Pontiac FIREBIRD 1972 Service Manual page 737

ENGINE TUNE-UP
TUNE-UP SEQUENCE INDEX
Spark Plug Removal
...............................................
6C-1
Compression Test
...................................................
6C-1
Spark Plugs-Clean-Test-Install
................................
6C-2
Ignition System-Service and Repairs
......................
6C-3
Battery and Battery Cables-Clean and Test
..........
6C-4
Generator
................................................................
6C-4
Fan Belt-Inspect and Adjust
..................................
6C-4
Manifold Heat Valve-Check Operation
..................
6C-4
Intake Manifold Bolts-Check
..................................
6C-4
Air Cleaner-Service
..................................................
6C-5
Fuel Lines and Filter-Inspect and Service
............
6C-5
GENERAL INFORMATION
Engine tune-up can be described as diagnosis and preven-
tative maintenance performed at regular intervals to re-
store maximum performance and economy in an engine.
It is advisable to follow a definite and thorough procedure
of analysis and correction as suggested by the sequence-
index above.
IMPORTANT: A quality tune-up is recom-
mended every 12 months or 1 2 , m miles in
order to assure proper engine performance and
complete effectiveness o f exhaust emission sys-
tems.
SPARK PLUG REMOVAL
Remove any foreign matter from around spark plugs by
blowing out with compressed air, then disconnect wires
and remove plugs.
COMPRESSION TEST
Test compression with engine warm, all spark plugs
removed and throttle and choke wide open. Crank engine
through at least five compression strokes to obtain highest
possible reading. No cylinder should be less than 80% of
the highest cylinder (see examples). Excessive variation
between cylinders, accompanied by low speed missing of
the cylinder or cylinders which are low, usually indicates
Cooling System-Inspect and Service
......................
6C-5
Lubrication System-Inspect
....................................
6C-5
Choke Adjustment
..................................................
6C-5
Idle Stop Solenoid
....................................................
6C-5
Tune-up Equipment-Connect
................................
6C-5
Test Dwell
............................................................
6C-5
Test Ignition Timing and Spark Advance
..........
6C-6
Check Idle Speed and Mixture
..........................
6C-6
Positive Crankcase Ventilation
................................
6C-6
Road Test
................................................................
6C-6
piston ring. Low pressures, even though uniform, may
indicate worn rings. This will usually be accompanied by
excessive oil consumption.
6 CYL.
Example 1
CYLINDER PRESSURE
80% of 140 (highest) is 112. Thus cylinder No. 6 is less
than 80% of No. 3. This condition, accompanied by low
speed missing, indicates a burned valve or broken piston
ring.
Example
2
CYLINDER PRESSURE
1
......................................................................
95
2
....................................................................
106
3
..................................................................
100
4
......................................................................
97
5
......................................................................
95
6
....................................................................
101
80% of 106 is 85. While all cylinders are well above 85,
they are all excessively low. This may indicate poor valves
in all cylinders or low cranking speed.
If compression is subnormal, tune-up will probably not be
a valve not properly seating, a burned valve or broken
satisfactory.