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HELP!! Missfire

This is a discussion on HELP!! Missfire within the General Help forums, part of the LSx Technical Help Section category; Ok guys, my car has been missfiring for the past 2 weeks and has not stopped. It P0300 i think, ...

  1. #1
    Senior Member rajiv1998's Avatar
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    HELP!! Missfire

    Ok guys, my car has been missfiring for the past 2 weeks and has not stopped. It P0300 i think, its def a random missfire. I just dont know what the fuck it is and its driving me nuts driving it!! I checked everything and its all good. Plugs, wires, coilpacks. I had a few friends come check her out to and still nothing. I had my mechanic look at it, and he said when he drove it, it rain fine, and it did for a few hours. The only thing i can think off is a sensor maybe?? My water pump is leaking a bit and im getting that fixed first thing tommorow at 6am (since i will be at college, i told my mechanic to swap it out) Maybe coolant got onto a sensor or wire and thats wuts causing it?? I also made a thread a few weeks back regarding a bad cat, but it turns out the previous owner gutted one out, and thats the one that is throwing off codes. Its hallow and theres nothing in it. So maybe a little coolant got into something it wasnt suppose to and thats whats causing it, or could it be the dam cat?? Any1??

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    old timer blue02Z's Avatar
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    how many miles and mods? fuel injectors will cause a misfire as well. myabe look into cleaning them

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    Veteran 0rion's Avatar
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    how many miles on the fuel filter also?

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    Senior Member rajiv1998's Avatar
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    The cars has a lil over 95k miles. I didnt touch the injectors, but maybe the previouis owner might have, never checked it out. Yeah, i think i might need a new fuel filter as well. Any brand in perticular? Is it worth changing injectors?? If so, i most likley will get some SVO's.

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    Veteran 0rion's Avatar
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    well, I wouldn't just run out and buy injectors on a hunch. I just use any parts store fuel filter, I'm not picky about that stuff though. You could try changing out the fuel filter and running some injector cleaner through the car and see if that helps you any. Cheap and easy thing to rule out.

    any mods on the car?

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    Senior Member rajiv1998's Avatar
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    Quote Originally Posted by 0rion View Post
    well, I wouldn't just run out and buy injectors on a hunch. I just use any parts store fuel filter, I'm not picky about that stuff though. You could try changing out the fuel filter and running some injector cleaner through the car and see if that helps you any. Cheap and easy thing to rule out.

    any mods on the car?
    Mostly stock....SLP lid and exhaust w/3" cutout, NGK plugs, MSD wires. Those are the only things that i can think of that might have anything to do with it. I ran injector cleaner a while back but i dont know how often i should do it. Defenatley gonna try and and swap the fuel filter. I just put in a new water pump, and it seemed to run fine for like 5 min then it went back to doing the same thing. U think it could prehaps be the cat code thats throwing it off. My cat is gutted, so my SES light came on, but in reality there is nothing wrong with the cat.

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    I'd visit gearchatter.com for your year and look up P0300 for the misfire and P0420/P0430 for the post cat code to get some ideas. Something else you can try is start/rev the car in the dark and look for any arcing around the coils/plugs/wires, etc.

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    Senior Member rajiv1998's Avatar
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    Quote Originally Posted by 2001NBMZ28 View Post
    I'd visit gearchatter.com for your year and look up P0300 for the misfire and P0420/P0430 for the post cat code to get some ideas. Something else you can try is start/rev the car in the dark and look for any arcing around the coils/plugs/wires, etc.
    gear chatter would not let me log on, i dont know why. If any1 here is a member over there, can theyh do me a favor and make a post??

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    You don't need to log on to see the DTC codes/descriptions/diagnostics. Just go to www.gearchatter.com/ and click on 1998 F-Body DTC, click on the codes.

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    I had a random missfire on mine which turned out to be the crank position sensor (CPS). (Located behind the starter)

    After the shop replaced it it still missfired.
    Turns out that the sensor has to be synchronized with the crank for the missfire to go away. Not just replace and go.

    They said the mechanics at the local GM dealer just found out about this issue a couple years ago. They had never had to sync a CPS before.

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    Senior Member Orcus79's Avatar
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    I was flipping though my service manula for the 2000 year F-bodies and stumbled across that the EGR valve can set off a misfire code as well.

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    Senior Member rajiv1998's Avatar
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    Quote Originally Posted by Orcus79 View Post
    I was flipping though my service manula for the 2000 year F-bodies and stumbled across that the EGR valve can set off a misfire code as well.

    ?? Explain, my EGR is on the car.

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    Senior Member Orcus79's Avatar
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    Yea, if the EGR valve is not operating porprerly it can cause the p0300 code for some reason *shrugs*. Right from p 6-1964

    Too much EGR flow causes any of the following conditions to occur:

    The engine stalls after a cold start
    The engine stalls during closed throttle conditions
    The vehicle surges during a cruise condition
    A rough Idle
    ADTC P0300

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    Quote Originally Posted by Orcus79 View Post
    Yea, if the EGR valve is not operating porprerly it can cause the p0300 code for some reason *shrugs*. Right from p 6-1964

    Too much EGR flow causes any of the following conditions to occur:

    The engine stalls after a cold start
    The engine stalls during closed throttle conditions
    The vehicle surges during a cruise condition
    A rough Idle
    ADTC P0300
    Mine does everyone of these. Does anyone know what I would need to buy or do to fix this EGR problem?

    Thanks

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    Senior Member Orcus79's Avatar
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    The quick fix would be to take it off and carefully clean the carbon out of it. Other wise look at replacing it in its entiity. I am not sure what parts ofteh valve its self can be reaplced, but that is where I would start.

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    Retired NOT tired SteveC's Avatar
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    Quote Originally Posted by DvLzArchAngL View Post
    I had a random missfire on mine which turned out to be the crank position sensor (CPS). (Located behind the starter)

    After the shop replaced it it still missfired.
    Turns out that the sensor has to be synchronized with the crank for the missfire to go away. Not just replace and go.

    They said the mechanics at the local GM dealer just found out about this issue a couple years ago. They had never had to sync a CPS before.
    The "Misfire code" will trip the dreaded P1336 code which is the CPS, you need a tech II or EFI live to run the sync. You set the tech II on CPS relearn, with the vehicle in park, you raise the idle to 4K until the engine starts to stumble, you let off the gas, and during deacceleration it relearns the sync. YOU DO THIS AFTER YOU HAVE SOLVED THE P0300 PROBLEM.

    SteveC

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    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by SteveC View Post
    you need a tech II or EFI live to run the sync. .....


    Or HPTuners

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