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Random Misfire!!!! HELP ME!!

This is a discussion on Random Misfire!!!! HELP ME!! within the General Help forums, part of the LSx Technical Help Section category; Ok got a 98 LS1 in my Camaro, ran like a top when I got it, 2 days after I ...

  1. #1
    Junior Member MonteSS454's Avatar
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    Random Misfire!!!! HELP ME!!

    Ok got a 98 LS1 in my Camaro, ran like a top when I got it, 2 days after I got it I scrapped my exhaust on a speedbump (Full length headers and 3in pipe) and the exhaust guy (Before I got the car) cut the exhaust to short and used a long sleeve clamp on it and long story short it seperated a bit from the headers. I could hear a decent leak in it and was gonna take it to my exhaust guy the next day, well I got up to the next stop light and I could hear and feel a miss, drove for awhile and got a hard code for cylinder 1, replaced the plug and it didn't fix it, got the exhaust welded up and it was still there. Me and a buddy swapped plugs, no fix, I did wires the next night, no fix. I found out it was cylinders 1 and 2 misfiring with my live data scanner, the others would miss once in a blue moon. Swapped some cols around, miss didn't move, swapped some injectors around, miss didn't move. Me and a buddy did a noid light test on the injectors, they were hitting just fine, did a spark test, sparking just fine. I checked the fuel pressure and changed the filter, solid ~60psi.

    Tried to rest the PCM, could never get it to, left the battery unhooked for an hour, no reset. Unplugged it for 10 mins, no reset. Pulled the 2 fuses for the pcm, no reset. Kinda makes me think faulty comp?

    We've narrowed it down to valves for bad comp and or crank sensor.

    We just did a seafoaming to the intake and could hear valve clatter after doing it, possible a broken spring but it only comes from the passanger side head, not the driver side but yet they are both missing.

    We are gonna do a leak down test and a compression test on cylinders 1 and 2 to see if we can come up with something.

    Car always throws the P0300 bastard code and won't just give us a hard code.

    I don't want to have to do any work to the heads because this is my daily driver and my back up is without a motor. I hate driving it with this miss because plugs are a PITA to change and I don't want to have to change them for awhile and I don't want any long term damage done.

    If someone has any other suggestions or any kinda input that would be great. Me and my buddy are both just scratching our heads with our thumbs up our asses and this one.

    Please LS1 gods help me fix this!!!!!!!!

  2. #2
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    98 have the perimeter bolts so taking the valve covers off is a pain in the ass but after your compression test I would take the valve covers off to check the springs to see if you do have one that is broke. Make sure all your rockers are tq to 22ft/lb. I used my in/lb wrench to do this, 264in/lb.

    good luck keep us posted.

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    Junior Member Butcher's Avatar
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    sounds like what was happing to mine... same codes #2 misfiring...

    Mine was a bad 02 sensor on the passenger side....

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    Now in Summit LT1 Flavor! Y2KArcticSS's Avatar
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    On the computer reset, did you have your key turned to the 'On' position when you unhooked the battery? Your computer won't reset (at least for a looong time) unless the key is on.


    And hello, fellow Okie

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    Junior Member MonteSS454's Avatar
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    Quote Originally Posted by Butcher View Post
    sounds like what was happing to mine... same codes #2 misfiring...

    Mine was a bad 02 sensor on the passenger side....
    No o2 codes except for no activity on the back banks due to no cats or o2 sensors.

    Quote Originally Posted by Y2KArcticSS View Post
    On the computer reset, did you have your key turned to the 'On' position when you unhooked the battery? Your computer won't reset (at least for a looong time) unless the key is on.


    And hello, fellow Okie
    I'll try that tonight and see if anything happens.

    Boomer Sooner

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    Now in Summit LT1 Flavor! Y2KArcticSS's Avatar
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    Quote Originally Posted by MonteSS454 View Post
    No o2 codes except for no activity on the back banks due to no cats or o2 sensors.



    I'll try that tonight and see if anything happens.

    Boomer Sooner




    Be sure and let us know when you come to a solution It could always help us other DD Camaros in the future (166k miles and counting)

    2016 Summit White 1SS - The DD
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    Junior Member MonteSS454's Avatar
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    Well if it comes down to be the heads and it's not a simple fix, I'm gonna spend about $2500, get LS6 heads, cam and intake.

