VALVE-PRIORITY 1109734 - Caterpillar

Probable Causes
Cylinder misfire
Air/Fuel ratio
Needle valves
Leaks
Valve lash
Check valve
Excessive depositsRecommended Actions
Table 1
Troubleshooting Test Steps Values Results
1. Check for a Cylinder Misfire
Note: Although the fuel does not ignite, fuel is still supplied to a cold cylinder. The other cylinders must burn more fuel in order to maintain the load. This increases fuel consumption.
Misfire
Result: There is not a cylinder misfire.
Proceed to Test Step 2.
Result: There is a cylinder misfire.
Repair: Troubleshoot the cause of the misfire. Refer to Troubleshooting, "Engine Misfires, Runs Rough, or Is Unstable" for additional information.
If the problem is not resolved, proceed to Test Step 2.
2. Check the Air/Fuel Ratio
Note: A change in the fuel energy content will change the air/fuel ratio.
A. Obtain a fuel analysis.
Note: If the quality of the gas is inconsistent, obtain several analyses over a period of time.
B. Enter the data into Caterpillar Software, LERW4485, "Gas Engine Rating Pro (GERP)".
C. Verify that the fuel supply pressure is adequate and stable.
D. Verify that the exhaust emissions are correct.
Air/Fuel Ratio
Result: The air/fuel ratio is OK.
Proceed to Test Step 3.
Result: The air/fuel ratio is NOT OK.
Repair: Use Cat ET to program the results for the "Fuel Specific Heat Ratio", "Fuel Quality", and "Gas Specific Gravity" parameters. Refer to Systems Operation, "Electronic Control System Parameters" for additional information.
Program the "Fuel Quality" parameter to the average value of the LHV. Adjust the engine operation according to Testing and Adjusting, "BTU and Precombustion Chamber Adjustments".
If the problem is not resolved, proceed to Test Step 3.
3. Check the Needle Valves Adjustments
If the setting for the fuel's LHV is too low, the air/fuel ratio will be too rich.
A. If the needle valves require adjustment, do the following procedure:
- Fully close all of the needle valves.
- Open all of the needle valves 2.5 turns.
- Enter "Engine Prechamber Calibration" mode in Cat ET.
- Record engine average burn time.
- Adjust each needle valve until all cylinders' burn times are within +/- 0.12 milliseconds of the engine average burn time.
- Exit "Engine Prechamber Calibration" mode.
Note: The recommended position of the needle valve is 2.5 turns open.
B. Make sure that the fuel lines for the needle valves are not clogged.
Note: If the needle valve moves freely, the position of the needle valve may change during engine operation due to vibration.
Needle Valves
Result: The needle valves are OK.
Proceed to Test Step 4.
Result: The needle valves are NOT OK.
Repair: Adjust the needle valves to the correct setting. Refer to Testing and Adjusting, "BTU and Precombustion Chamber Adjustments" for additional information.
If the problem is not resolved, proceed to Test Step 4.
Gaseous fuel is present. Personal Injury or Death can result from an open flame or spark igniting the gaseous fuel causing an explosion and/or fire. Always use a gas detector to determine the presence of gaseous fuel when maintaining and servicing. Contact your local gas provider immediately for assistance in the event of a leak.
Table 2
Troubleshooting Test Steps Values Results
4. Inspect the Fuel System for Leaks
Note: Always use a gas detector to determine the presence of gaseous fuel. Contact your local provider of