Skytrak 6042 Service Manual User Manual download pdf (Page 215)

7.21

Model 6042 Legacy Origin 7/02

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

MT3160

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