PONTIAC FIERO 1988 Service Repair Manual

6E3-A-18 5.OL (WIN F) & 5.7L(VIN 8) DRIVEABILITY AND EMISSIONS
PRESSURE REGULATOR
COLD START
TUBE ASSEMBLY
FUEL PRESSURE
LINE
CHART A-7
(Page 1 of 2)
FUEL SYSTEM DIAGNOSIS
5.OL (VIN F) & 5.7L (VIN 8) 'TF'3SERlES (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
reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after
ignition "ON" or engine stops.
The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system
pressure is controlled at 234 to 325
kPa (34 to 47 psi). Excess fuel is then returned to the fuel tank.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Wrap a shop towel around the fuel pressure
connector 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
assenlbly
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
should be 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(s) 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 cannot be determined by a
fouled or saturated spark plug, the following
procedure should be used:
@ Remove Plenum, and remove fuel rail bolts.
Follow the procedures in the Fuel Control
Section of this manual, but leave fuel lines
connected.
s Lift fuel rail out just enough to observe
injector nozzles in the ports.
CAUTION: BE SURE INJECTOR(S) ARE NOT ALLOWED
TO SPRAY ON ENGINE AND THAT INJECTOR
RETAINING CLIPS ARE INTACT.
THIS SHOULD BE
CAREFULLY FOLLOWED TO PREVENT FUEL SPRAY ON
ENGINE WHICH WOULD CAUSE A
FIRE HAZARD.
@ Pressurize the fuel syste~rl and observe injector
nozzles.

: THIS CHART ASSUMES a CHART m THERE IS NO CODE 54
m PAGE 1.
THE IGNITION MA Y HA
VE TO BE CYCLED "ON"
RESSURE, WITH PUMP RUNNING SHOULD BE MORE
THAN ONCE TO OBTAIN MAXIMUM
(40.5-47 psi) AND HOLD STEADY WHEN PUMP PRESSURE.
ALSO, ITlS NORMAL FOR THE PRESSURE TO DROP SLIGHT1 Y WHEN THE PUMP STOPS.
10 SECONDS.
...... I
@ LEAKING PUMP
@ PLUGGED PUMP INLET FILTER.
RESTRICTED FUEL LINE.

TEST CONNECTOR PRESSURE REGULATOR
COLD START
VALVE AND
TUBE ASSEMBLY
FUEL PRESSURE
LINE
PUMP INLET FlLTE
CHART A-7
(Page 2 of 2)
FUEL SYSTEM DIAGNOSIS
5.OL (VIN F) & 5.7L (VIN 8) "F" SERIES (PORT)
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Fuel pressure less than 280 kPa (40.5 psi) falls
into two areas:
Regulated pressure less than
280 kPa
(40.5 psi) - Amount of fuel to injectors OK but
pressure is too low. System will be lean and
may set Code
44. Also, hard starting cold and
overall poor performance.
@ Restricted flow causing pressure drop -
Normally, a vehicle with a fuel pressure of less
than
165 kPa (24 psi) at idle will not be
driveable. However, if the pressure drop
occurs only while driving, the engine will
normally surge then stop running
as pressure
begins to drop rapidly. This is most likely
caused by
a restricted fuel line or plugged
filter.
2. Restricting the the fuel return line allows the fuel
pump to develop its maximum pressure (dead head
pressure). When battery voltage is applied to the
pump
tesl terminal, pressure should be above
414 kPa (60 psi ).
3. This test determines if the high fuel pressure is
due to
a restricted fuel return line or a pressure
regulator problem.

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) & 5.7L (VIN 8) 6E3-A-21
NOTICE: THE FUEL SYSTEM IS UNDER PRESSURE. TO AVOID FUEL SPILLAGE,
REFER TO FIELD SERVICE PROCEDURES IN SECTION
"C2" FOR TESTING
OR MAKING REPAIRS REQUIRING DISASSEMBLY OF FUEL LINES OR
.m ...... -
SE TO PRESSURE
@ BLOCK FUEL RETURN LINE.
@ APPLY 12 VOLTS TO FUEL PUMP RELAY
HARNESS TERMINAL "A" OR TO THE
FAULTY IN-TANK
r FUELPUMP
@ COUPLING HOSE OR

