SkyTrak 6036 Service Manual - Manual (Page 140)

Section 8B Cummins Engine
8B-20 Model 6036/6036T S/N 9B0500 thru 14833
Failure of the needle valve to lift and close at the
correct time or needle valve stuck open can cause
the engine to misfire and produce low power. Fuel
leaking from the open nozzle can cause a fuel
knock, poor performance, smoke, poor fuel
economy, and rough running.
a. How to Locate Faulty Fuel Injector(s)
A faulty fuel injector can cause:
• Misfiring
• Knocking in one (or more) cylinders
• Engine overheating
• Loss of power
• Smoky exhaust (black)
• Increased fuel consumption
The particular faulty fuel injector or fuel injectors
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, this denotes a faulty fuel injector.
To test the fuel injector:
1. Remove the fuel injector from the cylinder
head.
2. Invert the fuel injector with the nozzle facing
outwards and then retighten the unions.
3. Slacken the unions of the other fuel injector
pipes (to avoid the possibility of engine start-
ing).
4. Use 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 to one side, or if the
nozzle “dribbles” it may only be necessary to
probe the nozzle holes to remove carbon.
Be careful to keep hands and face from coming
in contact with spray as it will cause fuel oil to
penetrate the skin.
IMPORTANT: Do not attempt to adjust injection
pressure without a testing pump and pressure
gauge. It is impossible to adjust the setting of fuel
injectors with any degree of accuracy 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 con-
dition is likely to affect the running of the engine.
b. Injector Replacement (Fig. 8B.42)
Preparatory Steps:
• Thoroughly clean around the injectors.
• Disconnect the high pressure fuel lines.
• Disconnect the fuel drain manifold.
IMPORTANT: The injector must not rotate in the
bore of the cylinder head. This will damage the
cylinder head. If rust has formed on the hold down
nut, soak the hold down nut with a rust penetrating
solvent for a minimum of 3 minutes and hit the
injector body with a drift pin to loosen any rust.
1. Hold the injector body with a 16 mm wrench
while you loosen the hold-down nut with a
24 mm box end wrench.
2. Clean the injector nozzle bore.
3. Remove the injector hold-down nut from the
injector body.
4. Apply a coat of anti-seize compound to the
new injector surface, avoid getting the anti-
seize compound in the fuel drain hole.
5. Install the hold-down nut on the injector body.
6. Install a new o-ring into the recessed groove in
the top of the hold-down nut. Make sure the o-
ring is not cut or twisted when installing.
7. Apply a coat of anti-seize compound to the
threads of the injector hold-down nut.
8. Assemble the injector and new copper washer,
use only one copper washer. Place a light
coat of clean 15W40 engine oil between the
washer and injector to help keep the washer
from falling during installation.
9. Install the injector with the protrusion on the
side of the nozzle fitting into the notch in the
head.
10. Tighten the hold-down nut and torque to
44 lb-ft (60 Nm).
11. Install the fuel drain manifold and torque to
Warning