Hummer H1 Service Manual page 178

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FUEL SYSTEM CONTAMINATION
Organic Contamination
Diesel fuel systems are susceptible to fungi and other micro-or-
ganism 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 loca-
tion 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 addi-
tives 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 hesi-
tation, 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 cli-
mates may result in stalling, poor starting when the engine is
hot, and may damage the fuel injection system.
5745159
Fuel, Emissions, and Exhaust
A quick check on fuel quality can be performed with tool
J–38641–B.
NOTE: The fuel quality hydrometer provides a general indica-
tion of fuel quality and should not be considered to be scientif-
ically 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 contami-
nants such as water or sediment. Check the odor of the sample
for the presence of gasoline or other foriegn 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 in-
dicator 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 spe-
cific 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:
Diesel No.
2
API
30-39
Gravity
3-41
Diesel No. Special
1 Tool
39-44 J–38641–B
4-1-00