ELECTRONIC FUEL INJECTION
5-117
EFI TROUBLESHOOTING
Fuel Starvation / Lean Mixture
Symptoms: Hard start or no start, bog, backfire, popping
through intake / exhaust, hesitation, detonation, low power,
spark plug erosion, engine runs hot, surging, high idle, idle
speed erratic.
• No fuel in tank
• Restricted tank vent, or routed improperly
• Fuel lines or fuel injectors restricted
• Fuel filter plugged
• Fuel pump inoperative
• Air leak in system
• Intake air leak (throttle shaft, intake ducts, airbox or air
cleaner cover)
• Incorrect throttle stop screw adjustment
Rich Mixture
Symptoms: Fouls spark plugs, black, sooty exhaust smoke,
rough idle, poor fuel economy, engine runs rough/ misses,
poor performance, bog, engine loads up, backfire.
• Air intake restricted (inspect intake duct)
• Air filter dirty/plugged
• Poor fuel quality (old fuel)
• Fouled spark plug
• TPS setting incorrect
• Injector failure
Poor Idle
Symptom: Idle Too High (If greater than 1300 RPM when
engine is warm)
• Throttle stop screw set incorrect
• Throttle cable sticking, improperly adjusted, routed
incorrectly
Symptom: Idle Too Low (if less than 900 RPM when engine
is warm)
• Plugged air filter
• Leaking injector (rich condition)
• Belt dragging
• Throttle stop screw tampering
Symptom: Erratic Idle
• Throttle cable incorrectly adjusted
• Air Leaks, dirty injector
• TPS damaged or adjusted
• Tight valves
• Ignition timing incorrect
• Belt dragging
• Dirty air cleaner
• Engine worn
• Spark Plug fouled
• Throttle stop screw set incorrectly (out of sync with ECU)
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