Service manual

G424F(FE) Service Manual 241 Chapter 8. Basic Troubleshooting
Rough, Unstable, Incorrect Idle, or Stalling
Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately dies.
PRELIMINARY CHECKS
Perform the visual checks as described at start of “Basic Troubleshooting” chapter.
Check for vacuum leaks.
Check that SECM grounds are clean and tight. See SECM wiring diagram
PROBABLE CAUSE CORRECTIVE ACTION
Fuel system
malfunction
Monitor oxygen feedback to help identify the cause of the problem. If
the system is running lean or if the system is running rich evaluate
further i.e. dither valve duty cycle and injector pulse width.
Check for incorrect minimum idle speed that may be caused by foreign
material accumulation in the throttle bore, on the throttle valve, or on
the throttle shaft.
Check that the injectors are clean and functioning.
Check for liquid fuel in propane pressure regulator hose. If fuel is
present, replace regulator assembly.
The pre-catalyst oxygen (O2) sensor should respond quickly to
different throttle positions. If it does not, then check the pre-catalyst O2
sensor for contamination. If the pre-catalyst O2 sensor is aged or
contaminated, the SECM will not deliver correct amount of fuel,
resulting in a drivability problem.
Fuel container empty
Check for LPG vapor from LPG liquid outlet valve on tank.
Fill fuel container. Do not exceed 80% of liquid capacity.
Ignition system
malfunction
Check ignition system; wires, plugs, rotor, etc.
LPG pressure regulator malfunction
Test regulator operation and pressure.
See Chapter 6 Tests and Adjustments
Air/fuel mixer malfunction Check mixer.
Component malfunction
Check throttle for sticking or binding.
Check PCV valve for proper operation by placing finger over inlet hole
in valve end several times. Valve should snap back. If not, replace
valve.
Check alternator output voltage. Repair if less than 9 or more than 16
volts.
Engine mechanical
Perform a cylinder compression check.
See Chapter 3 Engine Mechanical System.