Two spin-on type filters are used. The primary filter is mounted on the frame rail. The first in the fuel flow is a strainer, and the second is a filter. Although they are not marked as such, the threaded sleeves that accept the cartridges are different sizes to prevent mismatching. The primary filter has a 1 in. x 12 thread. The secondary filter has a 13/16 in. x 12 thread. The word "Primary" or "Secondary" is cast into the top of the respective adaptor. See Figure 24979 .
The spin-on filter cartridges consist of a shell, element, and gasket combined into a unitized replacement assembly. No separate springs or seats are required to support the filters. A fuel shutoff valve is installed on the outlet side of the secondary filter.
The fuel filter adaptors are retained to the block with two bolts each. Torque these bolts to 58-73 N m (43-54 lb ft).
The fuel filter system consists of the following:
As contaminants build up on the filter medium, a number of factors start to affect vehicle performance:
All of these conditions can lead to power loss and subsequent operator complaints of "low power" and "reduced vehicle fuel economy" caused by the need to downshift more frequently on grades.
To determine if replacement of fuel filter (spin-on) is necessary. See Figure 21720 .
Flowchart for Replacement of Fuel Filter (Spin-on)
To replace the filter, perform the following step:
To install the filter, perform the following steps:
Mechanical tightening of the fuel filters is not recommended, and may result in seal damage, cartridge damage, or both. Tighten the fuel filters by hand only.
Note: There is a fuel system shutoff valve on the discharge side of the secondary fuel filter. This check valve is designed to prevent loss of fuel prime at time of filter replacement.