0334833 JOHNSON PLUG

Illustration 1 g00578151
2P-8278 Fuel Flow Tube (Sight Gauge) (1) A steady stream of small bubbles with a diameter of approximately 0.1588 cm (0.0625 inch) is an acceptable amount of air in the fuel. (2) Bubbles with a diameter of approximately 0.635 cm (0.25 inch) are also acceptable if there is two seconds to three seconds intervals between bubbles. (3) Excessive air bubbles in the fuel are not acceptable.
If excessive air is seen in the sight tube in the fuel return line, install a second sight tube at the inlet to the fuel transfer pump. If a second sight tube is not available, move the sight tube from the fuel return line and install the sight tube at the inlet to the fuel transfer pump. Observe the fuel flow during engine cranking. Look for air bubbles in the fuel. If the engine starts, check for air in the fuel at varying engine speeds. When possible, operate the engine under a load and look for air in the fuel.If excessive air is not seen at the inlet to the fuel transfer pump, the air is entering the system after the fuel transfer pump. Proceed to Step 5.
To avoid personal injury, always wear eye and face protection when using pressurized air.
To avoid damage, do not use more than 55 kPa (8 psi) to pressurize the fuel tank.
Pressurize the fuel tank to 35 kPa (5 psi). Do not use more than 55 kPa (8 psi) in order to avoid damage to the fuel tank. Check for leaks in the fuel lines between the fuel tank and the fuel transfer pump. Repair any leaks that are found. Check the fuel pressure in order to ensure that the fuel transfer pump is operating properly. For information about checking the fuel pressure, see Testing and Adjusting, "Fuel System Pressure - Test".
Proceed to Step 6 if an infrared thermometer or an exhaust temperature pyrometer is not available. Start the following procedure with a cold engine. Take all measurements within the first five minutes of operation. The temperatures of the exhaust manifold ports should be within 20 °C (68 °F). An exhaust port that has a low temperature may have an injector that is leaking air.
Start the engine and operate the engine at low idle.
Measure the temperature at the center of the number one exhaust manifold port and at the center of the number six exhaust manifold port. Compare the two temperatures.
Measure the temperature of the number two exhaust manifold port and the number five exhaust manifold port. Compare the two temperatures.
Measure the temperature of the number three exhaust manifold port and the number four exhaust manifold port. Compare the two temperatures.Note: Injectors that are downstream from a leaking injector may measure cold but not leaking air.
Remove the valve cover and operate the engine at low idle rpm.
Illustration 2 g00598910
(1) Fuel injector rack (2) Fuel-on position
Check each cylinder sequentially from the number six cylinder to the number one cylinder. Use a screwdriver to move each fuel injector rack (1) to the fuel-on position. Watch the sight tube in the fuel return line. An increase in the amount of air in the fuel indicates that the injector is leaking air. Also note the amount of increase in fuel injector rack that is required to cause a cylinder to knock. An injector that is leaking air will require the fuel rack to be advanced more toward the fuel-on position. If the source of air can be isolated to a particular injector, remove the injector. Ream the injector sleeve if the seat area for the injector is pitted. Replace the injector sleeve, if necessary. Reinstall the injector. Ensure that the injector is properly seated. Refer to Tool Operating Manual, NEHS0738, "Using the Injector Seating Tool " and Tool Operating Manual, NEHS0610, "Using the 128-8822 Tool Group on 3114, 3116, and 3126 Engines with Mechanical Unit Injectors (MUI)". Also, refer to Video Tape, LEVN4032, "Troubleshooting Guide for the 3100 Family of Diesel Engines" and Video Tape, LEVN4732, "Injector Seating Procedure". After the injector is reinstalled, check for air in the fuel.
If the source of air can not be isolated to a particular cylinder, remove each injector. Ream all injector sleeves or replace all injector sleeves. Replace an injector only if the injector cone is damaged. A burned O-ring or a missing O-ring on the end of the injector does not indicate a faulty seal. The O-ring should not be replaced.