LS4 Performance Grand Prix GXP | Monte Carlo SS | Impala SS | LaCrosse Super

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Old 08-23-2018, 12:44 PM
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I just bought a 2007 Pontiac Grand Prix GXP with 67k miles. Filled it with 92 octane gas and drove 240 miles home and didnít have one issue while traveling at a constant 70 mph. About a mile from home the check engine light started flashing and the car was idling rough. Used my scanner and discovered code P0307 cylinder 7 misfire. Could the difference in octane cause the spark plug to foul? Iím guessing the previous owner used 87 octane due to all the soot on the exhaust tips.
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Old 08-24-2018, 09:40 AM
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Welcome. Its a DOD plug and those are usually dirtier anyway if it is still activated. Change them all, number 8 is a bitch. Always run super if you can. Post back your findings. Good luck
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