Hesitation/Sag/Stumble

Symptom: Momentary lack of response when the accelerator is pushed down. Can occur at any speed. Usually most severe from a stop or initial take off. Engine may stall if condition is bad enough.

POSSIBLE CAUSE ACTION

CHARGING SYSTEM MALFUNCTION - Check battery voltage.

- Check Generator voltage output.

IGNITION SYSTEM MALFUNCTION - Scope check Ignition System. Check SECONDARY CIRCUIT firing Kv and spark duration.
SEE IGNITION SYSTEM/OSCILLOSCOPE PATTERNS.

- Remove spark plugs and inspect for: cracks, excessive wear, improper gap, burned electrodes, and wet or heavy deposits. Replace as necessary.


- Inspect spark plug wires for proper plug wire routing, crossfire between spark plugs or wires shorting to ground.

- Check IGNITION TIMING for excessive spark advance or retard.
SEE IGNITION SYSTEM/ TIMING SPECIFICATIONS

ENGINE MECHANICAL MALFUNCTION - Check COMPRESSION Perform a compression check, and cylinder leakage test, look for sticking or leaking valves.

- Check for VACUUM LEAKS inspect Intake manifold, gasket(s), and hoses.

EMISSIONS COMPONENT MALFUNCTION - Check EGR valve for premature opening.

- Check EGR Transducer for proper operation.

FUEL SYSTEM MALFUNCTION - Check fuel pressure.

- Check for lean Air-Fuel mixture, (O2S Sensor output).

- Perform injector balance test.

- Check fuel quality.

- Check Throttle Position Sensor for proper operation.