Hummer H1 (2006+). Manual - part 25

2-6

Engine

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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. “Rev”
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 drive-
line 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. 

ENGINE NOISE DIAGNOSIS

Engine noises are usually sensitive to changes in rpm and load. For example, a collapsed lifter will make an audible “ticking” 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, valve train 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 me-
chanics stethoscope will generally help pinpoint a noise source. Removing the accessory drive belt will also help verify an acces-
sory generated noise.

Bearings

Bearing noise can be differentiated by pitch. A damaged connecting 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 assembled 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 com-
mon on high mileage engines, slap can be difficult to hear on low mileage engines. As the term implies, piston slap is appropriate
for the sound generated. It occurs when a piston begins 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.

Valve Train and Camshaft

Rocker arm and hydraulic lifter noise is probably the most easily identifiable. Both make tapping (or clicking) noises that only dif-
fer 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 inspection 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.

NOTE: Valve train noise can also be the result (or first indicator) of low oil pressure.

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Starter Noise

The starter bendix can hang and prevent quick disengagement after startup. The resulting noise can be misdiagnosed as engine re-
lated. A mechanics stethoscope is fairly effective at differentiating 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 compres-
sor, 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 flywheel 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.

Diesel Fuel Knock or Rattle

The rattling sound unique to a diesel engine is normal. It is a function of high compression ratio, injector nozzle spray pattern and
pressure and compression ignition. However, low quality fuel or injector nozzle faults can make the normal sound much more pro-
nounced. If the normal rattling is accompanied by or becomes a knocking sound, the fuel injectors, injection pump 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 condition of the engine rings, pistons, cylinder bores, valves, and
guides.

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

A 10 mega-ohm impedance digital multimeter is used for many tasks such as checking wire continuity, shorted-open circuits and
components, ground connections, battery condition, glow plug current levels and so on.

An oil pressure gauge is necessary in order to accurately test engine oil pressure. The best gauges are mineral oil filled to avoid in-
dicator 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 manufacturer, or Kent-Moore Tool Corp.

An all purpose dial indicator set such as J

–

8001, is also needed. Accurate measurement of clearances, component wear, chain de-

flection and overhaul dimensional settings is only possible with a dial indicator. A good quality vernier caliper and micrometer set
are also needed to check part tolerances.

SCAN TOOL USE

The Tech 2 scan tool is primarily designed to test/interrogate ECM/TCM circuits. The tool is extremely useful in locating sensor,
switch, or computer faults that affect engine performance. However, the tool is not really designed to replace vacuum gauges, com-
pression testers, multimeters or 12 volt test lamps.

GLOW PLUG OPERATION

In the diesel engine, air alone is compressed in the cylinder. Then, after the air has been compressed, a charge of fuel is sprayed
into the cylinder and ignition occurs, due to the heat of compression. Eight glow plugs are used as an aid to starting. Control of the
instant start system (ISS) glow plugs is accomplished by an electronic glow plug control unit and 4.7 volt glow plugs, requiring
2þseconds to heat up to 1,000°C (1,832°F). The temperature and the power consumption is controlled between the engine control
module (ECM) and the controller within a wide range to suit the engine's pre-heating requirements. Each glow plug is energized in-
dividually. This capability yields more optimum heat times for the glow plugs, thus pre-glow times can be kept to a minimum for
short wait to crank times and maximum glow plug durability.

A NORMAL FUNCTIONING SYSTEM OPERATES AS FOLLOWS:

•     Turn the ignition ON with the engine OFF and at room temperature. 

2-8

Engine

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• 

The glow plugs turn ON and heat up in 2þseconds and then are pulse-width modulated (PWM) for another 2þseconds. 

• 

The glow plug wait lamp is ON for 1þsecond. 

• 

If the engine is cranked during or after the above sequence, the glow plugs may cycle ON and OFF after the ignition switch is 
returned from the start position, whether the engine starts or not. The engine does not have to be running to terminate the glow 
plug cycling. 

The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

The ECM provides glow plug operation after starting a cold engine. This post-start operation is initiated when the ignition switch is
returned to Run, from the Start position. This function helps clean up excessive white smoke and/or poor idle quality after starting.

GLOW PLUGS

The glow plugs are 4.7 volt heaters in each of the cylinders that turn ON, then pulse-width modulated when the ignition switch is
turned to the RUN position prior to starting the engine. They remain pulsing a short time after starting, then they are turned OFF. A
Wait to Start lamp on the instrument panel provides information on engine starting conditions. The Wait to Start lamp will not illu-
minate during post-start glow plug operation.

GLOW PLUG/CONTROLLER

The glow plug controller is a solid state device which operates the glow plugs. The glow plug controller is connected to the follow-
ing circuits: 

• 

The fuel heater ignitionþ1 voltage circuit 

• 

The battery voltage circuit 

• 

The CAN communication circuit located between the engine control module (ECM) and the glow plug controller 

• 

The engine ground circuit 

• 

The glow plug supply voltage circuits located between the glow plug controller and the glow plugs. 

The glow plug diagnostic circuits are directly monitored individually by using a separate transistor to control current to each glow
plug. Individual diagnosis is thus possible for every glow plug (Figure  2-4).

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Figure 2-4:   Checking Current at Each Glow Plug