Pontiac Fiero 1988 Service Manual page 549

6E2-C4-2 DRIVEABILITY A M D EMISSIONS - FUEL INJECTION (TBI)
m C R A N K S H A F T R E L U C T O R
m
C R A N K S H A F T S E N S O R
m
D I S A S S E M B L Y
7S
3252-6E
Figure C4-1 Sensor To Crank Reluctor Relationship
The second crank pulse following the "sync pulse"
signals the "DIS" module to fire the #2/3 ignition coil
and the fifth crank pulse signals the module to fire the
# 1/4 ignition coil.
I g n i t i o n Coils
Two separate coils are mounted to the Module
assembly (Figure
C4-2).
Each coil provides the spark
for two plugs simultaneously (Waste Spark
Distribution). Each coil can also be replaced
separately.
DIS Module
The "DIS" Module monitors the Crank Sensor
signals and based on these signals sends a reference
signal to the ECM so that correct spark and fuel
injector control can be maintained during all driving
conditions. During cranking, the "DIS" module
monitors the "sync-pulse" to begin the ignition firing
sequence and below 400 rpm the module controls
spark advance by triggering each of the two coils at a
pre-determined interval based on engine speed only.
Above 400 rpm the ECM controls the spark timing
(EST) and compensates for all driving conditions. The
"DIS" module must receive a "sync-pulse" and then a
Crank Signal in that order to enable the engine to
start.
p n #2/3 IGN. COIL [T] C R A N K S H A F T S E N S O R
|T1 #1/4 IGN. COIL [jF]
BOLT (3) 27 N-m (20 L B S . FT.)
fin
IGN. M O D U L E 7S-3194-6E
Figure
C4-2
Ignition
Coils,Module
and Sensor (2.5L)
The "DIS" module is not repairable. When a
module is replaced, the remaining "DIS" components
must be transferred to the new module. (See Figure
C4-2)
Electronic Spark Timing (EST)
This system uses the same EST to ECM circuits
that distributor type systems use. Following is a brief
description for each of the EST circuits.
• "DIS" Reference - CKT 430.
The crankshaft sensor generates a signal to the
ignition module which results a reference pulse
being sent to the ECM. The ECM uses this signal
to calculate crankshaft position and engine speed
and injector pulse width.
• Reference ground - CKT 453.
This wire is grounded through the module and
insures that the ground circuit has no voltage drop
between the ignition module and the ECM, which
could affect performance.
• By-Pass - CKT 424.
At about 400 rpm, the ECM applies 5 volts to this
circuit to switch spark timing control from the
"DIS" module to the ECM. An open or grounded
by-pass circuit will set a Code 42 and result in the
engine operating in a back-up ignition timing
mode (module timing) at a calculated timing
value. This may cause poor performance and
reduced fuel economy,
o EST-CKT 423.
The "DIS" module sends a reference signal to the
ECM when the engine is cranking. While the
engine is under 400 rpm, the "DIS" module
controls the ignition timing. When the engine
speed exceeds 400 rpm, the ECM applies 5 volts to
the "By-pass" line to switch the timing to ECM
control (EST).