1988 PONTIAC FIERO Service Repair Manual

6E3-A-92 2.8b (VIN SI DRIVEABILITY AND EMISSIONS
TO OIL PRESS. SW.
&FUEL PUMP RELAY
FUSE
& HOLDER BATTERY 12
V
.. am.. . FUSIBLE LINK 15 WAY
439
PNWBLK
- 419 BUNNVHT
SERIAL DATA
451
WHTIBLK
450 BLWHT
ALDL CONNECTOR
CHART A-2
NO ALDL OR WONT FLASH CODE 12
""SERVICE ENGlNE SOON" MGHT ""8N13SPEADY
2.8L (VIN S) ""FYSERlES (PORT)
Circuit Description:
There should always be a steady "Service Engine Soon" light when the ignition is "ON" and engine stopped.
Battery ignition voltage is supplied to the light bulb. The electronic control module
(ECM) will turn the light
"ON" by grounding CKT
419 at the ECM.
With the diagnostic terminal grounded, the light should flash
a Code 12, followed by any trouble code(s)
stored in memory.
A steady light suggests a short to ground in the light control CKT 419, or an open in diagnostic CKT 451.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. If there is a problem with the ECM that causes a
"Scan" tool to not read serial data, the ECM
should not flash a Code 12. If Code 12 is flashing
check for CKT
451 short to ground. If Code 12
does flash be sure that the "Scan" tool is working
properly on another vehicle. If the "Scan" is
functioning properly and CKT 461 is OK the
PROM or ECM may be at fault for the NO
AL,DI,
symptom.
2. If
the light goes "OFF" when the ECM connector is
disconnected, CKT 419 is not shorted to ground.
3. This step will check for an open diagnostic CKrl'
451.
4. At this point the "Service Engine Soon" light
wiring is OK. The problem is a faulty ECM or
PROM. If Code 12 does not flash, the ECM should
he replaced using the original PROM. Replace the
PROM only after trying an ECM, as a defective
PROM is an unlikely cause of the problem.
Diagnostic Aids:
Solenoids and relays are turned "ON" or "OFF" by
the ECM using internal electronic switches called
"drivers". Each driver is part of a group of four called
"Quad-l)rivers". Failure of one driver can damage
any other driver in the set.
Hefore replacing ECM, be sure to check the coil
resistance of
all solenoids and relays controlled by the
14:CM. Set: I':C%f wiring cliugrntn for the solcnoid(s)
.c~~cl rel;~ (-1 ~ititl lllc coil tcrtriitlul itlentilication.

DRIVEABILITY AND EMISSIONS 2.8b (VIN 5) 6E3-A-13
CHART A-2
NO ALDL DATA OR WONRT FLASH CODE 12
DISCONNECT ECM CONNECTORS.
IGNITION "ON" AND NOTE SHORT TO
GND. BETWEEN ECM AND ALDL
IGNITION "ON", ENGINE STOPPED.
KT
451, WITH TEST
IF OK, REPLACE ECM USING ORIGINAL PROM. TERMS.
"B" AND CKT 451 TO ECM.

