GMC 1976 ZEO 6083 Maintenance Manual page 275

6A- 10
ENGINE
ENGINE RUNS
GENERAL
Overheating (Refer to "Engine Overheats"
in this section) .
Detonation or pre-ignition .
Sub-standard fuel .
Faulty or dirty air cleaner.
Valve train faulty or worn .
Mild vapor lock .
Exhaust vapor lock .
Exhaust manifold clogged or restricted .
Air cleaner plugged.
FUEL
Faulty fuel pump .
Restricted fuel filter.
Choke valve not completely closed .
Carburetor throttle lever loose on shaft.
Exhaust manifold clogged with carbon .
Exhaust manifold, muffler, or tail pipe
restricted .
Intermittent delivery of fuel to carbu-
retor so that momentarily the mixture is too
weak for combustion .
ENGINE RUNS - MISSES ERRATICALLY AT ALL SPEEDS (1)
GENERAL
Restricted exhaust .
Compression low.
Internal coolant leakage .
Engine overheating. (11)
Timing improperly set.
MECHANICAL
Compression leak at head gasket
cylinders (This can be noted when
occurs in two adjacent cylinders) .
Intermittently sticking valves .
Broken valve spring .
Valve(s) held open slightly by faulty
mechanism.
IGNITION (2)
- MISSES AT HIGH SPEED ONLY (1)
IGNITION (2)
or between
missing
Wrong type spark plugs.
Fouled spark plug or broken porcelain.
Faulty spark plug cables .
Clean, gap, and/or replace spark plugs, as
necessary.
Too hot spark plugs-change to colder type,
but note that a hot plug may be due to loose
installation or lack of plug gasket (if gasket
is called for) .
Ignition point gap much too wide or pitted .
Breaker arm binding or sticking .
Breaker arm weak .
Weak spark, coil, or condenser.
Improper ignition timing and/or dwell .
Centrifical advance not functioning
properly .
Distributor cam lobe or shaft worn .
Worn rotor or damaged distributor cap.
MECHANICAL
Incorrect valve timing .
Sticking hydraulic lifters.
Valve springs broken .
Valve springs shimmy .
Valve springs too weak to close valves
promptly .
Low battery voltage.
Low generator voltage.
Burned or pitted ignition points .
Incorrect ignition point gap.
Faulty condenser or coil .
Weak spark or no spark in one or more
cylinders.
Faulty distributor cap or rotor.
Primary circuit restricted or open inter-
mittently.
Primary circuit detoured by short inter-
mittently.
Secondary circuit restricted or open in-
termittently .
Secondary circuit detoured by short inter-
mittently .
FUEL
Fuel pump faulty .
Needle valve in carburetor sticking .
Improper float lever. (4)
Mixture too rich or too lean .
Passage in carburetor dirty.