In generator set applications, idle stability is critical for synchronization of the generator set with the electrical grid. Follow the chart for the Recommended Inlet Manifold Pressure, with no load on the engine.
| Recommended Inlet Manifold Pressure | |
| Engine RPM | Inlet Manifold Pressure (1) |
| 900 | 40 ± 5 kPaa (5.8 ± .7 psia) |
| 1000 | 50 ± 5 kPaa (7.3 ± .7 psia) |
| ( 1 ) | kPaa is kilopascal measured in absolute pressure. |
These recommended values are provided for reference only. Parasitic loads affect the required inlet manifold pressure. The engine choke trim can and should be adjusted to a manifold pressure level that provides the optimum engine stability and the load acceptance capability for the specific application of the engine.
Electronic Choke Trim Procedure
- Set the engine operating condition to the rated speed and no load (or minimum load possible).
- Connect the DDT to the Engine Supervisory System (ESS). Display the DDT screen "number 33" by pressing the "SELECT MODE" key in order to display the "CSP MENU" (customer selectable parameters) screen "number 03". Then press the "SELECT FUNC" key to display screen "number 33". Or simply enter the "number 33" and then press the "ENTER" key.
Screen "number 33" on the DDT will display the following:
"CHOKE TRIM"
"00 40/0900 33<"
The numbers on the second line of the display are: The choke trim "OFFSET" number which indicates the amount of offset that has been entered through the "ALT1" and the "ALT2" keys. The amount of the choke trim offset "00" represents the factory default setting. "40/0900" represents the Inlet Manifold Pressure (kPaa)/Engine speed (rpm).
Note: kPaa is kilopascal measured in absolute pressure.
- On the DDT screen "number 33", when the "ALT1" or "ALT2" keys are pressed, a command signal is sent to the choke actuator in order to change the position of the choke plate.
To raise the inlet manifold pressure, press the "ALT2" key. (The offset number on the DDT screen will decrease by one every time the "ALT2" key is pressed.)
To lower the inlet manifold pressure, press the "ALT1" key. (The offset number on the DDT screen will increase by one every time the "ALT1" key is pressed.)
This process should be done slowly. Pause after every adjustment in order to allow the engine to respond to the change in the inlet manifold pressure.
Monitor the following:
- inlet manifold pressure
- stability of the engine rpm
- position of choke actuator
- position of wastegate actuator
- individual cylinder combustion burn times
- individual cylinder exhaust port temperatures
To monitor individual cylinder misfire during the choke trim process, alternate between the choke trim mode and precombustion chamber calibration mode.
- Press "SELECT MODE" key in order to display "PC CAL MODE" .
- Press "SELECT FUNC" key in order to operate the engine in the precombustion chamber calibration mode.
- Press "ALT2" key in order to display combustion BT as a non-averaged number.
- Press "ENTER" key in order to monitor the individual cylinders.
A combustion BT of greater than 10 ms should be considered a misfire. The frequency of misfire will be reduced when the engine is properly choke trimmed.
Note: Do not over choke the engine. Load acceptance capability may be reduced.
- inlet manifold pressure
- If engine stability is unacceptable after properly completing the choke trim procedure, refer to the Testing and Adjusting, "Governor Adjustment Procedure" of this manual.
Note: The position of the choke plate can be returned to the factory setting that is programmed into the personality module by pressing the "0" key while the DDT screen "number 33" is displayed.
Pressing the "ENTER" key, while DDT screen "number 33" is displayed will change the choke trim screen to display the following:
"CHOKE TRIM"
"00 00/00 kPa 33<"
The numbers on the second line are: Choke trim offset, Actual Inlet Manifold Pressure (kPaa)/Desired Inlet Manifold Pressure (kPaa).
Note: A change in the fuel consumption due to a change in the engine stability (misfire), will change the DESIRED manifold pressure.
As described above, the actual inlet manifold pressure can be changed from this screen by the use of the "ALT1" and the "ALT2" keys in order to adjust the position of the choke plate.
Pressing the "ENTER" key while the DDT screen "number 33" is displayed will return the choke trim screen to display the Actual Inlet Manifold Pressure and the Engine rpm.
