Fuel Filter: Testing and Inspection
Refer to the maintenance schedules for the recommended fuel filter replacement intervals.
The gear supply pump located in the back of the high pressure pump draws fuel from the fuel tank, through the fuel filter and into the high pressure pump. Restricted fuel filters may cause hard starting, no starting, and or white smoke.
Testing The Filter For Restrictions
NOTE: There can not be any visible signs of fuel leakage at the filter outlet line or fitting during testing. If a fuel leak is detected, STOP testing, remove special tool fitting #9745, and replace both fuel line washer seals.
- Disconnect the fuel filter outlet line at the fuel filter housing.
- Install fitting, special tool #9745 in place of the fuel line bolt and tighten to 35 N.m (25 ft. lbs.).
- Connect pressure/vacuum gauge #6828 to the fitting.
- Prime the fuel filter to remove any entrained air.
- Start the engine and allow to idle.
- Monitor and record the vacuum reading on the gauge for 30 seconds.
- Raise the engine rpm to 1500 rpm and monitor and record the vacuum reading on the gauge for 30 seconds.
The vacuum on the gauge should not exceed 10 in. H.g at idle, and throughout the entire rpm range. If the vacuum reading is higher than 10 in. Hg, inspect the low pressure fuel system for restrictions such as, kinked lines or collapsed hoses, before replacing the fuel filter.
Remove special tools, install the fuel filter outlet line using the fuel line bolt with two new washer seals. Tighten the fuel line bolt to 35 N.m (25 ft. lbs.).
Prime fuel system, start the engine, allow to warm, turn engine off and inspect for leaks at the fuel filter and housing.
INJECTOR LEAK QUANTITY
WARNING: REVIEW THE HIGH PRESSURE FUEL SYSTEM WARNING BEFORE BEGINNING SERVICE.
NOTE: If an injector is found to be out of specification, repeat the test procedure after the injector replacement. Hydraulic flow will take the path of
least resistance and multiple failures may be identified.
Perform this test with the engine at operating temperature. This test will assist in determining a defective or internally leaking injector(s) is present by measuring the amount of fuel return.
Cranking Test
1. Turn the ignition off.
2. Remove the engine cover.
NOTE: DO NOT remove the return fuel line clips retaining the return line to the injector. Push IN on the clip to release the hose and then again to install the test vials.
3. Disconnect the return fuel hose at the top of each of the injectors.
NOTE: Care must be taken not to damage the return line check valve between cylinder number four injector and the fuel rail.
4. Block off the disconnected return fuel hose before the fuel return junction on the left rear of the cylinder head cover.
5. Disconnect the camshaft position sensor (CMP).
NOTE: Attach special tool adaptor #9686 to the #4 injector and fill with clean diesel fuel to purge the air from the adaptor, then install the test vial onto the adaptor.
6. Install the test vials onto the injectors and secure with the return hose clips.
7. Crank the engine for ten seconds while monitoring each inner test vial.
8. Evaluate the individual return quantities.
The maximum permissible difference between the return quantity of the individual injectors and the injector with the highest return quantity is 3 graduation marks in the small vial.
EXAMPLE
Evaluation Injector #1 has excessive fuel return quantity, replace the injector. Injectors #2, #3, #4 are OK.
9. Perform the cranking test after the repair to assure no other injectors are identified.
Engine Running
1. Start the engine with the test vials in place.
2. Run the engine until the top mark on one of the large graduated vials is obtained.
3. Turn engine off immediately.
4. Evaluate the individual return quantities.
The maximum permissible difference between return quantities of the individual injectors, and the injector with the highest return quantity, is 3 graduation marks.
EXAMPLE
Evaluation Injector #1 has excessive return quantity, replace the injector. Injectors #2, #3, #4 are OK.
5. Perform the running test again after the repair to assure no other injectors are identified.
If the injectors pass the quantity test, continue with the diagnostic manual.