1988 PONTIAC FIERO Service Repair Manual

6E3-A-44 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
NlnF RELAY CONN.
BATTERY
+ -,
I.P. HARNESS CONNECTOR IS WAY. (FRONTVIEW)
I.. . . . . . ., 1. EllCE
a
GAGE
902
TO EGR
& MAF RELAY 7-29-87 CCP SOLENOIDS MAF
SENSOR
ENG.
GND.
MAF SENSOR CONNECTOR
ECM
CODE 34
MASS AIR FLOW (MAF) SENSOR CIRCUIT
(GMISEC LOW)
2.8L (VIN 5) "F" SERIES (PORT)
Circuit Description:
The MAF sensor measures the flow of air entering the engine. The sensor produces a frequency output
between 32 and 150 hertz
(3grnfsec to 150gndsec). A large quantity (high frequency) indicates acceleration, and
a small quantity (low frequency) indicates deceleration or idle. This information is used by the ECM for fuel
control and is converted by a "SCAN" tool to read out the air flow in grams per second. A normal reading is
about 4-7 grams per second at idle and increase with rpm.
The MAF sensor is powered up by the MAF sensor relay and the sensor should have power supplied to it
anytime the ignition is "ON".
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
I. Code 34 will set if:
@ Engine running
@ MAF sensor disconnected, faulty relay, or
MAF signal circuit shorted to ground.
OR
@ Air flow less than 2 grams per second (low
frequency).
A loose or damaged air duct can set Code 34.
This test checks to see if ECM recognizes a
problem.
A light "OFF" at this point indicates an
intermittent problem.
2. Checks to see if 5 volt reference signal from ECM
is at MAF
sensor harness connector.
3. Checks for 12 volt supply to MAF sensor.
4. Checks for open in 12 volt supply to relay.
Diagnostic Aids:
The "Scan" tool is not of much use in diagnosing
this code because when the code sets
gdsec will be
displaying the default value. However, the "Scan"
may be useful in comparing the signal of a problem
vehicle with that of a known good running one.
Check for loose or damaged air duct.
Inspect sensor and relay connections as an open
will result in
a Code 34.
Refer to "Intermittents" in Section "B".

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-A-45
START AND IDLE ENGINE FOR 1 MINUTE OR
DISCONNECT MAF SENSOR ELECTRICAL CONNECTOR.
IGNITION "ON", ENGINE STOPPED.
CONNECT VOLTMETER BETWEEN HARNESS
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

6E3-A-$6 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
CODE 41
CYLINDER SELECT ERROR
2.8& (VIN S) "F" SERIES (PORT)
Circuit Description:
Due to the ECM being used for different engines, it is necessary for the engine application to be selected.
This is done by leaving
"R12" and "D3" open for a six cylinder engine.
A Code 41 will set if the reference pulses are not equal to a value selected within the PROM when engine
rpm's
are below 2000. This code may set if the incorrect PROM is installed into the ECM.

6E3-A-48 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
DISTRIBUTOR
CODE 42
ELECTRONIC SPARK TIMING (EST) FAULT
2.8L (VIN S) ""F3"lES (PORT)
Circuit Description:
When the system is running on the ignition module, that is, no voltage on the bypass 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 bypass voltage applied, the EST should on longer be
grounded in the ignition module so the EST voltage should be varying.
If the bypass line is open or grounded, the ignition module will not switch 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.
f est 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 bypass 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
oh~ns
position. Selecting the 10-20,000 ohms position
will indicate above 5000 ohms. The important
thing is that the
moclule "switched" 4.
The module did not switch and this step checks for:
s EST CKT 423 shorted to ground.
@ Bypass CKrI' 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:
The "Scan" tool does not have any ability to help
diagnose a Code 42 problem.
A PROM not fully seated in the ECM can result in
a Code 42.
Refer to "Intermittents" in Section "B".

BWlVEABlLlTV AND EMISSIONS 2.8L (VIN S) 6E3-A-49
OHMS RANGE.
R TO GROUND.
READ LESS THAN
500 OHMS.
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE
ENGINE SOON" LIGHT.

6E3-A-50 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
OXYGEN (02) SENSOR
-
CODE 44
OXYGEN SENSOR CIRCUIT
(LEAN EXHAUST INDICATED)
2.8L (VIN S) "F" "SERIES (PORT)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (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 .10 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 O2 sensor signal voltage
on CKT 412.
@ Remains below .2 volt for 60 seconds or more:
@ And the system is operating in "Closed Loop".
Diagnostic Aids:
Using the "Scan", observe the block learn values at
different rpm and air flow conditions. If the conditions
for Code 44 exists the block learn values will be
around 150.
@ -- 09 Sensor Wire Sensor pigtail may be
m~spositioned and contacting the exhaust
manifold.
@ Check for intermittent ground in wire between
connector and sensor.
@ MAF Sensor A mass air flow (MAF) sensor output
that causes the ECM to sense a lower than normal
air flow will cause the system to go lean.
Disconnect the MAF sensor and if the lean
condition is gone, check for a Code 34.
@ Lean Iniector(s) Perform injector balance test,
CHART C-2A.
@ Fuel Contamination Water, even in small
amounts, near the in-tank fuel pump inlet can be
delivered to the injectors. The water causes a 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
andlor loads to confirm. See "Fuel System
Diagnosis", CHART A-7.
@ Exhaust Leaks If there is an exhaust leak, the
engine can cause outside air to be pulled into the
exhaust and past the sensor. Vacuum or
crankcase leaks can cause a lean condition.
@ Air Systenl (manual trans only)
Be sure air is not being directed to the exhaust
ports while in "Closed Loop". If the block learn
value goes down while squeezing air hose to
exhaust ports, refer to CHART C-6.
@ If the above are OK, it is a faulty oxygen sensor.

DRIVEABILITY AND EMISSIONS 2.8L (VIN 5) 6E3-A-51
SENSOR BETWEEN .35 VOLTS AND .55 VOLTS (350
mV AND 550 mV).
CKT 412 SHORTED TO
GROUND OR FAULTY ECM.