Usage:
3406 And 3408 Truck Engines
- SUPPLEMENT: 03/02/83
TRUCK ENGINE NEWS, DECEMBER 8, 1982, PAGE 8. In the article, "Improvements Made To Fuel Ratio Control," change the second sentence, in the third paragraph, under the topic "Description of Change" to read: "The new seal is made of a Viton material and causes less friction between itself and the housing. "
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Reference: Truck Engine News, March 17, 1982, Page 1. The article " New Diaphragm Used In Fuel Ratio Control" tells about the use of a new gray silicone diaphragm in the control group.
Description of Change: Several improvements have been made to the fuel ratio control groups to increase service life and improve performance (faster reaction time). These improvements include new valve assemblies, a lip-type seal, spring retainer, and an improved diaphragm. Also, a new strainer assembly is used in the governor group on 3406 Truck Engines
The two new valve assemblies have smoother bore surfaces for a better fit with the 2P8939 Valve. This smoother surface will improve performance.
A new lip-type seal is used with the new valve assemblies. The new seal is made of a Viton material and causes less friction between itself and the valve assembly. Formerly, two seals were used. These seals have worn the housing in some applications.
The new spring retainer is made from stamped metal. It must be installed with the convex side toward the air chamber. If the new spring retainer is not installed correctly, the fuel ratio control will not work correctly.
Illustration 1. Location of new parts in fuel ratio control group.
An improved diaphragm is now used. This diaphragm now has a rib (bead) around the inside diameter to make a better seal around the retainer assembly. This will prevent leakage of oil into the air chamber. The part number of the diaphragm did not change, but for identification purposes the color was changed to white. The former diaphragm was gray in color.
The new strainer assembly is used in 3406 Truck Engines. The new strainer assembly has a smaller orifice which slows (restricts) the flow of oil to the fuel ratio control. This permits slower action of the fuel ratio control in relation to sudden changes in boost, and more time to change gears without a loss of power. The smaller orifice in the new strainer assembly will not decrease normal acceleration of the engine.
Adaptable As: The new parts are direct replacements for the former parts as shown in Chart A. All the parts, except the 2W8449 Strainer, are in effect with 3406 Truck Engine Serial Number 92U61541 and 3408 Truck Engine Serial Number 28V4539. An in effect serial number for the use of the strainer is not available at this time.
It is our recommendation to put an "N" mark on any fuel ratio controls that have had all the new parts installed. This "N" mark will make it easier in the future to tell which fuel ratio controls have the new parts. An "N" mark can also be put on the governor housing when the new strainer is installed. See Illustration 2. Also, when any of the parts in the fuel ratio control are changed, the fuel ratio control must be adjusted according to the procedure in the Service Manual.
Illustration 2. Location of strainer assembly in the governor group.
General Information
Springs
To make identification of the springs in the fuel ratio control easier, they have color codes (marks) on them. The springs currently used and their color codes are shown in Chart B. See the Parts Books for the part numbers of the spring used in your application.
Valve Assembly
There has been a problem with burrs on some of the former valve assemblies. These burrs can cause a restriction in the movement of the valve assemblies.
To check the operation of the valve assembly and the internal valve, the internal valve must be moved in the same direction as it moves when installed on the engine, towards the governor. If the operation is checked by movement of the internal valve in the opposite direction, the indication will be that the valve does not operate correctly even if the valve is in good condition. This is because of the sharp edges of the oil groove, not a burr.
Some servicemen have at times ground the ends of the 2P8939 Valve (internal) to try to improve the alignment of the opening in the internal valve with the holes in the valve assembly. This modification is not necessary, because the holes do not control the amount of oil that will drain. The groove in the valve assembly controls the amount of oil. Any improvement in performance after this modification was probably from the use of a new diaphragm, seals or adjustments.
Also, reports show that the letters "PC" on the end of the 2P8802 Valve Assemblies have caused some confusion (problems). These letters are for identification purposes only. They do not mean that the valve assembly must be used only in a precombustion chambered engine. The 2P8802 Valve Assemblies with the letters "PC" are correctly used in several direct injection engines. If de sired, the "PC" mark can be removed from the end of the valve assemblies to prevent any confusion in the future.
Diaphragm
Formerly, the 2P8804 (Black) and 1W4797 (Gray) Diaphragms were used. The former black diaphragm can become rigid and possibly crack. This can cause a loss of boost and slow action of the fuel ratio control. The former gray diaphragm has been found with oil in the air chamber. This was caused by leakage around the retainer assembly. This small amount of oil leakage will not decrease engine performance, unless it is the result of a damaged diaphragm.
Tests For Fuel Ratio Control
The diaphragm, covers and gaskets can be checked for air leakage and the fuel ratio control can be checked for correct movement while the fuel ratio control group is still on the machine. To make these checks, it will be necessary to fabricate a tool group as shown in Illustration 3. To check the diaphragm, covers and gaskets for air leakage, use the procedure which follows.
NOTE:
The engine can be stopped or running for these checks.
1. Disconnect the boost (air) line for the fuel ratio control at the fuel ratio control.
2. Connect the tool group to the fuel ratio control.
3. With the use of the regulator, put approximately 70 kPa (10 psi) of air into the fuel ratio control. Close both of the valves. The air pressure to the fuel ratio control must never be more than 205 kPa (30 psi).
4. If the air pressure does not change, there are no leaks in the fuel ratio control. If the air pressure decreases in a short period of time, go to the next step.
5. Make a soap and water solution. Put this solution on the fuel ratio control while the pressure is kept at 70 kPa (10 psi). Check for bubbles. This can be an indication of a leak. If there are no bubbles the leakage is probably in the diaphragm.
Movement of the fuel ratio control can be checked only while the engine is running. To do this, use the procedure which follows.
1. Install the 9S240 Rack Position Tool Group.
2. The fabricated tool group must be connected to the fuel ratio control. Then let 35 kPa (5 psi) of air for approximately 10 to 15 seconds into the fuel ratio control. This will put the fuel ratio control in the operate (cocked) position. Release the air pressure.
3. Rapidly increase and decrease the engine rpm. The dial indicator will show changes in rack travel. The indications will gradually increase, stop, and then decrease. The point at which the indications stop before they start to decrease, is the setting of the fuel ratio control. To correctly check the fuel ratio control setting, there must be no air pressure in the fuel ratio control and it must be in the operate position.
4. The indicator in the rack position group can now be used to check movement of the valve assembly in the fuel ratio control. After the fuel ratio control has been cocked, the indicator will show changes of the valve assembly position in relation to increases in air pressure. Approximately 0.51 mm to 0.66 mm (.020 " to .026") of movement will be seen for every 7 kPa (1 psi) change in air pressure.
Illustration 3. Parts needed for fabricated tool group.