How the system works
A simplified combustion-engine cycle; fueling, ignition, valve timing, and other engine designs vary.
- 01IntakeThe piston moves down as air enters. Fuel delivery depends on engine design.
- 02CompressionValves close and the piston rises, compressing the cylinder contents.
- 03PowerCombustion raises pressure and pushes the piston down. Ignition method varies.
- 04ExhaustThe piston rises and pushes spent gases out through the exhaust valve.
Major components in context
Creates the ignition gap in a spark-ignition engine
Open componentIgnition coilRaises voltage for the spark event
Open componentFuel injectorMeters fuel when commanded
Open componentMAF sensorReports measured intake airflow on systems that use one
Open componentSeals, compresses, times, and converts combustion force
System contextSymptom patterns and first direction
Cranks but will not start
Separate ignition, fuel, compression, timing, and authorization evidence.
Follow the diagnostic pathSYMPTOMRough idle or shaking
Decide whether combustion is uneven or vibration is being transmitted mechanically.
Follow the diagnostic pathSYMPTOMMisfire code or flashing warning
Reduce load and diagnose promptly; a code identifies detection, not the failed part.
Follow the diagnostic pathSYMPTOMOil leak or oil loss
Locate the fluid and protect the engine before separating external leakage from consumption or another fluid.
Follow the diagnostic pathA system-level diagnostic method
Record operating conditions and warning behavior
Scan every relevant module before clearing evidence
Compare related data rather than judging one value alone
Choose the least invasive test that can reject a cause group
Verify the repair under the original conditions
Evidence worth preserving
Freeze-frame and fault context
Cylinder contribution or misfire pattern
Air, fuel, and ignition test results
Compression or mechanical timing evidence when justified
Use the VIN, installed equipment, current manufacturer information, and applicable safety rules.
Safety and professional boundary
Heat and moving-part hazards
Keep hands, clothing, leads, and tools clear of belts, fans, and other moving parts. Exhaust and cooling components can remain hot after shutdown.