Checks
| Action
|
DEFINITION: The engine delivers less than expected power.
There is little or no increase in speed when partially applying the accelerator
pedal.
|
Preliminary Checks
|
| • | Refer to Important Preliminary Checks in
Symptoms
. |
| | Important:: Do not compare the power output of the vehicle while operating on CNG
to the vehicle operating on gasoline. Both fuels have different drive feel
characteristics.
|
| • | Verify the customers concern by comparing the power output of a similarly
equipped known good vehicle to the suspect vehicle. |
| • | Check the air filter for proper type and for dirt or restriction. |
| • | Check the transmission for proper shift pattern and downshift
operation. |
| • | Inspect the gasoline control module (VCM/PCM or ECM) for the correct
bi-fuel calibration. Program the gasoline control module if necessary. |
| • | Ensure the vehicle cargo rating is not being exceeded. |
|
Fuel System Checks
|
|
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. |
| | Important:: More timing advance is required to operate the vehicle on CNG than on
gasoline. A vehicle that operates normally on gasoline does not indicate
a fully functional knock sensor / timing system.
|
| • | Check for proper operation of the Knock Sensor system. |
| • | 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. |
|
Exhaust System Checks
| Check the exhaust system for a possible restriction.
Restrictions can include the following:
| • | A faulty catalytic converter. |
| • | Damaged or collapsed pipes. |
| • | An internally faulty muffler (may show signs of heat distress). |
|
Engine Mechanical Checks
| Check for proper engine operation by checking
for the following:
| • | Correct engine compression. |
| • | Correct engine valve timing. |
| • | A worn or incorrect camshaft. |
|
Additional Checks
|
| • | Check the EGR valve for proper operation. A stuck open valve may
cause this symptom. |
| • | Check for proper A/C compressor clutch operation. An A/C clutch
that is engaged all the time may cause this symptom. |
| • | Check for proper transmission torque converter clutch (TCC) operation
(if equipped). |
| • | Check for proper generator operation. |
| • | Check for proper operation of the accelerator pedal. A stretched
accelerator cable may cause this symptom. |
|
