Chevrolet 10 Series 1968, Service Manual, Page: 355 / 713

ENGINE 6-8
F ig . 14—Crankcase V e n tilation V a lv e
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 not equal, the engine w ill 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 ap­
pear one over the other.
L6 Firing Order
1-5-3-6-2-4 = 1-5-3 = 1-6, 5-2, 3-4
6-2-4
V8 Firing Order
1-8-4-3-6-5-7-2 = 1-8-4-3 = 1-6, 8-5, 4-7, 3-2
6-5-7-2
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.
Battery
The battery should be checked with special testing
equipment and to the equipment manufacturers specifi­
cations.
See Section 6Y for complete information on
battery tests.
Ignition
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
• Secondary resistance
• Ignition output and secondary leakage
C ra n k in g V oltage (Fig. 16)
1. Disconnect coil primary lead at the coil negative
terminal to prevent engine from firing during
cranking.
2. Connect voltmeter between primary terminal of coil
(resistance wire side) and ground.
3. Operate starting motor.
a. If voltage is 9 volts or more and cranking speed
is satisfactory, the battery, starter, cables,
starter switch and ignition circuit to coil (by­
passing resistance wire) are in good condition.
b. If below 9 volts, check circuit until difficulty is
located.
Meter reading below specification—Weak bat­
tery; defective cables, connections, switch or
starter; defective ignition circuit to coil.
Cranking speed below normal- Excessive re-
F ig . 16—Testing Cranking Voltage
CHEVROLET TRUCK SERVICE MANUAL