6E3-A-22 5.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COLD START SWITCH
CONNECTOR
CLOSED BELOW
3S°C.
8 SEC. TIME LIMIT
COOLANT
CHART A99
COLD START VALVE CIRCUIT TEST
5.OL (VIN F) & 5.7L (VIN 8) "F" SERIES (PORT)
Circuit Description:
The cold start valve is used to provide additional fuel cluring the crank mode to improve cold start-ups. This
circuit is important when engine coolant temperature is low because the other injectors are not pulsed
"ON"
long enough to provide the needed amount of fuel to start.
The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and
is protected by a fuse. The system is controlled by a cold start fuel injection switch which provides a ground path
for the valve during cranking when engine coolant is below 35°C (95°F).
The cold start fuel injection switch consists of a bimetal material which opens at a specified coolant
temperature. This bimetal is also heated by the winding in the thertnal switch which allows the valve lo stay
"ON" for 8 seconds at -20°C (-4°F) coolant. The time the switch will stay closed varies inversely with coolant
temperature. In other words, as the coolant temperature goes up, the cold start valve
"ON" time goes down.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Disconnecting the distributor 4-way connector
will disable the other injectors. The amount of
pressure drop depends on the temperature of the
engine. This test could also be performed
by
removing the two injector fuses.
2. This test will determine the continuity through
the switch to ground.

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) & 5.7L (VIN 8) 6E3-A-23

6E3-A-24 5.OL (VIN F) & 5.71 (VIN 8) DRIVEABILITY AND EMISSIONS
OXYGEN ( 02) SENSOR
CODE 13
OXYGEN SENSOR CIRCUIT
(OPEN CIRCUIT)
5.OL (VIN F) & 5.7L (VIN 8) 'T" SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D7" and "D6". (If measured with a 10
megohm digital voltmeter, this may read as low as .32 volts.) The
O2 sensor varies the voltage within a range
of about 1 volt if the exhaust is rich, down through about
.l0 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below 360
" C(60OoF). An open sensor
circuit or cold sensor causes "Open Loop" operation.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 13
WILL SET:
@ Engine at normal operating temperature
(above 70°C)
@ At least 2 minutes engine time after start.
@ O2 signal voltage steady between .35 and .55
volts.
@ Throttle position sensor signal above 5%.
(about
.3 volts above closed throttle voltage).
@ All conditions must be met for about 60
seconds. If the conditions for
a Code 13 exist, the
system will not go "Closed Loop".
2. This will determine if the sensor is at fault or the
wiring or ECM is the cause of the Code 13.
3. For this test use only a high impedance digital
voltohm meter. This test checks the continuity of
CKTs 412 and 413. If CKT 413 is open, the ECM
voltage on CKT 412 will be over .6 volts (600 mV).
Diagnostic Aids:
Normal "Scan" voltage varies between 1OOmV to
999mV (.1 and 1.0 volt) while in "Closed Loop". Code
13 sets in one minute if voltage remains between .35
and .55 volts, but the system will go
"Open Loop" in
about
15 seconds.
Refer to "Intermittents" in Section
"B".

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) €4 5.7L (VIN 8) 6E3-A-25
r RUN ENGINE ABOVE 1200 RPM FOR TWO MINUTES.
DOES "SCAN" INDICATE "CLOSED LOOP"?
JUMPER HARNESS
CKT412 TO GROUND.
00
mV) WITH ENGINE RUNNING.
SENSOR HARNESS CONNECTOR USING A DVM.
OVER
.6 VOLT LESS
THAN .3
FAULTY CONNECTION

6E3-A-26 5.OL (VIM F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COOLANT SENSOR SIGNAL
-
CODE 14
COOLANT TEMPERATURE SENSOR CIRCUIT
(HIGH TEMPERATURE INDICATED)
5.OL (VIN F) & 5.7L (VIN 8) "F"" SERIES (PORT)
Circuit Description:
The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM
applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high,
therefore, the ECM will see high signal voltage.
As the engine warms, the sensor resistance becomes less, and the voltage drops.
At normal engine operating
temperature
(85°C to 95"C), the voltage will measure about 1.5 to 2.0 volts.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 14 will set if:
@ signal voltage indicates a coolant temperature
above 130°C (266°F) for
3 seconds
2. This test will determine if CKT 410 is shorted to
ground which will cause the conditions for Code
14.
Diagnostic Aids:
Check harness routing for a potential short to
ground in
CKT 410.
"SCAN" tool displays engine temp, in degrees
centigrade. After engine is started, the temperature
should rise steadily to about
90°C, then stabilize when
thermostat opens.
Refer to "Intermittents" in Section
"B".

DRIVEABILITY AND EMISSIONS 5.0L (WIN F) & 5.7L (WIN 8) 6E3-A-27
DIAGNOSTIC AID
COOLANT SENSOR
TEMPERATURE TO RESISTANCE VALUES
(APPROXIMATE)
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.