Hummer H1 Service Manual page 144

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PROBLEM
Hard Starting 1. Driver/owner not following recommended
start procedure.
2. Fuel contaminated, low quality, or wrong
fuel.
3. Air filter plugged.
4. Excessive water in fuel filter.
5. Fuel pump intermittent or not energized by
relay.
6. Fuel-lift pump fault.
7. Fuel return, drain, or vent line restricted,
plugged, or damaged.
8. Coolant temperature sensor fault.
9. Glow plug fault.
10. Shut-off solenoid fault.
11. No cranking signal to PCM
12. Exhaust system restriction.
13. Low engine cranking speed.
5745159
Fuel System Diagnosis—Diesel Engine
POTENTIAL CAUSE
Fuel, Emissions, and Exhaust
CORRECTION
1. Remind driver/owner of required procedure. Dem-
onstrate procedure if necessary.
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. Remove and clean filter, housing, air horn and inlet
hose. Replace filter if plugged.
4. Drain off water at drain plug. Then remove, clean,
and reinstall filter.
5. Check fuel pump circuit fuse, relay, wiring.
6. Test pump pressure at pump outlet. Replace pump
if pressure is below 5.8 psi (40 kPa).
7. Check lines for damage. Verify flow with com-
pressed air. Repair or replace lines as necessary.
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. 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. Test and replace solenoid if necessary. Be sure
solenoid fuse and wiring are OK beforehand. Look
for bad connections if problem is intermittent.
11. Test with scan tool. Look for bad ground, connec-
tions, or damaged/failed crankshaft position
sensor.
12. Look for damaged pipes, muffler, converter,
especially on vehicles used off road.
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.
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