Hummer H1 (2002+). Manual — part 11

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Engine 2-5

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05745159

ROAD TESTING

The purpose of road testing is basically to confirm or deny the
existence of an engine fault. Procedure is as follows:

1.

Note condition of wheels/tires before test. Worn, damaged
tires or wheels can cause vibration or noise.

2.

Check and adjust lube levels in engine and transmission
and top off engine coolant if necessary.

3.

Turn off A/C system.

4.

Start and run engine at idle speed with transmission in
neutral. Record any noise or vibration that may be present.
ÒRevÓ engine and note any noise/vibration plus any
change in magnitude or frequency.

5.

Drive vehicle at legal speed and note any evidence of
noise, vibration, low power, miss, etc.

a.

If vibration was noted, drive vehicle above vibration
speed. Then shift into neutral and coast down through
problem range. If vibration still occurs, problem is
with chassis component. However, if vibration ceases,
problem is with driveline component.

b.

If noise is noted, shift into neutral at about 35 mph
and note if noise changes in pitch, frequency, or stops
altogether.

6.

Operate A/C system and note effect. If noise or vibration
begins, problem is related to A/C compressor, clutch,
accessory mounting bracket, or belt. However, if noise/
vibration is absent, note this and proceed to next step.

7.

Connect compound gauge to manifold air intake tube
fitting. Then press accelerator pedal to wide open position
and record boost reading which should be 2 psi or greater.

ENGINE NOISE DIAGNOSIS

Engine noises are usually sensitive to changes in rpm and load.
For example, a collapsed lifter will make an audible ÒtickingÓ
noise that increases in frequency as rpm goes up.

Engine noises can also be determined according to speed of the
related rotating component. For instance, valvetrain noises will
be at a frequency that is one half crankshaft speed.

Accessories

Noise caused by engine accessories such as the vacuum pump
alternator, power steering pump, A/C clutch, or drive pulleys is
speed sensitive. An increase or decrease in engine rpm will
generally change pitch and frequency, or even cause it to stop.
A mechanics stethoscope will generally help pinpoint a noise
source. Removing the accessory drivebelt will also help verify
an accessory generated noise.

Bearings

Bearing noise can be differentiated by pitch. A damaged con-
necting rod bearing makes a higher pitched, metallic knocking
sound. This as opposed to the lower pitch thump of a worn, or
spun main bearing. A failed rod bearing can be confusing as it

seems to make a greater frequency noise. This is because the
bearing may knock at both ends of piston travel.

Piston and Connecting Rod

Piston slap is usually caused by severely worn cylinder bores
and pistons, partially collapsed piston skirts, worn pin bores,
severely worn rings, or an undersized piston. An incorrectly as-
sembled, or installed connecting rod and piston assembly will
also produce slap.

Slap always occurs at crankshaft speeds. In severe cases, slap
may occur in both directions of piston travel. Although fairly
common on high mileage engines, slap can be difficult to hear
on low mileage engines. As the term implies, piston slap is ap-
propriate for the sound generated. It occurs when a piston be-
gins to rock within the cylinder as it travels up and down. This
action causes the skirt to slap the cylinder wall as it straightens,
then rocks away from the direction of thrust.

Valvetrain and Camshaft

Rocker arm and hydraulic lifter noise is probably the most eas-
ily identifiable. Both make tapping (or clicking) noises that
only differ in pitch and volume. Although damaged valve
springs or pushrods are more difficult to hear, they usually
cause a power loss or rough engine condition and require in-
spection to locate.

A worn, missing, or incorrect thickness camshaft thrust washer
will cause excessive cam end play. The most frequent result is
an audible knocking sound localized at the rear of the block.

Timing gear and chain noise is not always audible, even when
the chain and gears are severely worn. These components,
when failed, are usually discovered during timing checks
prompted by a low power or no-start condition.

NOTE:

Valvetrain noise can also be the result (or first indica-

tor) of low oil pressure.

Starter Noise

The starter bendix can hang and prevent quick disengagement
after startup. The resulting noise can be misdiagnosed as en-
gine related. A mechanics stethoscope is fairly effective at dif-
ferentiating engine and starter noise.

Knocking Noise At Idle

Knocking noises can be from connecting rod bearings, a
cracked flywheel, converter touching the housing or cover, A/
C compressor, or loose exhaust component.

