What Causes a Rich Fuel System?

[SaraLynn]

Fuel system running rich can be caused by the following reasons: 1. High fuel mixture ratio: The engine's fuel mixture ratio is too high, possibly due to slight injector leakage, faulty coolant temperature sensor, or potential malfunctions of the MAF sensor and oxygen sensor. 2. Insufficient cylinder pressure: The engine's cylinder pressure is inadequate with too low compression ratio. This can usually be identified by listening to the engine performance, or by measuring cylinder pressure if necessary. Low cylinder pressure typically indicates mechanical issues such as problems with pistons, rings, cylinders, or valves. 3. Weak spark with high voltage: This may be caused by spark plugs with carbon deposits, small gaps, or poor performance, leading to electrical leakage or misfiring.