ASE A1 Engine RepairCylinder Head and Valve TrainMedium
A client complains of an engine that runs rough, has reduced power, and occasionally backfires through the exhaust. A cylinder compression test reveals significantly lower readings on two adjacent cylinders. What is the most probable cause of this issue?
- AClogged fuel injector in one cylinder
- BWorn piston rings in both cylinders
- CBlown head gasket between the two cylinders
- DFaulty spark plug in both cylinders
Show answer & explanationAnswer & explanation
Correct answer: C. Blown head gasket between the two cylinders
Significantly lower compression readings on two adjacent cylinders, accompanied by rough running and exhaust backfiring, are classic symptoms of a blown head gasket allowing combustion pressure to leak between those cylinders.
Why the other options are wrong
- A. A clogged fuel injector would affect only one cylinder and typically wouldn't cause low compression.
- B. Worn piston rings could cause low compression, but it's less likely to affect two adjacent cylinders simultaneously and significantly to this extent without other symptoms like excessive oil consumption.
- D. Faulty spark plugs would cause misfires but would not directly cause low compression readings.
Blown Head Gasket (Adjacent Cylinders)
A failure of the cylinder head gasket between two adjacent cylinders, leading to a loss of compression and combustion gas leakage between them.
- Causes low compression in adjacent cylinders.
- Can lead to engine overheating or coolant loss.
- Symptoms include rough running, reduced power, exhaust backfire.
Memory trick: Adjacent low compression points to a gasket's demise.