Look for exhaust components grounding against the body,
frame, or driveline component. Remove the converter access
cover and visually inspect the flywheel and converter. Check
the cover and converter housing for signs of contact. A fly-
wheel cracked at the hub will allow the converter to wobble
slightly. Test the A/C system for incorrect charge levels which
can produce compressor knock.

2-6

Engine

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Diesel Fuel Knock or Rattle

The rattling sound unique to diesel engine is normal. It is a
function of high compression ratio, injector nozzle spray pat-
tern and pressure, and compression ignition. However, incor-
rect injection pump timing, low quality fuel, or injector nozzle
faults can make the normal sound much more pronounced. If
the normal rattling is accompanied by, or becomes a knocking
sound, the fuel injectors, injection pump, pump timing, and
fuel quality must all be tested.

DIAGNOSIS EQUIPMENT

Diagnosing engine mechanical problems can be performed
with normal shop equipment.

Compression testing with a good quality gauge will reveal con-
dition of the engine rings, pistons, cylinder bores, valves, and
guides.

Vacuum diaphragm operation is quickly tested with a hand op-
erated vacuum pump. These pumps are available from compa-
nies such as Kent-Moore, Snap-On, RobinAire and Lisle.

A digital or analog multimeter is used for many tasks such as
checking wire continuity, shorted-open circuits and compo-
nents, ground connections, battery condition, glow plug cur-
rent levels, and so on.

A tachometer is required for checking/setting idle speeds. On
diesel engines, an especially accurate tachometer is needed to
check cranking speeds of 100-180 rpm.

An oil pressure gauge is necessary in order to accurately test
engine oil pressure. The best gauges are mineral oil filled to
avoid indicator needle bounce. The gauge should have a dial
range up to 100 psi in 2 psi increments. Necessary adapters to
connect the gauge are available from either the gauge manufac-
turer, or Kent-Moore Tool Corp.

An all purpose dial indicator set such as J

Ð

8001, is also

needed. Accurate measurement of clearances, component
wear, chain deflection, and overhaul dimensional settings is
only possible with a dial indicator. A good quality vernier cali-
per and micrometer set are also needed to check part toler-
ances.

SCAN TOOL USE

The Tech 2 scan tool is primarily designed to test/interrogate
PCM/TCM circuits. The tool is extremely useful in locating
sensor, switch, or computer faults that affect engine perfor-
mance. However, the tool is not really designed to replace vac-
uum gauges, compression testers, multimeters, or 12 volt test
lamps.

GLOW PLUG OPERATION AND TESTING

The engine glow plugs are used to heat air entering the com-
bustion chamber. Heating the air results in improved cold tem-
perature starting and engine warm-up.

A total of eight glow plugs are used; one for each cylinder.
Each glow plug is threaded into a cylinder head port located

just below the injector nozzle (Figure 2-5). The tip of each plug
extends into a pre-chamber which concentrates the fuel/air
mixture prior to combustion.

The glow plugs are operated by a relay mounted on a bracket
attached to the right side intake manifold. The relay is in circuit
with the ignition switch and is energized only when the switch
is in the ÒstartÓ and ÒrunÓ positions.

Turning the ignition switch to the ÒstartÓ position allows cur-
rent to flow through the switch to the relay and the PCM. Once
energized, the PCM uses information from the coolant temper-
ature sensor and the intake air temperature sensor to determine
glow plug Òon timeÓ. The PCM commands the relay to allow
current to flow through it and to the individual glow plugs and
monitors each glow plug circuit voltage individually. If a glow
plug failure is detected, a DTC P0380 will be set.

GLOW PLUG TEST

1.

Check all glow plug connections. They should be tight and
corrosion free.

2.

Verify that engine temperature is at or below 95¡F (35¡C).

3.

Turn multimeter to amps or current flow setting.

4.

Check current at each glow plug (Figure 2-6). Place
ammeter clamp around glow plug wire. Current should be
13-14 amps.

5.

If current at glow plug is less than 13-14 amps, further
diagnosis is required. If current is zero check fuses and
circuit for shorts, grounds and opens. Check the fusible
link between the starter and the glow plug relay.

