ASE A1 Engine RepairFuel, Emissions, and Ignition Systems (General)Easy
A technician is performing a basic ignition system diagnosis on a vehicle with a no-start condition. The technician confirms there is fuel pressure and proper engine cranking. What is the next logical step to diagnose the ignition system?
- AInspect the fuel injectors.
- BPerform a compression test.
- CCheck for spark at the spark plugs.
- DReplace the ignition coil.
Show answer & explanationAnswer & explanation
Correct answer: C. Check for spark at the spark plugs.
In a no-start condition where fuel and cranking are confirmed, the next logical step in ignition system diagnosis is to verify the presence of spark. This directly checks if the ignition system is producing the necessary high voltage to ignite the air-fuel mixture.
Why the other options are wrong
- A. Inspecting fuel injectors is part of fuel system diagnosis; the question specifies diagnosing the ignition system after fuel is confirmed.
- B. A compression test assesses engine mechanical health, which is usually checked after confirming spark and fuel, or if spark/fuel are present but the engine still doesn't start or runs poorly.
- D. Replacing an ignition coil without testing is premature and may not be the root cause.
No-Start Ignition Diagnosis
The systematic process of identifying the fault within the ignition system when an engine cranks but does not start, typically starting with verifying spark presence.
- Requires three elements: spark, fuel, compression.
- After confirming fuel and cranking, spark is the next check.
- Can be checked with a spark tester or by observing a plug.
Memory trick: Crank, Fuel, Spark, Compression – the engine's core mission!