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    Junior Member Butcher's Avatar
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    Quote Originally Posted by MonteSS454 View Post
    No o2 codes except for no activity on the back banks due to no cats or o2 sensors.
    Right but you have misfire codes... mine did not throw a 02 code either it threw po300 & po302 wich is a multiple misfire & misfire in #2 cyl, swap out that 02 sensor on the ps takes about 10mins, and pretty cheap to do, or switch sides w/ the 02s & see if you code moves to another cyl

    I just got done messing w/ this I was doing every thing you have talked about to try & figure out what was going on & it was that dam 02

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    My SS had a P0300 once. It was a loose #6 plug wire. Made all wee tight on plugs and coils. 2yrs and no more problems.
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    Junior Member MonteSS454's Avatar
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    Ran a compression test and had 120psi on each cylinder 1 and 2 so i dodged a bullet in the head there and while me and my buddy were thinking of it, with a dead miss the head would tick anyways, so we eliminated the heads and are to the crank sensor and or pcm, may o2 sensor?

    All my plug wires are tight both plug and coil side.

    Maybe i can get lucky unplug the o2 sensor and see if it clears? Has happened with a tps on one of my trucks before, one way to find out.

    But we're taking it to my buddies mechanic tomorrow to see what he says, its really throwing us both for a loop because he is an LS1 buff and I know enough about them to throw out some specs and blah blah blah......

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    Member foxman92's Avatar
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    i would say its either the 02 sensor's, or one of the knock sensor's, a buddy had the same thing happen to his t/a and it was a knock sensor..

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    Junior Member MonteSS454's Avatar
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    Ok my mechanic (27yrs of experience) has no idea what it is, he told me and my buddy to take off the valve covers and check for broken valve springs or a backed off nut on the rockers or something to give us a clue!!!!

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    Junior Member Butcher's Avatar
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    Quote Originally Posted by MonteSS454 View Post
    Ok my mechanic (27yrs of experience) has no idea what it is, he told me and my buddy to take off the valve covers and check for broken valve springs or a backed off nut on the rockers or something to give us a clue!!!!
    have fun w/ that, dude go buy a 02 sensor from napa 75 bucks, throw the car on a lift, unplug the ps 02 unscrew it from your exhaust, put in the new one, If it dont work clean it up & take it back, 15 mins of work a lot les BS then pulling valve covers....

    Or have your mechanic of 27years hook the thing up to a scanner & see what the left 02 & right 02 are doing As you can see fron this pic mine was just off .044 0f of the other....which makes the pcm think its still in a warm up mode & dumps fuel into the ps bank of cyl causing your misfire....

    Last edited by Butcher; 07-22-2009 at 04:25 PM.

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    Junior Member Butcher's Avatar
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    So how did the valve cover pull treat ya??? did ya find anything wrong???

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    Junior Member MonteSS454's Avatar
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    Pulling it tonight, hoping for the best. Gotta rig up the wiring to swap 02 sensors because of my headers, am doing that soon.

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    Junior Member Butcher's Avatar
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    Quote Originally Posted by MonteSS454 View Post
    Pulling it tonight, hoping for the best. Gotta rig up the wiring to swap 02 sensors because of my headers, am doing that soon.
    well good luck let us know how it turns out

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    Junior Member MonteSS454's Avatar
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    No go on the o2 sensor.

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    Member foxman92's Avatar
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    Quote Originally Posted by MonteSS454 View Post
    No go on the o2 sensor.
    KNOCK SENSOR'S, try to change those, im telling you that fixed my buddies t/a.. not to hard to change them, just pull the intake off, and they sit in the valley...only take about 1 1/2 hours to change them and be driving the car...

  19. #19
    Junior Member MonteSS454's Avatar
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    Driver side head checked out good internally, ran out of light for the passenger side.........I noticed something though from a cold start it purrs like a kitten, once it gets up to temp all hell breaks loose!

  20. #20
    Junior Member Butcher's Avatar
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    Quote Originally Posted by MonteSS454 View Post
    Driver side head checked out good internally, ran out of light for the passenger side.........
    your Ps side will be fine also.....dont waste you time...

    Quote Originally Posted by MonteSS454 View Post
    I noticed something though from a cold start it purrs like a kitten, once it gets up to temp all hell breaks loose!
    Dude your 02s are fucked up...

    1 or both of your 02s still thinks your motor is in warm up mode when it is hot, which makes the pcm dump fuel into that bank of cyl causing your misfire....which I have been sayin

    replace both of your front 02s w/ this part# from napa Bosch 13111


    Anyone else w/ info?????
    Last edited by Butcher; 07-23-2009 at 10:25 PM.

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