Hummer H1 Service Manual page 49

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2-12 Engine
PROBLEM
White Smoke 1. Low quality fuel.
2. Injection pump/engine timing is retarded.
3. Engine coolant entering combustion chamber
through blown gasket, cracked head, loose/
damaged head bolts. May be accompanied
by low coolant level and overheating.
4. Low ambient temperatures (below freezing).
Black Smoke 1. Low grade diesel fuel.
2. Overrich fuel mixture:
¥ Drain/return lines restricted.
¥ Injector(s) stuck open.
¥ Engine speed or throttle sensor fault.
3 Black smoke at wide open throttle.
Gray Smoke 1. Long idle periods.
2. Low grade fuel.
3. Fuel tank vent restricted.
4. Fuel return line restricted.
5. Engine problem (low compression excessive
blowby, worn rings or valve stem seals).
Engine Diagnosis
POTENTIAL CAUSE CORRECTION
1. Drain and reÞll tank with better quality fuel.
2. Check and correct timing.
3. Verify problem and repair as necessary. Replace
cracked head, block, or head gasket.
4. Normal condition caused primarily by water vapor.
Not a concern unless it continues after warmup.
1. Drain and reÞll tank.
2. Test, diagnose and repair as required.
3. Restriction in air intake system, no vacuum to
wastegate actuator, damaged wastegate, or air leak
at intake or exhaust manifold.
1. Try to avoid prolonged idling.
2. Add proper quality fuel. (not necessary to drain and
reÞll tank).
3. Clear vent and line.
4. Clear restriction. Replace line if kinked or pinched.
5. Diagnose and repair as indicated.
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