Service manual

G420F(FE) Service Manual 267 Chapter 8. Basic Troubleshooting
Detonation / Spark Knock
A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change
with throttle opening (similar to the sound of hail striking a metal roof).
PRELIMINARY CHECKS
Perform the visual checks as described at start of “ Basic Troubleshooting” chapter.
PROBABLE CAUSE CORRECTIVE ACTION
Fuel system
malfunction
Check for proper fuel level:
• Check for LPG vapor from LPG liquid outlet valve on tank.
• Fill fuel container. Do not exceed 80% of liquid capacity.
Check fuel pressure.
To determine if the condition is caused by a rich or lean system, the vehicle
should be driven at the speed of the complaint. Monitoring with the Service
tool will help identify problem.
Cooling system malfunction
Check for obvious overheating problems:
• Low engine coolant
• Loose water pump belt
• Restricted air flow to radiator, or restricted water flow through radiator
• Inoperative electric cooling fan
• Correct coolant solution should be a mix of anti-freeze coolant (or
equivalent) and water
• High coolant temperature
Ignition system
malfunction
Check ignition timing. See application manual.
Check spark module wiring.
Exhaust system malfunction
Check exhaust backpressure.
Check for debris clogging the catalyst.
Check that pre-catalyst O2 sensor is functioning.
Engine mechanical
Check for excessive oil in the combustion chamber and/or blow by from
excessive PCV flow.
Check combustion chambers for excessive carbon build up.
Check combustion chamber pressure by performing a compression test.
Check for incorrect basic engine parts such as cam, heads, pistons, etc.
Related MIL Faults:
EST faults
Encoder error
High coolant temperature faults