Service Manual

3.28
ELECTRONIC FUEL INJECTION
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 pump inoperative
• Air leak in system
• Intake air leak (throttle shaft, intake boot, gasket or
grommet)
• Throttle stop screw tampering
• 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
Poor Idle
Symptom: Idle Too High (If greater than 1400 RPM when
engine is warm)
• Throttle stop screw tampering
• 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 1100 RPM when engine
is warm)
• Plugged air filter
• Leaking injector (rich condition)
• Belt dragging
• Throttle stop screw tampering
• Failed sensor or disconnected wiring
Symptom: Erratic Idle
• Throttle cable incorrectly adjusted
• Air Leaks, dirty injector
• TPS damaged or misadjusted
• Tight valves
• Belt dragging
• Dirty air cleaner
•Engine worn
• Spark Plug fouled
• Throttle stop screw tampering
• Failed sensor or disconnected wiring
The correct position of the throttle body
stop screw is established and set at the
factory. DO NOT remove the tamper proof
cap to adjust the throttle body stop screw or
alter its position in any manner. The stop
screw controls the air flow calibration
of the throttle body.