6E3-A-14 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
PICK-UP COIL
CHART A-3
(Page 1 of 2)
ENGINE CRANKS BUT WON'T RUN
2.8L (VIN S) ""F'" SERIES (PORT)
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. This chart
assunles that battery condition and
engine cranking speed are OK, and there is
adequate fuel in the tank. If engine starts but
immediately stalls, see "Symptoms", Section
"B"
(Hard Start). A "Service Engine Soon" light "ON"
is a basic check for ignition and battery supply to
the electronic control module
(ECM).
2. No sparlc indicates a basic HE1 problem.
3. This test will determine if the ECM is receiving
the reference signal and controlling the injectors.
This test could also be performed at the 4-way
injector connector by using a test light between
terminals
"A" and "D".
If the test light "blinks" while cranking, then
ECM control should be considered OK.
How
bright the test light "blinks" is not important.
However, the test light should be a
5-34730-2 or
equivalent.
4. Use pressure gage 5-34730-1. Wrap a shop towel
around the fuel pressure tap to absorb any small
amount of fuel leakage that may occur when
installing the gage.
Diagnostic Aids:
@ An EGR valve sticking open can cause a low
airlfuel ratio during cranking. Unless engine
enters "Clear Flood" at the first indication of a
flooding condition, it can result in a no start.
@ Check for fouled plugs:
@ If the TPS is sticking or binding in the wide open
throttle position, the ECM will be in the "Clear
Flood" mode.
@ A defective cold start circuit or water in fuel line
can cause a no start in cold weather.
To check cold
start circuit: See CHART
A-9.
e A defective MAF sensor may cause a no start or a
stall after start. 'I'o determine if the sensor is
causing the problem, disconnect it. The ECM will
then use a default value for the sensor, and if the
condition is corrected and the connections are OK,
replace the sensor.
@ Also check that injectors on both sides of engine
will cause a test light to "blink". Checking of two
injectors on each bank in this manner will locate a
shorted injector.
If
above are all OK, refer to "Symptoms" in
Section
"R" "Hard Start".
@ Also checlc that injectors are not open or shorted.
Injector resistance should be greater than ohms.

NOTICE: FUEL SYSTEM UNDER PRESSURE. TO AVOID FUEL
SPILLAGE, REFER TO FIELD SERVICE PROCEDURES FOR
TESTING OR MAKING REPAIRS
REQUlRlNG DISASSEMBLY OF
FUEL
LINES OR FITTINGS.
IGN. "ON" -IF "SES" LIGHT IS "OFF", SEE CHART A-I. r INSTALL "SCAN" TOOL - IF "NO ALDL", SEE CHART A-2. r CHECK THE FOLLOWING: r TPS - IF OVER 2.5V AT CLOSED THROTTLE, SEE CODE 21.
NOTICE
: 80 MOT
OR EQUIVALENT TO INJECTOR, TERMINALS R TERMINALS. TO SHORT OR TOUCH ILE CRANKING. TOGETHER WHILE
CRANKING OR ECM
MAY BE
DAMAGED.
SHOULD BE GREATER THAN 8
DIAGNOSTIC
&-,-m.---&?-a
TROUBLE FOUND. REVIEW
" CLEAR CODES AND CONFIRM "CLOSED LOOP " OPERATION AND NO "SERVICE ENGINE SOON " LIGHT.

CHART A-3
(Page 2 of 2)
ENGINE CRANKS BUT WONT WN
2.8L (VIN S) ""FYSERIES (PORT)
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
5. Checks for 12 volt supply to injectors.
6. This
test will determine if the distributor module
is not generating the reference pulse or if the
wiring or ECM are at fault. By touching CKT 430
with a test light a reference signal is being
generated. If the test light
(5-34730-2) blinks at
the injector, then the ECM and wiring is OK.
7. Each time
the test light touches CKT 430, the
ECM should turn "ON" the fuel
punlp for 2
seconds.
8. All
checks made to this point would indicate that
the ECM is at fault. However, there is
a
possibility of CKT 467 or 468 being shorted to a
voltage source either in the engine harness or in
the injector harness. To
test for this condition:
@ Disconnect the injector 4-way connector.
@ Ignition "ON"
Probe
CKTs 467 and 468 on the ECM side of
harness with a test light connected to ground.
There should be no light.
@ If OK, check the resistance of the injector
harness between terminals
"A & C", "A & D",
"B & D", and .'B & C".
@ Should be more than 4 ohms
@ If less than 4 ohms check harness for wires
shorted together and check each injector
resistance.
@ Resistance should be more than 10 ohms.
@ If all OK, replace ECM.

DRIVEABILITY AND EMISSIONS 2.8L (VIM 5) 6E3-A-17
REFER TO FIELD SERVICE PROCEDURES FOR TESTING OR MAKING
REPAIRS REQUIRING DISASSEMBLY
OFFUEL LINES OR FInlNGS
P=---=-'-"""
I CHARTA-3 I
PAGE 1 OF2
ARALLEL THERE SHOULD BE A IGHT ON BOTH TERMINALS.
r DISCONNECT DISTRIBUTOR 4-WAY
CONNECTOR.
r MOMENTARILY TOUCH HARNESS
CONNECTOR TERMINAL CKT 430 WITH TEST LIGHT TO 12 VOLTS.
* CLEAR CODES AND CONFIRM "CLOSED LOOP " OPERATION AND NO "SERVICE ENGINE SOON " LIGHT.

