PONTIAC FIERO 1988 Service Repair Manual

6EZ-A-40 5.0L (WIN E) DRIVEABILITY AND EMISSIONS
CODE 33
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE HIGH - LOW VACUUM)
5.OL (VIN E) "F" SERIES (TBI)
Circuit Description:
The manifold absolute pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The
ECM receives this information as a signal voltage that will vary from about
1-1.5 volts at idle to 4-4.5 volts at
wide open throttle.
A "Scan" displays manifold pressure in volts. Low pressure (high vacuum) reads
a low voltage while a high
pressure (low vacuum) reads a high voltage.
If the MAP sensor fails the ECM will substitute
a fixed MAP value and use the throttle position sensor
(TPS) to control fuel delivery.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 33 will set when:
@ Signal is too high, (kPa greater than 68 kPa),
for a time greater than 5 seconds.
-S TPS less than 4%.
Engine misfire or a low unstable idle may set Code
33. Disconnect MAP sensor and system will go
into backup mode. If the misfire or idle condition
remains, see "Symptoms" in Section "B".
2. If the ECM recognizes the low MAP signal, the
ECM and wiring are OK.
Diagnostic Aids:
An open in CKT 455 will result in a Code 33.
With the ignition "ON" and the engine stopped,
the manifold pressure is equal to atmospheric
pressure and the signal voltage will be high.
This
information is used by the ECM as an indication of
vehicle altitude
and is referred to as BARO.
Comparison of this
BARO reading with a known good
vehicle with the same sensor is a good way to check
accuracy of a "suspect" sensor. Reading should he the
same,
& .4 volt.
Also
CHART C-lD can be used to test the MAP
sensor.
Refer to
"Intermittnets" in Section "B".
If idle is rough or unstable refer to "Symptoms" in
Section
"B" for items which can cause an unstable
idle.

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-A-41
SENSOR VACUUM HOSE OR
Below 305 Below 1,000
305--- 61 0 1.000--2,000
610--- 91 4 2,000--3,000
91 4--1219 3.000--4,000
121 9--1524 4,000--5,000
1524--1829 5,000--6,000
1829--2133 6,000--7,000
21
33-2438 7,000--8,000
2438--2743 8,000--9,000
2743--3048 9,000--10,000

6EZ-A-42 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
CODE 34
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE LOW - HIGH VACUUM)
5.OL (VIN E) ""F-SERlES (TBI)
Circuit Description:
The manifold absolute pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The
ECM receives this information as a signal voltage that will vary from about 1-1.5 volts at idle to 4-4.5 volts at
wide open throttle.
If the MAP sensor fails the ECM will substitute a fixed MAP value and use the throttle position sensor
(TPS) to control fuel delivery.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 34 will set when:
e Signal is too low (kPa less than 14) and engine
running less than 1200 rpm.
OR
@ Engine running greater than 1200 rpm.
e Throttle position greater than 21% (over 1 5
volts).
2. If
the ECM recognizes the high hIAP signal, the
ECM and wiring are OK.
3. The "Scan" tool may not display 12 volts. The
important thing is that the ECM recognizes the
voltage as more than 4 volts, indicating that tho
ECM and CKT 432 are OK.
Diagnostic Aids:
An intermittent open in CKTs 432 or 416 will
result in a Code 34.
With the ignition "ON" and engine stopped, the
manifold pressure is equal to atmospheric pressure
and the signal voltage will be high. This information
is
used by the ECM as an indication of vehicle altitude
and is referred to as BARO. Comparison of this BARO
reading with a known good vehicle wilh the same
sensor is a good way to check accuracy of a "suspect"
sensor.
Iteading shoulci be the same, + .4 volts.
Refer to "Intermittnets" in Section "B".

