p0300 Engine Misfire
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Northstar Engines and System Technical Discussion Discussion, p0300 Engine Misfire in Cadillac Engine Technical Discussion; About a month ago my belt tensioner started squeaking on my '00 STS. After spraying it for a few days ...
  1. #1
    RazorSpikes is offline Cadillac Owners Member
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    p0300 Engine Misfire

    About a month ago my belt tensioner started squeaking on my '00 STS. After spraying it for a few days with wd-40 the noise gradually went away. Today my car started running really rough. Then the check engine light starts blinking. I pulled the code P0300 (Engine Misfire). Could a bad belt tensioner cause this or should I check the plugs or something else?

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    AJxtcman's Avatar
    AJxtcman is offline Cadillac Owners Connoisseur
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    Re: p0300 Engine Misfire

    Quote Originally Posted by RazorSpikes View Post
    About a month ago my belt tensioner started squeaking on my '00 STS. After spraying it for a few days with wd-40 the noise gradually went away. Today my car started running really rough. Then the check engine light starts blinking. I pulled the code P0300 (Engine Misfire). Could a bad belt tensioner cause this or should I check the plugs or something else?
    Yes it can cause a P0300, but it won't be your problem.

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    AJxtcman's Avatar
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    Re: p0300 Engine Misfire

    I have seen an Auto Transfer Case cause a P0300, but never a belt tensioner. The Tensioner would cause the DTC to set, but the engine would run fine with out a misfire

  5. #4
    RazorSpikes is offline Cadillac Owners Member
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    Re: p0300 Engine Misfire

    Quote Originally Posted by AJxtcman View Post
    I have seen an Auto Transfer Case cause a P0300, but never a belt tensioner. The Tensioner would cause the DTC to set, but the engine would run fine with out a misfire
    Would you agree that I should change the plugs or coil pack?

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    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: p0300 Engine Misfire

    The belt tensioner causes a POOP300. That's kinda like a blivvet.
    Don't mess with Binky Bear!


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    fubar569 is offline Cadillac Owners Fanatic
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    Re: p0300 Engine Misfire

    Quote Originally Posted by dkozloski View Post
    The belt tensioner causes a POOP300. That's kinda like a blivvet.
    roflcopter!!!!

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    RazorSpikes is offline Cadillac Owners Member
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    Re: p0300 Engine Misfire

    i changed the plugs with oe ac delco but the check engine light is still on and it is still running rough. What's causing the engine misfire?

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    dkozloski's Avatar
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    Re: p0300 Engine Misfire

    Let's see if we have this right. You own two Cadillacs and know little or nothing about machinery or cars and are unwilling to take a car with potentially a serious and expensive problem to a real mechanic. A misfiring car can quickly ruin a catalytic convertor. Penny wise and pound foolish.
    Don't mess with Binky Bear!


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    Re: p0300 Engine Misfire

    Quote Originally Posted by RazorSpikes View Post
    i changed the plugs with oe ac delco but the check engine light is still on and it is still running rough. What's causing the engine misfire?
    Do you have a FSM? If not I would get one. It will have a trouble shooting
    tree to follow for that code. It could be the coil pack or an injector problem.
    If you just want to try replacing something, replace both coil packs.
    If that doesn't fix it you can always sell the old ones on e-bay.

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    RazorSpikes is offline Cadillac Owners Member
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    Re: p0300 Engine Misfire

    Quote Originally Posted by dkozloski View Post
    Let's see if we have this right. You own two Cadillacs and know little or nothing about machinery or cars and are unwilling to take a car with potentially a serious and expensive problem to a real mechanic. A misfiring car can quickly ruin a catalytic convertor. Penny wise and pound foolish.
    My CTS hasn't had a problem since I bought it and its still under warranty. I just bought the STS a few months ago and you are right I don't know a whole lot about cars but I learn quick. I read that a few people eliminated the engine misfire by changing the spark plugs so for a mear $50 investment with the opportunity to learn I thought I'd give it a try. I didn't realize that this problem was as serious of a matter as you describe so I will have it checked by one of the pro's.

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    Re: p0300 Engine Misfire

    Quote Originally Posted by RazorSpikes View Post
    Would you agree that I should change the plugs or coil pack?
    coil pack are the norm. If it has about 90k+ change the plugs.

  13. #12
    AJxtcman's Avatar
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    Re: p0300 Engine Misfire

    Quote Originally Posted by dkozloski View Post
    The belt tensioner causes a POOP300. That's kinda like a blivvet.
    Do you understand how the PCM monitors for misfires?
    Drive belts, alternators, TCC systems can cause false misfires.

  14. #13
    dkozloski's Avatar
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    Re: p0300 Engine Misfire

    The PCM computes the projected position of the next and successive tachometer pulses. Anything that can disturb the engine rotation and displace the pulse can appear to be a misfire. My Ford Ranger will detect hard transmission shifts as misfires. A belt tensioner would have to be practically locking up with the bearings jumping over one another to be detected as misfires. I don't see one that can be quieted by squirting WD-40 on it as being in this bad of a condition.
    Don't mess with Binky Bear!


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    RazorSpikes is offline Cadillac Owners Member
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    Re: p0300 Engine Misfire

    Paid Firestone $99 for a diagnostic test. The results were Bank 2 Coil 4 was dead. He quoted me $399 for a new coil plus $50 to install it. He also recommended I get a fuel system tune up for another $200 because my injectors may be clogged. The total was like $675. After replacing the plugs last night I think I can do the coil but what about the fuel system. Any tips?

  16. #15
    AJxtcman's Avatar
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    Re: p0300 Engine Misfire

    Quote Originally Posted by dkozloski View Post
    The PCM computes the projected position of the next and successive tachometer pulses. Anything that can disturb the engine rotation and displace the pulse can appear to be a misfire. My Ford Ranger will detect hard transmission shifts as misfires. A belt tensioner would have to be practically locking up with the bearings jumping over one another to be detected as misfires. I don't see one that can be quieted by squirting WD-40 on it as being in this bad of a condition.
    I guess you will get a lession on misfire detection from a young one.

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