Pontiac Fiero 1988 Service Manual page 553

6 E 2 - C 4 - 6 DRIVEABILITY A N D EMISSIONS - F U E L INJECTION (TBI)
POWER / G R O U N D
CONNECTOR
6-WAY IGN.
MODULE
CONNECTOR
I
M O D U L E / C O I L
ASSEMBLY
COIL
ASSEMBLIES
ECM FUSE
- # » " X # ~ —
-IGN
PNK/BLK 439
W16
BLK/RED 453
PPL/WHT 430
TAN/BLK 424
WHT 423
B16
B9
W19
W6
SECONDARY
11-21-86
PRIMARY
WINDING
WHT 121
—I
DIRECT IGNITION
S Y S T E M MODULE
TO I.P. OR
v -
TACH S
E C M
IGN
GROUND
REFERENCE
BY-PASS
EST
* 7 S 3332-6E
11-10-86
CHART
C-4D-1
"DIS" MISFIRE AT IDLE
2.5L "P" SERIES (TBI)
Circuit Description:
The Direct Ignition System (DIS) uses a waste spark method of distribution. In this type of system, the
ignition module triggers the #1/4 coil pair resulting in both #1 and #4 spark plugs firing at the same time. #1
cylinder is on the compression stroke at the same time #4 is on the exhaust stroke, resulting in a lower energy
requirement to fire #4 spark plug. This leaves the remainder of the high voltage to be used to fire #1 spark plug.
On this application, the crank sensor is mounted to the bottom of the coil/module assembly and protrudes through
the block to within approximately .050" of the crankshaft reluctor. Since the reluctor is a machined portion of the
crankshaft and the crank sensor is mounted in a fixed position on the block, timing adjustments are not possible
or necessary.
Test Description:
Numbers below refer to circled
numbers on the diagnostic chart.
1. If the "Misfire" complaint exists under load only,
the diagnostic chart on page 2 must be used.
Engine rpm should drop approximately equally on
all plug leads.
2. A spark tester such as a ST-125 must be used
because it is essential to verify adequate available
secondary voltage at the spark plug. (25,000
volts).
3. If the spark jumps the test gap after grounding the
opposite plug wire, it indicates excessive
resistance in the plug which was bypassed. A
faulty or poor connection at that plug could also
result in the miss condition. Also check for carbon
deposits inside the spark plug boot.
4. If carbon tracking is evident, replace coil and be
sure plug wires relating to that coil are clean and
tight. Excessive wire resistance or faulty
connections could have caused the coil to be
damaged.
5. If the no spark condition follows the suspected coil,
that coil is faulty. Otherwise, the ignition module
is the cause of no spark. This test could also be
performed by substituting a known good coil for
the one causing the no spark condition.