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Thread: code P0300 why?

  1. #1
    New Member
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    1996 BAM coupe

    Default code P0300 why?

    Does anyone know what would cause code P0300 (intermittent/random misfire) to come up on a diagnostic? I had a diagnostic done about an hour ago since I had a check engine light on and have had issues recently with a rough idle (only once the engine comes up to temp). Please let me know if anyone has had this code come up and what needed to be done to correct the problem. FYI, the check engine light went off after the diagnostic was done.

    I have recently replaced the following: fuel pump, fuel filter, plugs, plug wires, EGR valve and fuel pressure regulator. In addition, I am unable to locate any vacuum leaks. Could my problem be electrical?

  2. #2
    Member LT4man's Avatar
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    96 Collectors Edition LT4

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    The PO300 trouble code is one of the most prevalent codes for the LT1/LT4 engine.

    Most of the time the issue is an electrical ignition issue.

    If you search on the internet, you will find many postings having to do with this code.

    This is a "Random Misfire" code, so any of the cylinders can cause this code to set.

    I have seen where oil from an over-oiled air filter will set this code.

    A hairline crack in the porcelain of a spark plug can be the culprit.

    A slight misfire in an ignition wire (even if the wire set is new!) can also occur.

    Premium brand name ignition wire sets should always be used.

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  3. #3
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    Yes...your problem could be electrical.

    P0300 "random misfire" is a code that sets when the misfire detection feature of the ECMs OBD2 detects misfire which is not-cylinder specific, ie: it's random.

    First thing to do is make sure all ignition components including the distributor are working properly. If you find parts which are not, replace as necessary.

    It is possible either of your two front oxygen sensors are faulty, but more diagnosic information is needed to say for sure.

  4. #4
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    1996 BAM coupe

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    Had a series of diagnostics run by an ASE certified mechanic including a vacuum leak test and was told the Optispark needs to be replaced. Cylinders 1 and 2 are not firing properly. He gave me a price for an AC Delco Optispark for 750.00, ouch. I found the same part number for the AC Delco part (1104032) online from Chandler Motor Sports on E-Bay for 134.99 with a lifetime warranty from CMS. Is this a purchase I should consider? I want to put the right Optispark on the car so just want to make sure I am doing the right thing by considering this affordable item. If anyone has purchased this item or others from CMS please let me know your thougts.

  5. #5
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    1993 Ruby Red 40th Anniversary Coupe

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    Quote Originally Posted by 96 BAM View Post
    Had a series of diagnostics run by an ASE certified mechanic including a vacuum leak test and was told the Optispark needs to be replaced. Cylinders 1 and 2 are not firing properly. He gave me a price for an AC Delco Optispark for 750.00, ouch. I found the same part number for the AC Delco part (1104032) online from Chandler Motor Sports on E-Bay for 134.99 with a lifetime warranty from CMS. Is this a purchase I should consider? I want to put the right Optispark on the car so just want to make sure I am doing the right thing by considering this affordable item. If anyone has purchased this item or others from CMS please let me know your thougts.
    Generally one gets what one pays for.

    I've not bought a CMS Opti-Spark nor the one I'm about to recommend but I would give this Petris Enterprises, Inc. - Products at try and call them if it was me. I've HEARD good things, and that SEEMS to be the general consensus.
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  6. #6
    Member Itshakes's Avatar
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    2013 Grand Sport 60th anniversary Coupe

    Help PO300 code

    If I leave my '96 LT4 sit for longer than 2 weeks, every time I drive it after sitting it displays this code. If I drive it within the 2 week time frame--no code! If it sits for longer than 2 weeks, the first time I drive it, the code sets. The check engine light does not come on right away. It displays the check engine light after about 5 minutes driving time (open loop?) I can reset the light and it never comes on again until the car sits for 2 weeks or longer. Any ideas? FYI- new opti, wires, plugs, coil, ICM, injectors, 93 octane BP fuel. There is 75K on the car, but this has been happening since 68K.

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