GMC 1976 ZEO 6083 Maintenance Manual page 276

ENGINE RUNS - MISSES STEADILY AT ALL SPEEDS (1)
GENERAL
Worn camshaft lobes.
Compression low.
Vacuum leak in intake manifold . (9)
Dwell and timing off.
Fuel poor quality.
FUEL
Dirty jets in carburetor .
Water or dirt in fuel .
Fuel filter plugged.
Fuel pump worn or diaphragm faulty .
ENGINE RUNS - BUT MISSES ON ONE CYLINDER
MECHANICAL GENERAL
Compression leaking.
Vacuum leak at intake manifold . (9)
Timing and/or dwell improperly set.
Overheated engine . (Refer to "ENGINE
OVERHEATS" in this section) .
Clogged exhaust .
IGNITION (2)
Defective spark plug or spark
Distributor cap defective.
Distributor cam worn .
Points worn or improperly aligned.
FUEL
Fuel pump faulty .
Carburetor faulty .
plug wire .
ENGINE RUNS - BUT MISSES ON DIFFERENT CYLINDERS
IGNITION (2)
Dirty or incorrectly set points .
Worn, dirty, or gap set too wide in spark
plugs.
Worn distributor shaft.
Cam worn or burned distributor rotor.
Faulty coil or condenser.
Insufficient spring tension on points .
MECHANICAL
Valve train faulty .
Valve train defective.
Stuck hydraulic lifter .
Defective rings or piston .
Faulty rings .
Faulty valve train.
ENGINE
6A- 1 1
GENERAL
IGNITION (2)
Compression leaking.
Spark plugs faulty .
Vacuum leak at intake manifold or
Coil wire or distributor cap faulty .
carburetor . (9)
Distributor cam worn .
Defective head gasket .
Points worn or improperly set.
Dwell, timing off. Distributor rotor faulty .
Poor grade fuel .
Carbon in engine.
MECHANICAL
Restricted exhaust.