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4.23
FUEL INJECTION
4
FUEL SYSTEM 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 boot, gasket or
grommet)
• Throttle stop screw tampering - replace throttle body
• Failed Sensor or disconnected wiring
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
• Failed Sensor or disconnected wiring
• Throttle stop screw tampering - replace throttle body
POOR IDLE
Symptom: Idle Too High (If greater than 1300 RPM when
engine is warm)
• Throttle stop screw tampering - replace throttle body
• Throttle cable sticking, improperly adjusted, routed
incorrectly
• Failed Sensor or disconnected wiring
• IAC stuck or inoperative
• Intake air leak
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 - replace throttle body
• Failed Sensor or disconnected wiring
Symptom: Erratic Idle
• Throttle cable incorrectly adjusted
• Air Leaks, dirty injector
• TPS damaged or adjusted
• Tight valves
• Belt dragging
• Dirty air cleaner
•Engine worn
• Spark Plug fouled
• Throttle stop screw tampering - replace throttle body
• Failed Sensor or disconnected wiring
The correct position of the throttle body idle
stop is established and set at the factory. Do not
loosen the throttle body idle stop or alter the
stop position in any fashion. If the stop is
repositioned, the entire throttle body assembly
must be replaced.