Q: codep0300 multiple misfires

asked by on December 28, 2017

as soon as i turn it on the Check engine light starts flashing codeP0300 random misfires, engine starts really high idle, wants to shut off, engine shakes alot, smells like fuel, some black liquid comes out the exhaust, loss power, boggs at wot, also gives me a MAF code. already tried new MAF sensor, spark plugs, and wires, fuel filter changed, its a 2006 Gmc Sierra 1500 5.3L 143k miles it started when i had some some Edelbrock shorties set of headers installed. it also has an air intake exhaust and never had it tuned.

My car has 143000 miles.
My car has an automatic transmission.

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Given the number of symptoms that you have described, there might be more than one basic underlying cause of the poor operation. Also, mechanical failure such as poor cylinder compression and/or sticking valves would have to be ruled out. Generally, cylinder misfiring is due to faulty spark plugs, low compression, damage or excessive wear of spark plug wires and/or coils, faulty fuel injectors, clogged EGR valves or tubes, burned valves, improper ignition timing, vacuum leaks, leaking head gasket, faulty camshaft sensor, faulty crankshaft sensor, faulty mass air flow sensor, faulty oxygen sensor, faulty throttle position sensor, faulty catalytic converter, and many other causes. If you want the cause(s) of the poor operation and the misfiring pinpointed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a misfiring diagnostic and the responding certified mechanic will get this diagnosed and resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic.

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