1988 PONTIAC FIERO Service Repair Manual

6E3-A-52 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
- GROUND - -
CODE 45
OXYGEN SENSOR CIRCUIT
(RICH 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
02 sensor varies the voltage within a range of
about
1 volt if the exhaust is rich, down through about .LO volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about 315°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 45 is set when the
02 sensor signal voltage
or CKT 412.
@ Remains above .7 volt for 30 seconds; and in
"Closed LoopJ'.
@ Engine time after start is 1 minute or more.
@ Throttle less than 112 open but not at idle.
Diagnostic Aids:
Using the "Scan", observe the block learn values at
different rpm and air flow conditions. If the conditions
for Code 45 exists, the block learn values will be
around 1 15.
@ Fuel Pressure System will go rich if pressure is too
high. The ECM can compensate for some increase.
However, if it gets too high, a Code 45 may be set.
See "Fuel System Diagnosis", CHART A-7.
@ Rich Iniector Perform injector balance test CHART
C-2A.
@ Leaking Iniector See CHART A-7.
@ Check for fuel contaminated oil.
@ An open ground CKT 453 (ignition
system
reflow) may result in EMI, or induced
electrical "noise". The ECM looks at this "noise" as
reference pulses. The additional pulses result in a
higher than actual engine speed signal. The ECM
then delivers too much fuel, causing system to go
rich. Engine tachometer will also show higher than
actual engine speed, which can help in diagnosing
this problem.
@ Canister Purge Check for fuel saturation. If full of
fuel, check canister control and hoses. See
"Canister Purge", Section
"C3".
@ MAF Sensor An output that causes the ECM to
sense a higher than normal airflow can cause the
system to go rich. Disconnecting the MAF sensor
will allow the ECM to set
a fixed value for the
sensor. Substitute a different MAF sensor if the the
rich condition is gone while the sensor is
disconnected. Check for a Code 34.
@ Check for leaking fuel pressure regulator
diaphragm by checking vacuum line to regulator
for fuel.
@ TB An intermittent TPS output will cause the
system to go rich, due to a false indication of the
engine accelerating.
@ E]CR An EGR staying open (especially at idle) will
cause the
02 sensor to indicate a rich exhaust.

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-A-53
HARNESS CKT412 TO GROUND. IF
NO ADDITIONAL CODES WERE
0 "SCAN" SHOULD DISPLAY O2 BELOW STORED, REFER TO "DIAGNOSTIC
.35 VOLTS (350 mV).
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

BATTERY + PUMP SWI
439 PNWBLK
CODE 54
FUEL PUMP CIRCUIT
(LOW VOLTAGE)
2.8L (VIM S) ""FYSERIES (PORT)
Circuit Description:
The status of the fuel pump CKT 120 is monitored by the ECM at terminal "B2", and is used to compensate
fuel delivery based on system voltage. This signal is also used to store a trouble code if the fuel pump relay is
defective or fuel pump voltage is lost while the engine is running. There should be about
12 volts on CKT 120
for
2 seconds after the ignition is turned or any time references pulses are being received by the ECM.
Diagnostic Aids:
Code 54 will set if the voltage at terminal "U2" is
If a fault is detected during start-up the "Service
less than
2 volts for 1.5 seconds since the last reference Engine Soonw light will stay "ON" until the ignition is
pulse was received. This will help in detecting a cycled off. However, if the voltage is detected below 2
faulty relay, causing extended cranlc time and the volts with the engine running the light will only
code will help the diagnosis of an engine that remain on while the condition exists.
"CRANKS HUT WILL NOT RUN".

DRIVEABILITY AND EMISSIONS 2.8L (VIN 5) 6E3-A-55
FUSED JUMPER
ENGINE
IDLING AT NORMAL OPERATING

6E3-A-56 2.8L (VIN S) DRIVEABILITY AND EMISSIONS
PROM ERROR
(FAULTY OR INCORRECT PROM)
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.
CODE 53
SYSTEM OVER VOLTAGE
@ CODE 53 WILL SET IF VOLTAGE AT ECM TERMINAL "82" IS GREATER THAN 17.1 VOLTS FOR 2 SECONDS.
@ CHECK AND REPAIR CHARGING SYSTEM. SEE SECTION "6D".
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.
CODE 55
CLEAR CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NO "SERVICE ENGINE SOON" LIGHT.