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-A-43
CODE 34
MANlFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE LOW - HIGH VACUUM)
5.OL (VIN E) ""IF" SERIES (TBI)
ENSOR ELECTRICAL CONNECTOR.
ESS TERMINALS "B" PO "C".
SHOULD READ OVER 4 VOLTS.
AL
"B" (CKT432) WITH A
IGNITION "ON" ENGINE STOPPED VOLTAGES
Below 305 Below 1,000
305--- 610 1,000--2,000
61 0--- 91 4 2,000--3,000
91 4--1219 3,000--4,000
1219--1524 4,000--5,000
1524--1829 5,000--6,000
1829--2133 6,000--7,000
21
33-2438 7,000--8,000
2438--2743 8,000--9.000
2743--3048 9,000--10,000

6E2-A-44 5.OL (WIN E) DRIVEABILITY AND EMISSIONS
DISTRIBUTOR 4 TERM
CONNECTOR
DISTRIBUTOR
430 PPVWHT
424 TANIBLK
CODE 42
ELECTRONlC SPARK TIMING (EST) CIRCUIT
5.OL (VIN E) ""FYSERIES (TBI)
Circuit Description:
When the system is running on the ignition module, that is, no voltage on the by-pass line, the ignition
module grounds the EST signal. The ECM expects to see no voltage on the EST line during this condition. If it
sees a voltage, it sets Code 42 and will not go into the EST mode.
When the
rpm for EST is reached (about 400 rpm), and by-pass voltage applied, the EST should no longer be
grounded
i; the ignition module so the EST voltage should be varying.
If the by-pass line is open or grounded, the ignition module will not
switcli to EST mode so the EST voltage
will be low and Code 42 will be set.
If the EST line is grounded, the ignition module
will switch to EST, but because the line is grounded there
will be no EST signal.
A Code 42 will be set.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 42 means the ECM has seen an open or short
to ground in the EST or by-pass circuits. This test
confirms Code 42 and that the fault causing the
code is present.
2. Checks for a normal EST ground path through the
ignition module.
An EST CKT 423 shorted to
ground will also read less than 500 ohms.
however, this will be checked later.
3. As the test light voltage touches CKT 424, the
module should switch causing the ohmmeter
to
"overrange" if the meter is in the 1000-2000 ohnls
position. Selecting the 10-20,000 ohms position
will indicate
above 5000 ohms. The important
thing is that the moclul(~ ".;~vitched"
4. The module did not switch and this step checks for:
@ ES'I' CKT 423 shorted to ground.
@ By pass C KT 424 open.
@ Faulty ignition module connection or module.
5. Confirms that Code 42 is a faulty ECM and not an
intermittent in
CKTs 423 or 424.
Diagnostic Aids:
If a Code 42 was stored and the customer
complains of
a "IIard Start", the problem is most
likely a grounded EST line (CKT 423).
'I'he "Scan" tool does not have any ability to help
diagnose
a Code 42 problem.
rl PROM not Sully seated in the ECM can result in
Code 42
11~1'(.1- 10 '.In1 c.l.lnlt tc~nth" in Sectiotl "13".

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-A-45
IDLE ENGINE FOR 1 MINUTE OR UNTIL CODE 42 SETS.
PROBE ECM HARNESS CONNECTOR CKT
423 WITH AN

