ASE G1 Auto Maintenance and Light RepairEngine SystemsMedium
A technician is diagnosing an engine that cranks normally but will not start. They have confirmed there is good spark and fuel pressure. Which of the following tests should the technician perform NEXT to determine the cause of the no-start condition?
- AInspect the fuel injectors for proper operation.
- BPerform a compression test.
- CCheck for proper engine timing.
- DTest the ignition coil primary and secondary resistance.
Show answer & explanationAnswer & explanation
Correct answer: B. Perform a compression test.
If an engine has spark and fuel, the next most critical factor for combustion is compression. A compression test will quickly determine if the engine has sufficient cylinder pressure to ignite the air-fuel mixture.
Why the other options are wrong
- A. While important, injector operation is downstream from the basic need for compression. If there's no compression, even perfect injection won't result in a start.
- C. Engine timing is important, but a compression test is a more fundamental check for a no-start condition when spark and fuel are present.
- D. Spark has already been confirmed, so further testing of the ignition coils would be redundant at this stage.
Engine Cranks, No Start Diagnosis
When an engine cranks but fails to start, the diagnostic process involves systematically checking the three fundamental requirements for combustion: spark, fuel, and compression.
- All three elements (spark, fuel, compression) must be present for an engine to start.
- Systematic diagnosis saves time and prevents unnecessary part replacement.
- A compression test is critical if spark and fuel are confirmed.
Memory trick: Spark, Fuel, Compression: The engine's starting mission!