Hummer H1 (2002+). Manual - part 36

 

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 Fuel, Emissions, and Exhaust  3-5

  

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5745159

 

Figure 3-7:   Electronic Accelerator Pedal 

Components

Figure 3-8:   Electronic Accelerator Pedal 

(Location)

Figure 3-9:   Accelerator Pedal Connector Clip

 

Electronic Fuel Injection Pump Operation

 

The electronic fuel injection pump is operated by the power-
train control module. The pump contains a fuel solenoid driver,
an optical and fuel temperature sensor, a shut off solenoid, a
stepper motor, and a fuel solenoid. Additional signal sources
that affect pump operation are: crankshaft position sensor,
boost sensor, coolant temperature sensor, intake air tempera-
ture sensor, and electronic accelerator pedal.

At initial engine start, the fuel/lift pump continuously supplies
fuel to the injection pump.

A change in accelerator pedal position to part throttle, causes
an equivalent change in pedal potentiometer voltage output.
The PCM then signals the solenoid driver to increase fuel flow.
Flow rates are further refined based on various signals from en-
gine sensors.

The boost/baro sensor monitors changes in intake manifold
pressure. Pressure changes are converted into a voltage signal
transmitted to the PCM. High voltage readings indicate high
manifold pressures and low voltage indicates low pressure.

The intake air temperature sensor monitors incoming air tem-
perature. Cold air generates high sensor resistance readings
while warm air generates lower readings. The resistance sig-
nals are transmitted to the PCM which richens or leans the fuel
mixture as needed.

Barometric pressure is monitored by the baro sensor. The sen-
sor signal is used by the PCM to adjust injection pump timing
and fuel mixture for different altitudes.

The stepper motor advances/retards injection timing on com-
mand by the PCM. Signals from the optical, air temperature,
crankshaft position, coolant temperature, and fuel temperature
sensors, are all utilized by the PCM to optimize settings.

Fuel injector cycles are monitored by the PCM (which controls
injection). The fuel solenoid driver returns a pulse width signal
to the PCM every time it seats the fuel solenoid. This signal in-
dicates injection has occurred at one of the injectors, and the
length of the injection cycle.

PEDAL AND ARM

BRACKET

POTENTIOMETER

MODULE

ACCELERATOR PEDAL

CONNECTOR

FRONT OF

VEHICLE

CONNECTOR

CLIP

 

3-6

Fuel, Emissions, and Exhaust

 

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POWERTRAIN CONTROL MODULE (PCM)

 

The PCM controls operation of all of the engine and transmis-
sion outputs. It is on a bracket attached to floor under the cen-
ter console. The data link connector is the access point for the
scan tool. The connector is under the instrument panel at the
left side of the steering column. It is a multi-pin connector with
integral mounting bracket.

Signal inputs used by the PCM include:

• Coolant temperature

• Intake air temperature

• Boost/baro pressure 

• Optical/fuel temperature sensor 

• Crankshaft position sensor 

• Accelerator pedal position sensors (APP)

• Cruise control

• A/C request

• Vehicle speed sensor

• Automatic transmission fluid pressure manual valve po-

sition switch

• Transmission input speed sensor

• Transfer case low range switch

• Transmission fluid temperature sensor

• Diagnostic request

 

FUEL SYSTEM DIAGNOSIS

General Information

 

Fuel system diagnosis should begin with a preliminary inspec-
tion followed by a road test to confirm existence of a problem.

Preliminary inspection consists of visual checks designed to
rule out faults caused by leaks, fuel line damage, or loose elec-
trical connections.

 

Preliminary Inspection

 

1.

Check fuel gauge readings for main and auxiliary tanks.

2.

Visually inspect fuel lines at tanks, selector valve, fuel
pump, and at engine. Look for loose, damaged, leaking
lines.

3.

Check vacuum actuator hose on turbo diesel models.

4.

Check wiring for fuel lift pump.

5.

Check glow plug and relay wiring. Also check electronic
accelerator pedal wiring on turbo diesel. Look for loose
connections at all points (including battery), or for
damaged, pinched wires.

6.

Check serpentine drive belt tension and condition. 

7.

Note if any indicator lights are on. If engine runs, also
check voltage, oil pressure, and coolant temperature
readings.

8.

Check exhaust system components for damage, loose joint
connections, or grounding against body.

9.

Inspect transmission linkage and wiring connections,
especially if vehicle is used for off road operation.

10. If vehicle is drivable, and no obvious problems are found,

road test vehicle. If vehicle is not drivable, refer to
diagnosis charts and scan tool diagnosis.

 

Road Test

 

1.

Note battery voltage. Low voltage can cause PCM power-
up and initialization problems. Battery voltage should be 
no lower than 11.5 volts for satisfactory operation.

2.

Connect scan tool to diagnostic link connector. Set tool to
record fault codes, or have helper use tool to interrogate
system during test.

3.

Start engine and check idle operation. Note any faults such
as rough idle, stalling, excessive smoke.

4.

Apply service brake and shift transmission into drive
range. Note if engine stalls, runs rough, or another fault
occurs.

5.

Drive vehicle on road at posted limits. Note operation
under light and heavy acceleration, and at normal cruise
speeds. Note faults such as surge, miss, vibration, noise,
low power, smoke (blue, black, white).

6.

Shift into neutral at cruise speed and note engine
operation. If vibration or noise was experienced but it now
stops, problem may be with drive belt, engine mount,
accessory, U-joint, or torque converter.

