at all and really bad misfire. wouldnt go above 1800 rpm in gear and had alot of induction roar. dipped the clutch and gave it a rev and it took ages to build the revs up then once it went over 2000 rpm it was fine. drove it easy for a bit till it heated up and took it higher up the rev range.

    was ok once it came onto boost no misfire and plenty of power but when i let the revs drop down to 1500rpm it still had a slight misfire but was as bad as when it was first started up.

    eml never came on at any point which i found strange. symptoms are really sounding like ignition side of things breaking down. plugs and coil pack coming up i think.

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    as said dude let me know regarding the pack.

    send it up to the redline in 3rd. mine misfired like a bitch higher up the revs. about 5k upwards.

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    mine seems to be lower down its worse. then from 3k to 5k its fine. misfires slightly pretty much right through the rev range in 5th as well so that sounds similar to yours.

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