Warning – SkyTrak 8042 Service Manual User Manual
Page 348
7A.25
Model 8042, 10042, 10054 Legacy
Rev. 10/03
Engine: Cummins 4BT3.9 and 4BTA3.9
a. Locating Faulty Fuel Injectors
A faulty fuel injector can cause:
• Misfiring
• Knocking
• Overheating
• Loss of power
• Smoky (black) exhaust
• Increased fuel consumption
The particular faulty fuel injector(s) may be determined by
releasing the pipe union nut on each fuel injector in turn,
with the engine running at a fast “tick-over.” If, after
slackening a pipe union nut, the engine revolutions
remain constant, a faulty fuel injector has been identified.
To test a fuel injector:
1. Remove the fuel injector (7) from the cylinder head.
Refer to Section 7A.8.7, b. “Injector Replacement.”
2. Invert the fuel injector, with the nozzle facing out,
then retighten the unions.
3. Loosen the unions of the other fuel injector pipes (to
help avoid the possibility of the engine starting).
4. Operate the starter to turn the engine over until fuel
sprays from the nozzle. Examine the shape of the
spray. If the spray is unduly “wet” or “streaky”, or
obviously sprays to one side, or if the nozzle
“dribbles” fuel, it may only be necessary to probe the
nozzle holes to remove blockage.
IMPORTANT: DO NOT attempt to adjust injection
pressure without a testing pump and pressure gauge. It
is not possible to accurately adjust the setting of fuel
injectors without the proper equipment.
A perfect fuel injector, when tested by pumping fuel through
it in the open air, gives a short “pinging” sound as the fuel
emerges from the holes. After the fuel injector has been
in service for some time, the pinging changes to a
crackling sound. It is not until the fuel injector sounds
“dead” that its condition is likely to affect the running of the
engine.
b. Injector Replacement
Preparatory steps:
1. Thoroughly clean around the injector(s).
2. Disconnect the high-pressure fuel lines (8).
3. Disconnect the fuel drain manifold (9).
WARNING:
Diesel fuel under pressure
can penetrate the skin and cause serious
personal injury. Slowly loosen fittings, and allow
release of residual pressure before removing.
MA1960
7
MT3160
8
9