GMC 4000 Series Service Manual page 315

Sec. 6B
Page 304
TORO-FLOW DIESEL ENGINE
SYMPTOM D - WRONG TYPE OF FUEL
POSSIBLE CAUSE
1. Improper grade or type of fuel in tank.
SYMPTOM A - UNEVEN RUNNING OR FREQUENT STALLING
POSSIBLE CAUSES
1. Idle speed set too slow.
2. Cylinder m isfiring.
3. Burned or sticking valves.
4. Engine temperature too hot or too cold.
5. Fuel system deficiencies.
SYMPTOM B - DETONATION
POSSIBLE CAUSES
1. Improper injection timing.
2. Defective injection nozzles.
SYMPTOM C - LACK OF POWER
POSSIBLE CAUSES
1. Improper valve lash.
2. Insufficient fuel.
3. Insufficient air.
4. E xcessive exhaust back-pressure.
5. Improper engine operating temperature.
6. Low cylinder com pression.
(NOTE: Make checks with engine at normal operating temperature.)
SYMPTOM A - EXCESSIVE BLACK OR GRAY SMOKE
POSSIBLE CAUSES
1. Insufficient combustion air.
2. Exhaust pipe or muffler clogged or pinched.
G M C S E R V I C E M A N U A L
HARD STARTING (CONT'D)
1.
A BN O R M A L ENGINE OPERATION
1.
2. Check for m isfiring cylinder, replace or over­
3. Inspect valve operating mechanism and check
4. Check thermostats, fan belt tension, and coolant
5. Refer to item s 4 through 10 under "Hard Start­
2. Remove nozzles and check on test stand.
2. Check for drop in fuel pressure, using gauges
3. Check for damaged or clogged air cleaners and
4. Inspect exhaust system components, replace
6. See Symptom B under "Hard Starting"diagnosis.
EXHAUST ANALYSIS
1.
2. Repair or replace parts as necessary.
REMEDY
Fill tank with proper fuel referring to current
GMC D iesel Fuel Oil Bulletin.
REMEDY
Adjust idle speed to 625 to 650 rpm.
haul fuel injection nozzle assem bly.
cylinder com pression. Overhaul cylinder head if
necessary.
level. Correct as necessary.
ing" Symptom C.
REMEDY
1.
Check and, if necessary, set injection timing
properly.
REMEDY
1.
Set to specified valve clearance.
at secondary fuel filter.
intake passages. Service air cleaners or repair
as required.
damaged or clogged units.
5. Inspect and correct cooling system .
REMEDY
Service air cleaners and check for other r e ­
strictions.