1988 PONTIAC FIERO Service Repair Manual

6EZ-A-38 5.OL (VIN E) DRIVEABILITY AND EMISSIONS
TO EGR VALVE
CODE 32
EXHAUSWAS RECIRCULATION (EGR) CIRCUIT
5.OL (VIN E) "FF" SERIES (TBI)
Circuit Description:
The ECM operates a solenoid to
control the exhaust gas recirculation (EGR) valve. This solenoid is
normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass
to the EGR valve.
The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off
vacuum to the EGR valve diaphragm. With the EGR valve closed, manifold vacuum will be greater than it was
during normal EGR operation and this change will be relayed to the ECM by the MAP sensor. If the change is
not within the calibrated window, a Code
32 will be set.
The ECM will check EGR operation when:
@ Vehicle speed is above 50 mph.
@ Engine vacuum is between 40 and 51 kPa.
@ No change in throttle position while test is being run.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Checks for solenoid stuck open.
2. Checks for solenoid always being energized.
3. Grounding test terminal should energize solenoid
and vacuum should drop.
4. Negative backpressure valve should hold vacuum
with engine "OFF".
5. When engine is started, exhaust backpressure
should cause vacuum to bleed off and valve to fully
close.
6. 5.OL engines have a ~nanifold vacuum source
which should have at least
7" Hg at idle.
Diagnostic Aids:
Vacuum lines should be thoroughly checked for
internal restrictions. The ECM uses the MAP sensor
for checking EGR operation. If there is a question of
MAP sensor accuracy use
CHART C-1D MAP output
check in Section "C".
If no problems are found refer to "Intermittents"
in Section
"13".

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6EZ-A-39
BEFORE USING THIS CHART, CHECK FOR MANIFOLD VACUUM TO EGR
@ GROUND DIAGNOSTIC TERMINAL. @ INSTALL A HAND HELD VACUUM PUMP WITH GAGE TO MANIFOLD
PUMP TO EGR VALVE.
@ USING A MIRROR,
OBSERVE EGR
DIAPHRAGM WHILE
APPLYING VACUUM.
DIAPHRAGM SHOULD OR
TERMINALS.
MOVE FREELY AND "ON",
ENGINE "OFF".
HOLD VACUUM FOR AT T
SHOULD LIGHT.
LEAST
20 SECONDS.
OBSERVE VACUUM GAGE ON
VACUUM PUMP.
HAS MOVED TO SEATED POSITION
CLEAR CODES AND CONFIRM "CLOSED LOOP"
OP

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