Checks
| Action
|
DEFINITION: A surging or jerking that follows engine speed,
usually more pronounced as the engine load increases.
|
Preliminary
Checks
| Refer to Important Preliminary Checks in
Symptoms
.
|
Fuel System Checks
|
| • | Check the high and low pressure lock-off valves / circuits for
proper operation. |
|
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. |
| • | Check for fouled spark plugs. |
| | If fouled spark plugs are indicated the reason for the fouling must
be found and corrected. |
| • | Check for faulty spark plug wires. |
| • | Check for an open ignition system ground (if equipped). |
| • | Ensure the distributor is properly adjusted. |
|
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 |
| • | Casting flash in the intake or exhaust manifold passages |
|
Additional Checks
| Check for electromagnetic interference (EMI) by checking
for the following:
| • | Monitoring engine speed on the scan tool may indicate EMI is present. |
| | A sudden increase in scan tool engine speed while actual engine speed
remains constant indicates EMI is present. |
| • | EMI on the ignition control circuit may cause a missing condition. |
| • | Re-routing of the secondary wires may be required to remove the
EMI. |
|