Note: To prevent zeroing out any adjustments that have been made, always use the "SELECT MODE" key in order to exit the screen "number 33" .
Mechanical Choke Trim Procedure
The inlet manifold pressure can be adjusted by changing the length of the connecting rod linkage between the choke actuator and the choke plate. Refer to the Specifications Manual for the choke linkage setting specifications.
- Set engine operating condition to the rated speed and no load (or minimum load possible).
- Loosen the jam nuts on the linkage rod that connects the choke actuator to the choke plate. This connecting rod has LH and RH threads on the opposite ends.
- To change the inlet manifold pressure, adjust the length of the linkage rod.
Note: Increasing the length of the connection may disengage the connecting rod from the rod end assembly.
This process should be done slowly. Pause after every adjustment in order to allow the engine to respond to the change in the inlet manifold pressure.
Monitor the following:
- inlet manifold pressure
- stability of the engine rpm
- position of choke actuator
- position of wastegate actuator
- individual cylinder combustion burn times
- individual cylinder exhaust port temperatures
- inlet manifold pressure
- After completion of the choke trim process, tighten the jam nuts on the linkage rod.
- Confirm that all the cylinders are firing by checking the combustion burn times for the cylinders (screen "number 14" on the DDT). A combustion burn time greater than 10 ms will indicate that the cylinder is misfiring. Also, check the cylinders for low exhaust port temperatures. If engine stability is unacceptable after properly completing the choke trim procedure, refer to the Testing and Adjusting, "Governor Adjustment Procedure" of this manual.
Air Lines (Choke)
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| Illustration 1 | g00484068 |
(1) Aftercooler inlet line. (2) Adjusting bolt. (3) Housing. (4) Air inlet from turbocharger. (5) Cover assembly with adjusting bolt and locking nut. (6) Lever and linkage. (7) Adjustable rod. (8) Actuator. (9) Inlet port. (10) Outlet port. (11) Shaft. (12) Plate and mounting bolts. (13) Thrust washer. | |
Assemble the choke and the actuator linkage according to the following procedure:
- While the housing (3) is removed from the engine, install the shaft (11) in the housing.
- Assemble the plate (12) to the shaft (11) . Leave the mounting bolts for the plate loose.
- Install the cover assembly (5) and the thrust washer (13) .
Tighten the mounting bolts for the thrust washer to the following torque. ... 47 ± 9 N·m (35 ± 7 lb ft)
- Hold the plate in the fully closed position while tightening the mounting bolts for the plate.
Tighten the mounting bolts for the plate to the following torque. ... 12 ± 3 N·m (9 ± 2 lb ft)
- Install the assembled housing (3) and the gaskets on the engine.
- Install the plate and the housing. Hold the plate in the closed position. Tighten the adjusting bolt (2) until the adjusting bolt makes contact with the stop plate.
- Tighten the adjusting bolt for an additional 1/4 turn.
Tighten the locking nut to the following torque. ... 25 ± 6 N·m (18 ± 4 lb ft)
Note: Do not allow the adjusting bolt to turn while the locking nut is tightened.
- Install the lever and linkage (6) on the shaft.
 | |
| Illustration 2 | g00496202 |
(14) Rod end nuts. | |
Adjust the actuator linkage by using the following procedure.
- With the choke in the fully closed position, assemble the actuator lever at an angle (A) of 27 degrees from vertical.
- With the choke in the fully open position, the actuator lever should be at the angle (B) of 46.1 degrees from vertical.
- Tighten the rod end nuts (14) .
Tighten the rod end nuts to the following torque. ... 25 ± 6 N·m (18 ± 4 lb ft)
Correct adjustment and lubrication of the mechanical actuator linkage should result in good engine operation over the entire speed/load range of the engine. If no load instability is encountered, and the mechanical linkage is adjusted correctly, the Digital Diagnostic Tool can be used to electronically fine tune the actuator in order to improve the engine operation at no load conditions. Use the "TRIM" mode and the instructions that are included with the DDT in order to make the adjustments.