1988 PONTIAC FIERO Service Repair Manual

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.

6E3-A-28 S.OL (VIN F) & 5.7L (VIN 8) DRIVEABILITY AND EMISSIONS
COOLANT SENSOR SIGNAL
CODE 15
COOLANT TEMPERATURE SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
5.OL (VIN F) & 5.7L (VIN 8) 'Ti' 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
95'0, the voltage will measure about 1.5 to 2.0 volts at the ECM.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 15 will set if:
@ signal voltage indicates a coolant temperature
less than
-44" C (-47" F) for 3 seconds.
2. This test simulates a Code 14. If the ECM
recognizes the low signal voltage, (high temp.)
and
the "Scan" reads 130°C or above, the ECM and
wiring are OK.
3. This test will determine if CKT 410 is open. There
should be 5 volts present at sensor connector if
measured with
a DVM.
Diagnostic Aids:
A "SCAN" tool reads engine temperature in
degrees centigrade. After engine is started the
temperature should rise steadily
to about 90°C then
stabilize when thermostat opens.
A faulty connection, or an open in CKT 410 or 452
will result in a Code 15.
If Code 22 or 23 is also set, check CKT 452 for faulty
wiring or connections. Check terminals at sensor for
good contact. Refer to "Intermittents" in Section
"R".

DRIVEABILITY AND EMISSIONS 5.0L (VIN F) & 5.7L (VIN 8) 6E3-A-29
COOLANT SENSOR
TEMPERATURE TO RESISTANCE VALUES
(APPROXIMATE)
"F "C OHMS
210 100 185
160 70 450
100 38 1,800
70 20 3,400
40 4 7,500
20
-7 13,500
0
-1 8 25,000
-40 -40 100,700
COOLANTTEMPERATURE SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED )
DIAGNOSTIC AID