Chevrolet Light Duty Truck 1973 Service Manual page 347

screw to obtain 1600 rpm with screw on top step of fast
idle cam.
On Light-Duty vehicles with manual transmission, adjust
fast idle screw to obtain 1300 rpm with screw on top step
of fast idle cam and distributor spark advance hose
disconnected.
Reconnect "Fuel Tank" line to vapor canister and
reconnect distributor spark advance hose.
• 454 Cu. In. (Four-Barrel Carburetor)
On Light-Duty vehicles, disconnect "Fuel Tank" line
from Evaporation Emission vapor canister.
Disconnect the distributor spark advance hose and plug
the vacuum source opening.
Adjust Idle Stop Solenoid (turn solenoid body, using hex
nut) to obtain:
A D D ITIO N A L CHECKS A N D ADJUSTMENTS
CYLINDER BALANCE TEST
(FIG. 1 8 )
It is often difficult to locate a weak cylinder. A
compression test, for example, will not locate a leaky
intake manifold, a valve not opening properly due to a
worn camshaft, or a defective spark plug.
With the cylinder balance test, the power output of one
cylinder may be checked against another, using a set of
grounding leads. When the power output of each
cylinder is pot equal, the engine will lose power and run
roughly.
Perform a cylinder balance test as follows:
1. Connect the tachometer and vacuum gauge.
2. Start engine and run at 1500 rpm.
3. Ground large clip of grounding leads and connect
individual leads to all spark plugs except the pair
being tested.
Divide the firing order in half and arrange one half
over the other. The cylinders to be tested together
appear one over the other.
L Firing Order
6
1-5-3-6-2-4 = 1-5-3 = 1-6, 5-2, 3-4
V Fifing Order
8
1-8-4-3-6-5-7-2 = 1-84-3 = 1-6, 8-5, 4-7,3-2
4. Operate engine on each pair of cylinders in turn
and note engine rpm and manifold vacuum for
each pair. A variation of more than 1 inch of
vacuum or 40 rpm between pairs of cylinders being
tested indicates that the cylinders are off balance.
6-5-7-2
700 rpm on all Heavy Duty vehicles - automatic
transmission in "Park" ; manuaPMransmission in
neutral.
6V 00 rpm on Light-Duty vehicles with automatic
C
transmission (in Drive).
900 rpm on Light-Duty vehicles with manual
transmission (in neutral).
On Light Duty vehicles with automatic transmission,
_ig£onnect distributor spark advance hose. Adjust fast idle
screw to obtain 1600 rpm with screw on top step of fast
idle cam. ^
On Light-Duty vehicles with manual transmission, adjust
fast idle screw to obtain 1600 rpm with screw on top step
of fast idle cam and distributor spark advaii%" hos£
disconnected.
Reconnect "Fuel Tank" line to vapor^anister and
reconnect distributor spark advance hose.
BATTERY
The battery should be checked with special testing
equipment and to the equipment manufacturers
specifications. See Section
on battery tests.
IG N ITIO N
The following additional ignition checks may be made
with any of several pieces of equipment available for
uncovering the source of engine difficulties. The specific
operating instructions of the equipment manufacturer
should be followed.
• Cranking voltage
• Ignition switch
• Distributor resistance
EN G IN E * 6-11
: v*8 "'
Y for complete information
6
LIGHT DUTY TRUCK SERVICE MAfUAL
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