1986/12/22 Caterpillar

3406B Engines

Reports indicate that some dealers may be using inaccurate test procedures when troubleshooting for fuel dilution of the lube oil. In some cases, the results of the tests performed may be misinterpreted. In other cases, the most likely causes are being overlooked. When troubleshooting for fuel dilution of the lube oil, use the procedures that follow in the sequence given.

A. Verify Fuel Dilution

B. Internal Fuel Lines

C. Fuel Injection Nozzles

D. Fuel Transfer Pump

E. Fuel Injection Pump Housing

Verify Fuel Dilution

Fuel dilution of the lube oil can be verified by two methods. First, by the test results of an S·O·S (Scheduled Oil Sampling). Second, by an increase in the oil level. If the second method is used, make sure the increase in the oil level is due to the addition of fuel.

Internal Fuel Lines

To test the internal fuel lines, it will be necessary to use the 5P4150 Nozzle Testing Group and two lengths of wire braided hose capable of withstanding a pressure of at least 20,700 kPa (3000 psi). Modify the two lengths of wire braided hose as follows:

1. Install a 6V3989 Nipple on one end of each hose. This end will be connected to the nozzle tester with a 6V4143 Coupler Assembly (Quick Disconnect).

2. Weld a section of fuel line and its nut to an appropriate fitting. Install this fitting on the end of one hose.

3. Weld an appropriate fitting to the bottom of a 2W3409 Fuel Pump Bonnet. Install this fitting on the end of the second hose.

Check for internal leaks as follows:

1. Remove both valve covers and valve cover bases.

2. Wipe off all internal fuel lines, fuel injection nozzles, and/or nozzle adapters.

3. Disconnect one end of an external fuel line. Disconnect the end that is easier to work with.

4. Use the appropriate hose to connect the 5P4150 Nozzle Testing Group to the external fuel line or to the fitting on the cylinder head fuel line adapter. This will make it possible to pressurize the internal fuel line and fuel injection nozzle.

5. Close the on-off valve, and open the isolation valve on the tester. Pump the handle rapidly until a pressure of 20,700 kPa (3000 psi) is obtained. Close the isolation valve.

6. Check for leaks at the areas shown in Illustrations 1 and 2.

Illustration 1. Location to check for internal fuel leaks with 1W2950 or 7W1902 Adapters.

Illustration 2. Locations to check for internal fuel leaks with 7W1645 Adapter.

7. Do Steps 3-6 for all the cylinders.

Fuel Injection Nozzles

To check the fuel injection nozzles for leaks, remove the nozzles from the engine. Do not remove the bleed screws. Apply a pressure of 20,700 kPa (3000 psi) to the nozzle with the 5P4150 Nozzle Testing Group. Check the nozzles for leaks in the areas shown in Illustration 3. Observe for 4 to 5 minutes. Small leaks are not readily apparent in the typical 1 to 2 minute check. It is recommended that all of the tests in Special Instruction, Form SEHS7292, be performed at this time.

Illustration 3. Locations to check for fuel injection nozzle leaks.

Fuel Transfer Pump

This test must be performed with the fuel and the fuel transfer pump at a temperature between 18° and 29°C (65° and 85°F). Check the fuel transfer pump for excessive leakage as follows:

1. Fill the pump with fuel, and plug the outlet port.

2. Connect a regulated air supply and a shutoff valve to the inlet port of the pump. Set the regulator so the pressure is 520 ± 35 kPa (75 ± 5 psi). Do not open the shutoff valve at this time.

3. Mount the pump in a vise with the tappet about 3° to 5° below horizontal. See Illustration 4.

4. Wipe off the pump and turn the air supply on. Make sure there are no leaks except from between the guide and tappet.

5. Wipe off the face of the guide again. Let a few drops of fuel fall off the guide before starting the count.

6. Count the number of drops of fuel that fall off the guide in one minute. The pump is good if six or less drops fall per minute.

Illustration 4. Location to check fuel transfer pump leakage.

Fuel Injection Pump Housing

This test must be performed with the fuel injection pump housing and the fuel at a temperature between 18° and 29°C (65° and 85°F). Test and inspect the fuel injection pump housing as follows.

1. Disconnect the fuel injection lines and the fuel return line from the pump. Cap all of the bonnets and the return line fitting, so they will not leak when pressure is applied. Fuel injection lines can be modified for capping the bonnets.

2. Disconnect the fuel supply lines, and make sure the pump housing is full of fuel. Connect a pressure gauge and shutoff valve to the supply fitting as shown in Illustration 5. Connect an air supply to the shutoff valve. Make sure the caps, connections, the shutoff valves and the gauge do not leak.

3. Apply 480 kPa (70 psi) air pressure to the pump housing. Close the shutoff valve.

4. Observe the pressure loss over a period of five minutes. A pump is good if the pressure loss in five minutes is 35 kPa (5 psi) or less.

5. If the pressure loss exceeds 35 kPa (5 psi) in five minutes, remove each of the injection pumps one at a time. Inspect the seal surfaces of the barrel, timing spacer, and housing. See Illustration 6. Check the surface finish of these parts. Make sure that none of these surfaces have any dirt, debris, nicks, cracks, or scratches on them.

6. Install all the injection pumps in the pump housing. Test the pump housing again for pressure loss.

Illustration 5. Test set up for fuel injection pump housing leak test.

Illustration 6. Locations to check for leakage.