Spectrum 3.0L GM - Backfire

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BACKFIRE
Checks Action
DEFINITION: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping
noise.
Preliminary Check None.
Ignition System Checks
NOTE: LPG requires higher secondary ignition system voltages for the
equivalent gasoline operating conditions.
 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 (oil fouling).
 Cracks.
 Wear.
 Improper gap.
 Burned electrodes.
 Heavy deposits.
Engine Mechanical
Check
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 flash or other restric-
tions.
Fuel System Checks Perform a fuel system diagnosis. Refer to Fuel System Diagnosis.