6E3-A-I8 2.8b (VIN 5) DRIVEABILITY AND EMISSIONS
PUMP INLET FILTER
IN-TANK PUMP
FUEL
PRESSURE CONNECTOR
CHART A-7
(Page 4 of 2)
FUEL SYSTEM DsAGNOSBS
2.8L (VIN S) ""FYSERBES (PORT)
Circuit Description:
When the ignition switch is turned "ON", the electronic control module (ECM) will turn "ON" the in-tank
fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving
HE1
distributor reference pulses.
If there are no reference pulses, the ECM will shut "OFF" the fuel pump within
2 seconds after key "ON" or
engine stopped.
The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system
pressure is controlled to about 234 to 317
kPa (34 to 46 psi). Excess fuel is then returned to the fuel tank.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Use pressure gage 5-34730-1. Wrap a shop towel
around the fuel pressure tap to absorb any small
amount of fuel leakage that
may occur when
installing the gage.
Ignition "ON", pump pressure should be 280-325
kPa (40.5-47 psi). This pressure is controlled by
spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure
is low (high vacuum) and is applied to the fuel
regulator diaphragm. This will offset the spring
and result in a lower fuel pressure.
'This idle
pressure will vary somewhat depending on
barometric pressure, however, the pressure idling
was less indicating pressure regulator control.
3. Pressure that continues to fall is caused by one of
the following:
In-tank fuel pump check valve not holding.
@ Pump coupling hose or pulsator leaking.
Fuel pressure regulator valve leaking.
@ Injector sticking open. 4.
An injector sticking open can best be determined
by checking for a fouled or saturated spark
plug(s).
If a leaking injector can not be determined by a
fouled or saturated spark plug the following
procedure should be used.
e Remove Plenum, cold start valve and remove
fuel rail bolts. Follow the procedures in the
fuel control section of this manual, but leave
fuel lines connected.
@ Reconnect cold start valve.
@ Connect a hose to valve nozzle and insert into
a gasoline container.
@ Lift fuel rail out just enough to leave injector
nozzles in the ports.
CAUTION: BE SURE INJEePOR(S) ARE NOT ALLOWED
PO SPRAY ON ENGINE AND THAT INJECTOR
RETAINING
CLIPS ARE INTACT. PHIS SHOULD BE
CAREFULLY
FOLLOWD PO PREVENT FUEL SPRAY ON'
ElZIGlNE WHICH WOULD CAUSE A FIRE HAZARD.
@ Pressurize the fuel system.
@ I.if't each side of rail up and observe for
injc~ctot-l.) It.ulting

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-A-19
THIS CHART ASSUMES THERE IS NO
CODE
54
'OFF' FOR 10 SECONDS. AIC "OFF". ,,. . . . . . . . .'.
"ON". FUEL PUMP WILL RUN FOR ABOUT 2 : FROM :
THE IGNITIONMAY HAVE TO BE : A-3 : CYCLED "ON" MORE THAN ONCE
TO OBTAIN MAXIMUM PRESSURE.
ALSO, IT IS NORMAL FOR THE
PRESSURE TO DROP SLIGHTLY
WHEN THE PUMP STOPS.
AT NORMAL OPERATING
TEMPERATURE.
IGNITION "ON"
@ IGNITION "OFF".
BLOCK FUEL PRESSURE @ APPLY 12 VOLTS LINE BY PINCHING FLEX
TO FUEL PUMP
HOSE. PRESSURE TEST TERMINAL.
@ IGNITION "OFF" FOR 10 @ APPLY 10 INCHES OF VACUUM
LEAKING PUMP COUPLING
TO PRESSURE REGULATOR. @ IGNITION "ON".
INLET FILTER.