7.

Return to shop and note fault codes recorded by PCM . If a
fuel system fault was noted during road test, refer to
diagnosis charts, perform fuel system tests, and check
system electrical components with scan tool.

 

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 Fuel, Emissions, and Exhaust  3-7

  

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5745159

 

 Fuel System Diagnosis—Diesel Engine

 

PROBLEM

POTENTIAL CAUSE

CORRECTION

 

Hard Starting

1.

Driver/owner not following recommended 
start procedure.

1.

Remind driver/owner of required procedure. Dem-
onstrate procedure if necessary.

2.

Fuel contaminated, low quality, or wrong 
fuel.

2.

Drain off sample at fuel filter drain plug. Flush
tank, lines, and filter if fuel is contaminated, wrong
grade or type, suspect quality, or shows wax
buildup.

3.

Air filter plugged.

3.

Remove and clean filter, housing, air horn and inlet
hose. Replace filter if plugged.

4.

Excessive water in fuel filter.

4.

Drain off water at drain plug. Then remove, clean,
and reinstall filter.

5.

Fuel pump intermittent or not energized by 
relay.

5.

Check fuel pump circuit fuse, relay, wiring.

6.

Fuel-lift pump fault.

6.

Test pump pressure at pump outlet. Replace pump
if pressure is below 5.8 psi (40 kPa).

7.

Fuel return, drain, or vent line restricted, 
plugged, or damaged.

7.

Check lines for damage. Verify flow with com-
pressed air. Repair or replace lines as necessary.

8.

Coolant temperature sensor fault.

8.

Repair wiring or replace sensor if temperature
readings are 5° greater or less than actual ambient
air temperature. High resistance in sensor or cir-
cuit wiring will cause this.

9.

Glow plug fault.

9.

Test voltage to and from relay/controller, and at
plugs. Repair wiring, replace relay/controller, or
replace glow plug(s) as needed. Refer to test pro-
cedures in this section and in sections 2 and 12.

10. Shut-off solenoid fault.

10. Test and replace solenoid if necessary. Be sure

solenoid fuse and wiring are OK beforehand. Look
for bad connections if problem is intermittent.

11. No cranking signal to PCM 

11. Test with scan tool. Look for bad ground, connec-

tions, or damaged/failed crankshaft position
sensor.

12. Exhaust 

system 

restriction.

12. Look for damaged pipes, muffler, converter,

especially on vehicles used off road.

13. Low engine cranking speed.

13. Check state of charge of batteries, load test and

check connections. Refer to test procedures in
Section 12. Check engine oil viscosity to ensure it
is correct for the ambient temperature. Refer to
specifications in Section 1. Check starter draw to
determine if starter is dragging. Refer to test
procedure in Section 12.

 

3-8

Fuel, Emissions, and Exhaust

 

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No Start Condi-
tion (engine 
cranks but will 
not run)

1.

Excessive amount of water or wax buildup in 
system.

1.

Draw off sample at drain plug. Drain and flush sys-
tem if necessary.

2.

Blown fuse.

2.

Replace fuse. Check for shorts-grounds in affected
circuit.

3.

No fuel to injection pump.

3.

Test fuel-lift pump output. Replace pump if pres-
sure is below 5.8 psi (40 kPa). Check lines and
filter for restrictions if pump output is OK. Also
test pump relay. Be sure pump relay is being
energized when ignition switch is in crank or start
position. Check fuel level in tanks

4.

No fuel to injectors.

4.

Check shut off solenoid. Check fuel solenoid
driver feed (terminal A) and ground (terminal C)
circuits.

5.

Engine fault:

• broken camshaft

• damaged injection pump gears

• timing chain or gear failure

5.

Inspect and repair as needed.

6.

Fuel tank select valve problem.

6.

Replace valve if it won’t switch from main to aux-
iliary and back. NOTE: the valve will only operate
if the fuel lift pump is energized!

7.

No inject signal from PCM.

7.

Run scan tool test and replace failed sensor,
harness wire, or connector.

8.

Injection pump failure.

8.

Replace pump but only if failure is indicated by
scan tool and pressure test.

9.

PCM ground or feed circuit fault (on ground 
or ignition voltage reference signal).

9.

Confirm with scan tool. Use multimeter to locate
fault.

10. PCM fault.

10. Confirm with scan tool before replacement.

Engine Starts 
then Stalls

1.

Air leak in fuel feed line.

1.

Inspect lines and repair as needed. Bleed injectors 
afterward.

2.

Glow plug fault (cold ambient temperature).

2.

Test and repair wiring, or replace failed glow plugs
or relay/controller.

3.

Restriction in fuel tank vent or return lines.

3.

Inspect  and  clear  restriction.  Replace  cap  vent,  or
lines as needed.

4.

Fuel-lift pump pressure below 2 psi (14 kPa) 
at injection pump, or 5.8 psi (40 kPa) at fuel 
pump outlet.

4.

Replace pump but only if fuel lines to pump are not
blocked, plugged, or restricted. Also be sure flow
through 2-stage filter is not restricted as well.

5.

Idle rpm too low.

5.

Adjust idle to required rpm.

6.

No injection signal to PCM (turbo diesel).

6.

Test with scan tool and replace failed sensor or
harness.

 

 Fuel System Diagnosis—Diesel Engine

 

PROBLEM

POTENTIAL CAUSE

CORRECTION