SkyTrak 6036 Service Manual - Manual (Page 199)

7.21 Model 6036 Legacy
Engine: Cummins 4BT3.9
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 inturn,
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 (Fig. 7-21, 1) from the
cylinder head (refer to Section 7.8.7, b. “Injector
Replacement.”)
Figure 7-21 Fuel Injector
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:
• Thoroughly clean around the injector(s).
• Disconnect the high-pressure fuel lines
(Fig. 7-22, 1).
• Disconnect the fuel drain manifold (Fig. 7-22, 2).
Figure 7-22 Fuel Injector Fuel Line and Drain Manifold
IMPORTANT: The injector must not rotate in the bore of
the cylinder head or damage to the cylinder head will
occur. If rust has formed on the hold-down nut, soak the
nut with rust-penetrating solvent for a minimum of three
minutes. Then, tap the injector body with a drift pin to
help loosen any rust.
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
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MT3160