Q: only passenger side plug is carbon build up driver side is clean change plug doing same thing

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my car was hesitate when go up hill and start to go change plug and wire only passenger side plug was heavy carbon build up driver side was clean burn after 100 mile car was acting up same problem check plug only passenger side plug carbon build up again

My car has 90000 miles.
My car has an automatic transmission.

Hello, thank you for writing in. The most common cause of carbon build up on the spark plugs is unburned fuel, also known as "running rich". Despite the assumption that the injectors are to blame, it usually has more to do with how the spark plug is firing. Since it has happened to two separate sets of plugs, you are concerned with the ignition circuit at that side or plug. The coils and wires are the first to rule out. Oil being burned in the engine can also cause extra carbon deposits. If the ignitions system checks out, start looking for signs of an internal oil leak. For more help with diagnostics and repairs, contact our service department to schedule an appointment.

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If only one side of the motor is clogged with excessive carbon build-up, it may represent a lean mixture issue with the fuel injection system. Unless you are experiencing loss of power, fuel mileage of the engine is running extremely hot, I wouldn’t worry about it. If you experience those symptoms, have a professional mechanic inspect the fuel system for issues.

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