Doosan D20S-5 Operation & Maintenance Manual page 137

BACKFIRE
Checks
DEFINITION: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping
noise.
Preliminary Checks
Ignition System
Checks
Engine Mechanical
Check
Fuel System
Checks
None
Important! LPG, being a gaseous fuel, requires higher secondary ignition
system voltages for the equivalent gasoline operating conditions. The ignition
system must be maintained in peak condition to prevent backfire.
• Check for the proper ignition coil output voltage using the spark tester J26792 or
the equivalent.
• Check the spark plug wires by connecting an ohmmeter to the ends of each wire
in question. If the meter reads over 30,000 ohms, replace the wires.
• Check the connection at ignition coil.
• Check for deteriorated spark plug wire insulation.
Remove the plugs and inspect them for the following conditions:
• Wet plugs.
• Cracks.
• Wear.
• Improper gap.
• Burned electrodes.
• Heavy deposits.
Important! The LPG Fuel system is more sensitive to intake manifold leakage than a
gasoline fuel supply system.
Check the engine for the following:
• Improper valve timing.
• Engine compression.
• Manifold vacuum leaks.
• Intake manifold gaskets.
• Sticking or leaking valves.
• Exhaust system leakage.
• Check the intake and exhaust system for casting ash or other restrictions.
Perform a fuel system diagnosis. Refer to LPG Fuel System Diagnosis.
Action
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Operation Section