BRIVEABILIW AND EMISSIONS 2.8L (VlN 9) 6E3-B-1
SECTION B
SYMPTOMS
"TABLE OF CONTENTS
............................................................. Before Starting Page B-l
lntermittents............................................................... PageB-2
HardStart......,.......................................................... PageB-2
...................................................... Hesitation, Sag, Stumble Page 8-3
....................................................... Surges and/or Chuggle Page B-3
.............................................. Lack of Power, Sluggish, or Spongy Page B-4
...................................................... DetonationISpark Knock
Page 8-4
.................................... .................... Cuts Out, Misses ..O Page €3-5
Backfire............,...................................................... Page8-5
.......................................................... Poor Fuel Economy Page B-6
........................................................... Dieseling, Run-on. Page 8-6
........................................ Rough, Unstable, or Incorrect Idle, Stalling Page B-6
............................................. Excessive
Exhaust Emissions or Odors Page B-7
....................................... Restricted Exhaust
System Check (Chart 6-1) Page 8-8
BEFORE STARTING
Before using this section you should have
performed the DIAGNOSTIC CIRCUIT CHECK
and found out that:
1. The ECM and "Service Engine Soon" light are
operating.
2. There are no trouble codes stored, or there is a
trouble code but no "Service Engine Soon" light.
Verify the customer complaint, and locate the
correct SYMPTOM below. Check the items
indicated under that symptom.
If the ENGINE CRANKS BUT
WILL NOT
RUN, see CHART
A-3.
Several of the symptom procedures below call
for a careful visual check. This check should
include: ECM
grounds for being clean and tight.
@ Vacuum hoses for splits, kinks, and proper
connections, as shown on Emission Control
Information label.
@ Air leaks at throttle body mounting and intake
manifold.
@ Air leaks between MAF sensor and throttle
body.
Ignition wires for cracking, hardness, proper
routing, and carbon tracking.
@ Wiring for proper connections, pinches, and cuts.
The importance of this step cannot be stressed
too strongly
- it can lead to correcting a problem
without further checks and can save valuable time.

6E3-B-2 2.8L (VIN 5) DRIVEABILITY AND EMISSIONS
Problem may or may not turn "ON" the "Service Engine SoonJ' light, or store a code.
DO NOT use the trouble code charts in Section
"A" for intermittent problems. The fault must be
present to locate the problem. If a fault is
intermittent, use of trouble code charts may result
in replacement of good parts.
@ Most intermittent problems are caused by
faulty electrical connections or wiring. Perform
careful check as described at start of Section
"B". Check for:
@ Poor mating of the connector halves, or
terminals not fully seated in the connector
body (backed out).
@ Improperly formed or damaged terminals.
All connector terminals in problem circuit
should be carefully reformed to increase
contact tension.
@ Poor terminal to wire connection. This
requires removing the terminal from the
connector body to check. See "Introduction"
to Section
"6E".
@ If a visual check does not find the cause of the
problem, the car can be driven with a voltmeter
connected to a suspected circuit. A "Scan" tool
can also be used for monitoring input signals to
the ECM to help detect intermittent conditions.
An abnormal voltage, or "Scan" reading, when
the problem occurs, indicates the problem may
be in that circuit. If the wiring and connectors
check OK and a trouble code was stored for a
circuit having a sensor, except for Codes
43, 44,
and 45, substitute a known good sensor and
recheck. An
intermittent "Service Engine Soon" light
with no stored code may be caused by:
@ Ignition coil shorted to ground and arcing at
spark plug wires or plugs.
@ "Service Engine Soon" light wire to ECM
shorted to ground. (CKT 419).
@ Diagnostic "Test" terminal wire to ECM,
shorted to
ground.(CKT 451)
@ ECM power grounds. See ECM wiring
diagrams.
@ Loss of trouble code memory. To check,
disconnect TPS and idle engine until "Service
Engine Soon" light comes "ON". Code
22 should
be stored, and kept in memory when ignition is
turned "OFF". If not, the ECM is faulty.
@ Check for an electrical system interference
caused by a defective relay, ECM driven
solenoid, or switch. They can cause
a sharp
electrical surge. Normally, the problem will
occur when the faulty component is operated.
@ Check for improper installation of electrical
options, such as lights, 2-way radios, etc.
@ EST wires should be kept away from spark plug
wires, distributor wires, distributor housing,
coil, and generator. Wire from ECM to
distributor (CKT
453) should be a good
connection.
@ Check for open diode across A/C compressor
clutch, and for other open diodes (see wiring
diagrams).
HARD START
Definition: Engine cranks OK, but does not start for a long
time. Does eventually run, or may start hut immediately dies.
@ Perform careful check as described at start of -
Section "B".
@ Make sure driver is using correct starting
procedure.
@ CHECK:
- TPS for sticking or binding or a high TPS
voltage with the throttle closed (should read
less than
,700 volts).
- High resistance in coolant sensor circuit or
sensor itself. See Code 15 chart or with
a.
"Scan" tool compare coolant temperature with
ambient temperature on
a cold engine. 8
- Fuel pressure CHART A-7. Water contaminated
fuel.
EGR operation. Be sure valve seats properly and
is not staying open. See CHART C-7.
Both injector fuses (visually inspect).
Ignition system
- Check distributor for:
Proper output with ST-125.
Worn shaft.
Bare and shorted wires.
Pickup coil resistance and connections.
Loose ignition coil ground.
Moisture in distributor cap.
If problem exists in cold weather, check cold start
valve. See CHART A-9.

