MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
SERVICE MANUAL NUMBER 23
Page 5B-30
90-861326--1 MARCH 1999
Base Ignition Timing
In order to check or change base timing on a HEI system the ECM has to be entered into
the service mode by using a scan tool or code tool. The IC module will go to base timing.
The ECM will stabilize timing to allow timing adjustment. The ECM incorporates a spark con-
trol override, which allows timing to be lowered if spark knock (detonation) is encountered
during normal operation. At this time, the timing can be adjusted by turning the distributor.
p
o
n
m
l
k
j
i
h
g
f
e
d
c
b
a
t
s
Distributor Module Mode
j
k
n
m
l
r
q
i
h
g
f
e
d
c
b
a
ECM Control Module
Downloaded from
https://needmanual.com/
Index