CODE 43
ELECTRONIC SPARK CONTROL (ESC) CIRCUIT
5.0L (VIN E) "F" SERIES (TBI)
Circuit Description:
Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the
knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the
ECM to retard timing. The ECM will retard the timing when knock is detected and rpm is above about 900
rpm. Code 43 means the ECM has been low voltage at CKT 485 terminal
"B7" for longer than 5 seconds with the
engine running or the system has failed the functional check.
This system performs a functional check once per start up to check the ESC system. To perform this test the
ECM will advance the spark when coolant is above 95°C and at
a high load condition (near W.O.T.). The ECM
then checks the signal at
"B7" to see if a knock is detected. The functional check is performed once per start up
and if knock is detected when coolant is below 95°C (194°F) the test has passed and the functional check will not
be run. If the functional check fails, the "Service Engine Soon" light will
remain "ON" until ignition is turned
"OFF" or until a knock signal is detected.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. If the conditions for a Code 43 are present the
"Scan" will always display "yes". There should
not be a knock at idle unless an internal engine
problem, or a system problem exists.
2. This test will determine if the system is
functioning at this time. Usually a
knock signal
can be generated by tapping on the block close to
the area of the sensor.
3. Because Code 43 sets when the signal voltage on
CKT 485 remains low this test should cause the
signal on CKT 485 to go high. The
12 volts signal
should be seen by the ECM as "no knock"
it' the
ECM and wiring are OK.
4.
This test will determine if the knock signal is
being detected on CKT 496 or if the ESC module is
at fault. 5.
If
CKT 496 is routed to close to secondary ignition
wires the ESC
module may see the interference as
a knock signal.
6. This checks the ground circuit to the module. An
open ground will cause the voltage on CKT 485 to
be about
12 volts which would cause the Code 43
functional test to fail.
7. Contacting
CKT 496 with a test light to
12 volts
should generate a knock signal.
This will
determine if the ESC nodule is operating
correctly.
Diagnostic Aids:
Code 43 can be caused by a faulty connection at
the knock sensor at the ESC
lnodule or at the ECM.
Also check CKT 485 for possible open or short to
ground.
Iiefer to "Intcrmittents" in Section "B".

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-A-47
IN AREA OF KNOCK SENSOR. 5 TERMINAL "C" (CKT
INDICATED WHILE TAPPING
ST LIGHT CONNECTED
AFTER
5 SECONDS, DOES "SCAN"
@ DISCONNECT KNOCK SENSOR.
ENGINE IDLING.
@ MOMENTARILY TOUCH KNOCK
SENSOR HARNESS (CKT496) WITH
A TEST LIGHTTO 12V. @ EACH TIME THE TEST LIGHT
CONTACTS CKT 496, A KNOCK

6E2-A-48 5.OL, (VIN E) DRIVEABILITY AND f MISSIONS
CODE 44
OXYGEN SENSOR CIRCUIT
(LEAN EXHAUST INDICATED)
5.OL (VIN E) "F" SERIES (TBI)
Circuit Description:
The ECM supplies a voltage of about .45 'volt between terminals "D6" and "117". (If measured with a 10
megohmdigital voltmeter, this may readas low as .32 volts.) The 02 sensor varies the voltage within a range of
about
1 volt if the exhaust is rich, down through about .I0 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about
360°C (600°F). 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 44 is set when the 02 sensor signal voltage
on
CK'l' 412.
@ Remains below .2 volt for 50 seconds,
@ And the system is operating in 'qClosk?d Loop". @
@
Diagnostic Aids:
Using the "Scan", observe the block learn values
at different rpm and air flow conditions to determine
@
when the Code 44 may have been set. If the
conditions for Code
44 exists the block learn values
will be around 150.
@ Q2 Sensor Wire Sensor pigtail may be
m?spositioned and contacting the exhaust @
manifold.
@ Check for intermittent ground in wire between
connector and sensor.
@
MAP Sensor A (MAP) sensor output that causes
the ECM to sense a higher than normal vacuum
will cause the
system to go lean. Disconnect the
MAP sensor and
if the lean condition is gone,
replace the sensor.
Lean
Iniectorts)
Fuel Contamination Water, even in small
amounts, near the in-tank fuel pump inlet can be
delivered to the injectors. The water causes
n lean
exhaust and can set a Code
44.
Fuel Pressure System will be lean if pressure is
too low.
It
may be necessary to monitor fuel
pressure while driving the car at various road
speeds
ancUor loads to confirm. See "Fuel System
Diagnosis",
CHART A-7.
Exhaust
Leaks If there is an exhaust leak, the
cngine can cause outside air to be pulled into the
eshaust
and past the sensor. Vacuum or
crankcase leaks can cause a lean condition.
If the above are OK, it is a faulty oxygen sensor.

@ WITH ENGINE IDLING "SCAN" SHOULD DISPLAY O2
SENSOR BETWEEN .35 VOLTS AND .55 VOLTS (350