DRIVEABILITY AND EMISSIONS 2.8L (VIN S) 6E3-B-3
e A faulty in-tank fuel pump check valve will @ If engine starts but then immediately stalls,
allow the fuel in the lines to drain back to the open
distributor by-pass line. If engine then
tank after the engine is stopped. To check for starts
and runs OK, replace pickup coil.
this condition:
@ If engine starts and stalls, disconnect MAF
Perform Fuel System Diagnosis, CHART A-7. sensor. If engine then runs and sensor
@ Remove spark plugs. Check for wet plugs, connections are OK, replace the sensor.
cracks, wear, improper gap, burned
f lectrodes,
or heavy deposits. Repair or replace as
necessary.
HESITATION, SAG, STUMBLE
Definition: Momentary lack of response as the accelerator is pushed down. Can
occur at all car speeds.
Usually most severe when first trying to make the car move, as
from a stop sign. May cause the engine to stall if severe enough.
Perform careful visual check as described at
start of Section
"B".
a CHECK:
- Fuel pressure. See CHART A-7. Also check for
water contaminated fuel.
- Air leaks at air duct between MAF sensor and
throttle body.
- Spark plugs for being fouled or faulty wiring.
- PROM (2.8L) or MEM-CAL (5.OL & 5.7L)
number. Also check service bulletins for latest
MEM-CAL or PROM.
- TPS for binding or sticking. Voltage should
increase at a steady rate as throttle is moved
toward WOT.
- Ignition timing. See Emission Control
Information label.
- Generator output voltage. Repair if less than 9
or more than 16 volts.
- HE1 ground, CKT 453.
- Canister purge system for proper operation.
See CHART C-3.
- EGR - See CHART C-7.
@ Perform injector balance test CHART C-2A.
SURGES AND/OR CHUGGLE
Definition: Engine power variation under steady
throttle or cruise. Feels like the car speeds up and
slows down with no change in the accelerator pedal.
Be sure driver understands transmission
converter clutch and
A/C compressor operation
in Owner's Manual.
e Perform careful visual inspection as described
at start of Section
"B".
CHECK:
- TCC and 4th gear switch operation - See
CHART C-8A.
- Loose or leaking air duct between MAF sensor
and throttle body.
- Generator output voltage. Repair if less than 9
or more than 16 volts.
- EGR - There should be no EGR at idle. See
CHART C-7. Also check for plugged EGR
solenoid filter.
- Vacuum lines for kinks or leaks.
- Ignition timing. See Emission Control
Information label.
- In-line fuel filter. Replace ifdirty or plugged.
- Fuel pressure while condition exists. See
CHART A-7.
@ Inspect oxygen sensor for silicone contamination
from fuel, or use of improper RTV sealant. The
sensor may have a white, powdery coating and
result in a high but false signal voltage (rich
exhaust indication). The ECM will then reduce
the amount of fuel delivered to the engine,
causing a severe driveability problem.
@ Remove spark plugs. Check for cracks, wear,
improper gap, burned electrodes, or heavy
deposits. Also check condition of distributor cap,
rotor, and spark plug wires.
@ To help determine if the condition is caused by a
rich or lean system, the car should be driven at
the speed of the complaint. Monitoring block
learn at the complaint speed will help identify the
cause of the problem. If the system is runnig lean
(block learn greater than
138), refer to
"Diagnostic Aids" on
facing page of Code 44. If
the system is running rich (block learn less than
118), refer to "Diagnostic Aids" on facing page of
Code 45.