Figure 2-5: Glow Plug Location In Cylinder

Head and Pre-Chamber

CYLINDER

FUEL

GLOW

PRE-CHAMBER

COMBUSTION

PISTON

BLOCK

VALVE

CHAMBER

PLUG

INJECTOR

HEAD

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Engine 2-7

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05745159

Figure 2-6: Checking Current at Each Glow Plug

OIL PUMP PRESSURE TEST

Connect the pressure test gauge to the transmitter fitting in the
valley of the block. Pressure should be a minimum of 6 psi (41
kPa) at hot idle and increase to 30 psi (207 kPa) at 2000 rpm.
Low pressures at both test ranges with correct oil level indi-
cate:

¥

Pump pickup strainer or tube loose

¥

Pump pressure relief valve or spring problem

¥

Pump gears worn, chipped

¥

Pump shaft worn, slipping

¥

Oil galley plug loose, missing

¥

Main bearings severely worn

¥

Cam bearing turned (spun) or misaligned

ENGINE DIAGNOSIS

General Information

The diagnosis charts describe common faults that may occur.
Potential causes are listed in order of probability. Although the
charts list frequent causes for specific engine related problems,
they do not cover every possible cause. The charts are intended
to serve as guides only.

The diagnosis information in this section is aimed at solving
engine mechanical problems with normal shop diagnostic
equipment.

GLOW PLUGS LH

13-14

A

AMMETER

00-S02-001

#2

GLOW PLUGS RH

#8

#4

#6

#3

#5

#1

#7

PK

PP

BL

PP

PP

BL

PP

PK

WAIT

POWER TRAIN CONTROL MODULE

(PCM)

PK

BL

YL

BK

FUSE

TO

IGNITION

SWITCH

TO

IGNITION

SWITCH

LAMP

CONTROL

RELAY

CONTROL

FEEDBACK

SIGNAL

FUSIBLE

LINK

G1

TO

STARTER

POS. STUD

FUSE

GLOW PLUG

RELAY

2-8

Engine

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Engine Diagnosis

PROBLEM

POTENTIAL CAUSE

CORRECTION

Hard Starting

1.

InsufÞcient cranking speed (below 100 rpm
cold or 180 rpm hot).
Caused by:
¥ Low batteries
¥ Bad cable connections
¥ Serpentine belt or alternator problem

2.

Starter problem
¥ Poor connections
¥ Relay
¥ Solenoid
¥ Brushes
¥ Armature
¥ Starter drive damage

3.

InsufÞcient fuel to injectors, or start switch
has fault. Check run solenoid also.

4.

Water in fuel (Þlter indicator light NOT on).

5.

Glow plugs inoperative (most noticeable at
cold ambient temperatures).

6.

Air in fuel delivery lines.

7.

Fuel return lines restricted or tank vent inop-
erative.

8.

Air cleaner plugged (after extended off-road
operation).

9.

Injection pump timing or camshaft timing
may be off if pump, cam, or timing chain/
sprockets/gears were removed/replaced dur-
ing service.

10. Vehicle misfueled.

1. Check, repair cables or connections. Recharge bat-

teries if low. Replace batteries if shorted, sul-
phated, damaged. Replace belt or tensioner if
damaged. Test alternator output and repair or
replace if low.

2. Check/repair cable and solenoid connections if

needed. Check starter draw; overhaul if draw
exceeds 450-475 amps.

Remove and overhaul starter if brushes, starter

drive, or armature are faulty.

3. Check fuel volume at supply pump and injectors

while cranking engine. If volume is low, check for
restrictions in lines or at Þlter. If volume is OK,
check pressure at pumps and injectors and repair
as needed.

4. Drain off water at fuel Þlter draincock. Then crank

engine with draincock open for 5-10 seconds to
purge remaining water. If water continues to
appear in fuel coming out draincock, purge fuel
tank and lines, and refuel vehicle.

5. Check fuse and wiring harness to plugs. Correct

open or short as required. Refer to diagnosis in
Section 12 if required.

6. Check for loose fuel line connections at pump and

injectors. Correct if necessary then bleed any
remaining air at injectors.

7. Check return lines (from engine to tank) and cor-

rect restrictions, kinks, plugged lines. Make sure
tank vent is OK. Repair as necessary.

8. Remove and clean air intake components. Replace

Þlter element if plugged or restricted.

9. Check timing marks on pump and front cover. If

aligned, check marks on pump gears and cam
sprockets. Re-time if necessary.

10. Drain sample at Þlter draincock. Replace fuel load

if fuel contains gasoline, kerosene, fuel oil, or low
quality fuel.