Code PO300 random misfires - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 09-25-2016, 08:33 PM   #1
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Default Code PO300 random misfires

Having issues, especially driving up hills. First thing I did, changed upstream O2 sensor (was giving a code for that too), and replaced plugs w/Delco Iridiums. Didn't seem to help much, though less CEL. Changed the plug wires last weekend, wasn't sure of any improvement. But after a week, I'd say some improvement at least, but still getting this code. What to look at next?
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Old 09-26-2016, 06:29 AM   #2
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Check fuel pressure.....pump may be on it'* way out.
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Old 09-26-2016, 08:18 AM   #3
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Yup. Fuel pressure is next on the list.
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Old 09-26-2016, 09:42 PM   #4
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I haven't had a chance to change the fuel filter, so there'* a possibility...
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Old 09-28-2016, 06:38 PM   #5
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misfire with load in overdrive, check coils.
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