Checks
| Action
|
DEFINITION: The fuel ignites in the intake manifold, or
in the exhaust system, making a loud popping noise.
|
Preliminary
Checks
| Refer to Important Preliminary Checks in
Symptoms
.
|
Ignition System Checks
|
| | Important:: A higher secondary ignition voltage is required to operate the vehicle
on CNG than on gasoline. A vehicle that operates normally on gasoline does
not indicate a fully functional ignition system.
|
| • | Check for proper secondary ignition system voltage output using the
J 26792 spark tester. |
| • | Remove and inspect the spark plugs for the following conditions: |
| • | Check for proper ignition system operation. |
| • | Check for proper CMP sensor adjustment and operation. The CMP
Retard must be adjusted to 0 plus or minus 1 degree for proper engine operation
on CNG fuel. |
| • | Check for crossfire between sparkplugs. Check for distributor
cap or spark plug wire failure. Wetting down the secondary ignition system
with a water spray bottle may aid in locating damaged or deteriorated
components. |
|
Engine Mechanical Checks
|
Important:: The alternative fuel system works on the fumigation principle. Fumigation
systems are more sensitive to intake manifold leakage than traditional gasoline
fuel systems.
| • | Check the engine for the following: |
| - | Proper engine cylinder compression |
| - | Sticking or leaking intake or exhaust valves |
| • | Check the EGR valve for proper operation. A stuck open EGR valve
or an EGR system leak may cause this symptom. |
| • | Check the intake and exhaust system for casting flash. |
|
Fuel System Checks
| Perform fuel system diagnosis. Refer to
Fuel System Diagnosis
.
|
Additional
Checks
|
| • | Check service bulletins for control module (AF ECU, VCM/PCM or
ECM) programming updates (re-flashing). |
| • | Verify that the correct software and calibration has been programmed
into the gasoline control module (VCM/PCM or ECM). |
| • | Test for proper operation of the NGO Enable circuit. |
|
