Usage:
3306B And 3406B Truck Engines With New Scroll Fuel Systems (NSFS)
A new fuel ratio control group is used to improve the service life of 3306B and 3406B Truck Engines with New Scroll Fuel Systems (NSFS).
A different material, that is more resistant to tearing (rupture), is used in the diaphragm of the new fuel ratio control group. Other changes include new springs, with different spring rates, and a modified spring seat (7W1691 Washer) to provide better alignment of fuel ratio control components.
NOTE: The 7N9215 Stop and the 3S4701 Nut formerly included in all control groups, are now included only in the 7W2832 Fuel Ratio Control Group for use on CARB (California) approved engines.
A new 7W2015 Extension (see illustration) is used. The new extension has been heat treated for increased wear resistance and improved service life. Also the new 7W2829 Cover has an increased inside diameter to minimize failures caused by the diaphragm rubbing on the cover.
NOTE: Some wear between the internal valve assembly and the extension is normal. Replace the extension only when the wear exceeds .38 mm (.015 ").
The 7N9062 Housing has not changed. However, the seating surface for the diaphragm (see illustration) should be checked for sharp edges if the control group is disassembled. Some housings have a sharp edge that can damage the diaphragm at installation. The edge should be removed by light polishing before the housing is assembled.
Fuel ratio control group.
Test procedures, adjustments and operation of the fuel ratio control group are given in the Service Manual.
NOTE: Use the procedure given in the Service Manual, 3406B Truck Engine, Testing And Adjusting Section, to adjust the dynamic fuel ratio control setting correctly. All NSFS fuel ratio controls should be dynamically adjusted.
The new fuel ratio control groups are direct replacements for the former groups as shown in Chart A.
The new fuel ratio controls are in effect as shown in Chart B. For engines not shown in Chart B, check the identification tag attached to the control group, for the part number shown in Chart A.
Chart C shows the parts that are different between the new and former fuel ratio control groups.
NOTE: Unless a failure occurs there is no need to upgrade earlier controls with new components. If a failure does occur, use the diagnostic procedure given in the 3406B Truck Engine Service Manual to determine the cause of the failure. If new parts are needed to repair the fuel ratio control, all of the new parts shown in Chart C should be used together.
