Used lube oil analysis can identify a potential source of engine trouble before it occurs. A
program such as the Detroit Diesel Oil Analysis Program is recommended for monitoring crankcase oil in all engines. One of the most serious conditions used oil analysis can uncover is the presence of excessive fuel in the lube oil which should not exceed 2.5% maximum of oil volume, reference Detroit Diesel’s Publication 7SE270 “Engine Requirements for Lubricating Oil, Fuel and Filters.” While used oil analysis can uncover the presence of excessive fuel in the lube oil, other methods must be used to determine its source. A particularly effective test involves the use of special test fuel containing dye additives.

Prepare Test Fuel
The use of fluorescent dye(J–28431–B) is effective in fuel leak detection and should be the technician’s choice in preparing a test fuel mixture. However, if a “Black light“ or fluorescent dye are not available, red LTO 1140 may be substituted.
To prepare fluorescent dye (J–28431–B), mix 118 ml (four ounces) of fluorescent dye additive
with 15.1 liters (four gallons) of diesel fuel in a clean container marked with the words “Test Fuel”.
To prepare Red LTO 1140, mix 59 ml (two ounces) of Red LTO 1140 dye additive with 18.9 liters
(five gallons) of diesel fuel in a clean container marked with the words “Test Fuel”.
Fuel Leak Tests (E3 Injectors Installed/Engine Off)
To locate a leaking injector the tests below should be completed in the sequence indicated and stopped at a point when the leaking injector is diagnosed. If a leaking injector is found, do not
arbitrarily replace more than that injector, as multiple injector malfunctions are rare on the same engine.

During fuel pressure testing (engine off, 5 minutes at 345 kPa [50 psi]) fuel leakage will be evident at the injector body/plunger spring seat area see Figure 2-2. Factory tests have shown that accumulation of fuel at each injector, approximately a tablespoon may be evident during these tests. Evidence of fuel in this area is expected, as there is no other place for it to go when the injector cavities are pressurized, forcing fuel between the injector body and plunger.

Figure 2-2
Acceptable-Fuel Leakage Between injector Plunger and Body
Fuel Pressure Test
Since there is no known fuel leak tester available in the commercial market today, one must be
fabricated. Use the following guidelines to help in fabricating:
Although test fuel can be pressurized by variety of methods, Detroit Diesel recommends an air/fuel accumulator design capable of safely withstanding a minimum pressure of 345 kPa (50 psi).
The tester should have a capacity of 9.5 liters (2.5 gallons) of test fuel and provide for contamination free storage of the test fuel when not in use.
Regulated shop air may be used to charge the accumulator tank and maintain a constant test fuel pressure.
A shut-off valve should be installed at the accumulator outlet to start and stop pressurization during the test sequence.

Fuel Leak Tester

1. Fill fuel system tester with the fluorescent or red dye fuel mixture approximately 9.5
liters (2.5 gallons).

2. Charge tester (outlet valve closed) with shop air regulated at 345 kPa (50 psi).

3. Hook-up the tester to the engine fuel system. There are two options for fuel tester to engine hook-up as determined by the ease of access.
□ Option 1–Remove the fuel line from the outlet side of the fuel pump and connect the fuel system testers line in this fuel hose fitting. This hook-up location will require the fuel system shut-off valve to remain in the open position during testing. About 3.8 liters (1 gallon) of test fuel will be necessary to charge the engine’s fuel system from this hook-up location. Test fuel will not harm the engine’s fuel filters and may remain in the fuel system at the conclusion of testing.
□ Option 2–Remove the fuel line from the outlet side of the fuel by-pass filter adapter and connect the fuel testers line in this fuel hose fitting. It is recommended that the fuel system shut-off valve be placed in the closed position before removing the engine fuel line and remain closed until reinstalled. About 1.9 liter (0.5 gallon) of test fuel will be necessary to charge the engine’s fuel system from this hook-up location.

4. Remove rocker cover and disconnect the fuel outlet line at a convenient location between
the cylinder head and the fuel tank. Install an appropriate size pipe plug (loose) in the
fuel outlet line end and place it in a container to catch the fuel while priming the cylinder
head. If equipped, Jake Brakes® should be removed to allow for the visual examination
of the injectors during fuel leak testing.

5. Slowly open the fuel tester’s shut-off valve and charge the cylinder head fuel galley. When
test fuel is flowing from the fuel return line and air has been purged from the system, tighten the pipe plug at the engine fuel outlet line fitting.

6. With the fuel tester shut-off valve completely open and the cylinder head galley pressurized to 345 kPa (50 psi), visually monitor the overhead using a black light for five minutes if the test time goes beyond five minutes it will become more difficult to determine the faulty injector due to expected leakage at the injector plunger/body. Pay special attention to any leaks at the injector body, high and low pressure body plugs, see Figure 2-3and see Figure 2-5, injector nut to body and nut to tube seals see Figure 2-4, and stop valve cover see Figure 2-6.

Injector plunger/body leakage at the follower spring area is normal and expected during this test.

The figures that follow do not illustrate amount of fuel leakage but rather its origin or location. If injector(s) are removed and reinstalled in the head, the injector nut ‘O’ ring seals should be replaced with new parts.

7. Correct the cause of any abnormal fuel leaks.

8. Bleed the pressure from the accumulator tank and remove the pipe plug from the fuel outlet line. Reinstall the fuel outlet line in the engine’s fuel system. Disconnect the fuel tester and reinstall the fuel inlet line in the engine’s fuel system.

9. Completely open the engine’s fuel shut-off valve and assure that all fuel connections are tight. Reinstall the rocker cover and start engine to purge the air from the fuel system. If the engine fails to start, it may be necessary to prime the fuel system.

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