Component Tests and General Diagnostics
FUEL SYSTEM CONTAMINATIONOrganic Contamination
Diesel fuel systems are susceptible to fungi and other micro-organism infestation when water is present. These fungi can grow into long strings or large globules anywhere in the fuel system. Due to the amount of water, the most prevalent location for fungi is the fuel tank.
The growths appear slimy and may be black, green, or brown. They are introduced by refueling with an unfiltered or aged fuel source.
Fungi feed on the fuel and need only trace amounts of minerals and water. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism.
The most common symptom is a loss of performance due to fuel filter clogging. Infestation can also show up as corrosion of metal parts such as injectors, fuel pumps, and steel lines.
WARNING: To avoid personal injury do not come into physical contact with biocide agents, cleaners, or additives used to remove fungi or micro-organisms.
If fungi have caused fuel system problems, sterilize the system with a diesel fuel system biocide or cleaning agent. Follow the manufacturer s instructions.
Use of biocides while operating under heavy loads such as towing a trailer is not recommended. Such use is permissible, but no additional biocide should be used when refueling during such operations.
Contamination that is severe or does not respond to biocides may require tank removal, disassembly, and steam-cleaning.
Water or Wax Contamination
1. Remove fuel cap from filler tube.
2. Drain fuel into portable tank with air powered pumping mechanism.
3. Drain filter, fuel pump, and fuel lines.
4. Refill tank with fresh fuel.
5. Start engine and bleed lines, filter, and injectors.
Checking Fuel Quality
The fuel quality may cause driveability problems such as hesitation, lack of power, stalling, the inability to start, etc.
For best results, use Diesel fuel No. 2 year-round (above and below freezing conditions) as the oil companies blend Diesel fuel No. 2 to address climatic differences. Diesel fuel No. 1 may be used in very cold temperatures ( when it stays below 0 °F (-18 °C); however; it will produce a loss in power and fuel economy.
CAUTION: The use of Diesel fuel No. 1 in warm or hot climates may result in stalling, poor starting when the engine is hot, and may damage the fuel injection system.
A quick check on fuel quality can be performed with tool J 38641 B.
NOTE: The fuel quality hydrometer provides a general indication of fuel quality and should not be considered to be scientifically accurate.
1. Drain the fuel filter housing as follows:
- Stop engine.
- Place container under drain valve hose at left front side of vehicle.
- Open drain valve.
- Start engine and run it at curb idle speed until clear fuel appears at drain valve exit hose.
- Fill a 1-liter (0.946 quart) container with sample of clean fuel.
- Close drain valve and stop engine.
NOTE: Visually inspect the fuel sample for obvious contaminants such as water or sediment. Check the odor of the sample for the presence of gasoline or other foreign solvents before testing for specific gravity.
2. Fill hydrometer tool J 38641-B with fuel sample as follows:
- Squeeze hydrometer bulb
- Immerse hydrometer tip in fuel sample
- Release bulb and allow fuel to enter glass tube until indicator floats freely.
- Gently spin hydrometer to relieve surface tension of fuel sample.
3. Read the scale on the glass bulb at the point where the top of the fuel sample contacts it:
- Reading this scale will indicate an approximate fuel oil specific gravity.
- Refer to tool instructions on how to determine API specific gravity.
- Refer to Fuel Oil Specific Gravity Requirements table.
4. If the correct fuel is being used in the conditions listed in Fuel Quality (below) and meets the fuel oil specific gravity requirements for Diesel No. 1 or Diesel No. 2, the fuel is OK. If not, the fuel should be replaced.
Fuel Oil Specific Gravity Requirements:
