width CHEVROLET DYNASTY 1993 User Guide

shutter. The switch plate contains the distributor
pick-up which is a Hall Effect device and magnet.
The shutter blades rotate through the distributor
pick-up. As the shutter blades pass through the pick-
up, they interrupt the magnetic field. The Hall effect
device in the pick-up senses the change in the mag-
netic field and switches on and off (which creates
pulses), generating the input signal to the PCM. The
PCM calculates engine speed through the number of
pulses generated.
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM INPUT
The PCM supplies 5 volts to the MAP sensor. The
MAP sensor converts intake manifold pressure into
voltage. The PCM monitors the MAP sensor output
voltage. As vacuum increases, MAP sensor voltage
decreases proportionately. Also, as vacuum decreases,
MAP sensor voltage increases proportionately. During cranking, before the engine starts running,
the PCM determines atmospheric air pressure from
the MAP sensor voltage. While the engine operates,
the PCM determines intake manifold pressure from
the MAP sensor voltage. Based on MAP sensor voltage and inputs from
other sensors, the PCM adjusts spark advance and
the air/fuel mixture. The MAP sensor mounts on the dash panel (Fig. 5).
A vacuum hose connects the sensor to the throttle
body.
HEATED OXYGEN SENSOR (O2SENSOR)ÐPCM
INPUT
The O2sensor is located in the exhaust manifold
and provides an input voltage to the PCM. The input
tells the PCM the oxygen content of the exhaust gas
(Fig. 6). The PCM uses the information to fine tune
the air-fuel ratio by adjusting injector pulse width. The O
2sensor produces voltages from 0 to 1 volt,
depending upon the oxygen content of the exhaust
gas. When a large amount of oxygen is present
(caused by a lean air-fuel mixture), the sensor pro-
duces a low voltage. When there is a lesser amount
present (rich air-fuel mixture), it produces a higher
voltage. By monitoring the oxygen content and con-
verting it to electrical voltage, the sensor acts as a
rich-lean switch. The oxygen sensor is equipped with a heating ele-
ment that keeps the sensor at proper operating tem-
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the
system to enter into closed loop operation sooner.
Also, it allows the system to remain in closed loop
operation during periods of extended idle. In Closed Loop operation the PCM monitors the O
2
sensor input (along with other inputs) and adjusts
the injector pulse width accordingly. During Open
Loop operation the PCM ignores the O
2sensor input.
The PCM adjusts injector pulse width based on a pre-
programmed (fixed) oxygen sensor input value and
inputs from other sensors.
SPEED CONTROLÐPCM INPUT
The speed control system provides four separate
voltages (inputs) to the PCM. The voltages corre-
spond to the On/Off, Set, and Resume. The speed control ON voltage informs the PCM
that the speed control system has been activated.
The speed control SET voltage informs the PCM that
a fixed vehicle speed has been selected. The speed
control RESUME voltage indicates the previous fixed
speed is requested. The speed control OFF voltage
tells the PCM that the speed control system has de-
activated. Refer to Group 8H for further speed con-
trol information.
Fig. 5 Manifold Absolute Pressure (MAP) Sensor Location
Fig. 6 Heated Oxygen Sensor
Ä FUEL SYSTEMS 14 - 27

TRANSAXLE PARK/NEUTRAL SWITCHÐPCM
INPUT
The park/neutral switch is located on the auto-
matic transaxle housing (Fig. 7). Manual transaxles
do not use park neutral switches. The switch pro-
vides an input to the PCM. The input indicates
whether the automatic transaxle is in Park, Neutral,
or a drive gear selection. This input is used to deter-
mine idle speed (varying with gear selection), fuel in-
jector pulse width, and ignition timing advance. The
park neutral switch is sometimes referred to as the
neutral safety switch.
THROTTLE POSITION SENSOR (TPS)ÐPCM INPUT
The Throttle Position Sensor (TPS) is mounted on
the throttle body and connected to the throttle blade
shaft (Fig. 8). The TPS is a variable resistor. The
sensor provides an input signal (voltage) to the PCM
representing throttle blade position. As the position
of the throttle blade changes, the resistance of the
TPS changes.
The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
PCM) represents the throttle blade position. The
PCM receives an input signal voltage from the TPS
varying in an approximate range of from 1 volt at
minimum throttle opening (idle) to 4 volts at wide open throttle. Along with inputs from other sensors,
the PCM uses the TPS input to determine current
engine operating conditions. The PCM adjusts fuel
injector pulse width and ignition timing based on
these inputs.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor is located in the transaxle
extension housing (Fig. 9). The sensor input is used
by the PCM to determine vehicle speed and distance
traveled.
The speed sensor generates 8 pulses per sensor rev-
olution. These signals, along with a closed throttle
signal from the TPS, determine if a closed throttle
deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.
AIR CONDITIONING (A/C) CLUTCH RELAYÐPCM
OUTPUT
The PCM operates the air conditioning clutch relay
ground circuit. The radiator fan relay supplies bat-
tery power to the solenoid side of the A/C clutch re-
lay. The air conditioning clutch relay will not
energize unless the radiator fan relay energizes. The
PCM energizes the radiator fan relay when the air
conditioning or defrost switch is put in the ON posi-
tion and the low pressure and high pressure switches
close. With the engine operating, the PCM cycles the air
conditioning clutch on and off when the A/C switch
closes with the blower motor switch in the on posi-
tion. When the PCM senses low idle speeds or wide
open throttle through the throttle position sensor, it
de-energizes the A/C clutch relay. The relay contacts
open, preventing air conditioning clutch engagement.
Fig. 7 Park/Neutral Switch
Fig. 8 Throttle Position Sensor
Fig. 9 Vehicle Distance (Speed) SensorÐTypical
14 - 28 FUEL SYSTEMS Ä

FUEL INJECTORÐPCM OUTPUT
The Fuel Injector is an electric solenoid operated
by the PCM (Fig. 15).
Based on sensor inputs, the PCM determines when
and how long the fuel injector should operate. The
amount of time the injector fires is referred to as in-
jector pulse width. The auto shutdown (ASD) relay
supplies battery voltage to the injector. The PCM
supplies the ground path. By switching the ground
path on and off, the PCM adjusts injector pulse
width. When the PCM supplies a ground path, a
spring loaded needle or armature lifts from its seat.
Fuel flows through the orifice and deflects off the
sharp edge of the injector nozzle. The resulting fuel
sprays forms a 45É cone shaped pattern before enter-
ing the air stream in the throttle body. Fuel is supplied to the injector constantly at regu-
lated 270 Kpa (39 psi). Unused fuel returns to the
fuel tank.
GENERATOR FIELDÐPCM OUTPUT
The PCM regulates the charging system voltage
within a range of 12.9 to 15.0 volts. Refer to Group
8A for charging system information.
IGNITION COILÐPCM OUTPUT
The PCM provides a ground contact (circuit) for en-
ergizing the ignition coil. When the PCM breaks the
contact, the energy in the coil primary transfers to
the secondary causing the spark. The PCM will de-
energize the ASD relay if it does not receive an input
from the distributor pick-up. Refer to Auto Shutdown
(ASD) Relay/Fuel Pump RelayÐPCM Output in this
section for relay operation. The ignition coil is mounted on the hot box next to
the thermostat housing (Fig. 16).
PART THROTTLE UNLOCK SOLENOIDÐPCM
OUTPUT
Three-speed automatic transaxles use a part throt-
tle unlock solenoid. The PCM controls the lock-up of
the torque convertor through the part throttle unlock
solenoid. The transaxle is locked up only in direct
drive mode. Refer to Group 21 for transaxle informa-
tion.
RADIATOR FAN RELAYÐPCM OUTPUT
The radiator fan is energized by the PCM through
the radiator fan relay. The PCM grounds the radia-
tor fan relay when engine coolant reaches a predeter-
mined temperature. For more information, refer to
Group 7, Cooling Systems. On AC, AG and AJ models, the radiator fan relay
is located in the power distribution center. Refer to
the Wiring and Component Identification section of
Group 8W. On AA and AP models, the radiator fan relay is
mounted on the drivers side fender well, next to the
strut tower (Fig. 10).
SPEED CONTROL SOLENOIDSÐPCM OUTPUT
The speed control vacuum and vent solenoids are
operated by the PCM. When the PCM supplies a
ground to the vacuum and vent solenoids, the speed
control system opens the throttle blade. When the
PCM supplies a ground only to the vent solenoid, the
throttle blade holds position. When the PCM removes
the ground from both the vacuum and vent solenoids,
the throttle blade closes. The PCM balances the two
solenoids to maintain the set speed. Refer to Group
8H for speed control information.
Fig. 15 Fuel Injector
Fig. 16 Ignition Coil
Ä FUEL SYSTEMS 14 - 31

TACHOMETERÐPCM OUTPUT
The PCM supplies engine RPM to the instrument
panel tachometer. Refer to Group 8 for tachometer
information.
MODES OF OPERATION
As input signals to the PCM change, the PCM
adjusts its response to the output devices. For example,
the PCM must calculate a different injector pulse
width and ignition timing for idle than it does for wide
open throttle (WOT). There are several different modes
of operation that determine how the PCM responds to
the various input signals. There are two different areas of operation, OPEN
LOOP and CLOSED LOOP. During OPEN LOOP modes, the PCM receives input
signals and responds according to preset PCM pro-
gramming. Input from the oxygen (O
2) sensor is not
monitored during OPEN LOOP modes. During CLOSED LOOP modes, the PCM does moni-
tor the oxygen (O
2) sensor input. This input tells the
PCM if the calculated injector pulse width results in an
air-fuel ratio of 14.7 to 1. By monitoring the exhaust
oxygen content, the can PCM fine tune injector pulse
width for optimum fuel economy and low emissions. The single point fuel injection system has the follow-
ing modes of operation:
² Ignition switch ON - Zero RPM
² Engine start-up
² Engine warm-up
² Cruise (Idle)
² Acceleration
² Deceleration
² Wide Open Throttle
² Ignition switch OFF
The engine start-up (cranking), engine warm-up, and
wide open throttle modes are OPEN LOOP modes. The
acceleration, deceleration, and cruise modes, with the
engine at operating temperature are CLOSED
LOOP modes (under most operating conditions).
IGNITION SWITCH ON (ZERO RPM) MODE
When the single point fuel injection system is acti-
vated by the ignition switch, the following actions
occur:
² The PCM determines atmospheric air pressure from
the MAP sensor input to calculate basic fuel strategy.
² The PCM monitors the coolant temperature sensor
and throttle position sensor inputs. The PCM modifies
fuel strategy based on these inputs. When the key is in the ON position and the engine is
not running, the (ASD) and fuel pump relays are not
energized. Therefore, battery voltage is not supplied to
the fuel pump, ignition coil, fuel injector or oxygen
sensor heating element. ENGINE START-UP MODE
This is an OPEN LOOP mode. The following actions
occur when the starter motor is engaged. If the PCM receives a distributor signal it energizes
the auto shutdown (ASD) relay and fuel pump relay to
supply battery voltage to the fuel injector, ignition coil
and oxygen sensor heating element. If the PCM does
not receive a distributor input, it de-energizes the ASD
and fuel pump relays after approximately one second. When the engine idles within 664 RPM of the target
RPM, the PCM compares the current MAP value with
the atmospheric pressure value it received during the
Ignition Switch On (Zero RPM) Mode. If a minimum
difference between the two is not detected, a MAP
sensor fault is set into memory. Once the ASD relay and fuel pump relay have ener-
gized, the PCM:
² Supplies a ground path to the injector. The injector
is pulsed four times per engine revolution instead of
the normal two pulses per revolution.
² Determines injector pulse width based on coolant
temperature, MAP sensor input, throttle position, and
the number of engine revolutions since cranking was
initiated.
² Monitors the coolant temperature sensor, distribu-
tor pick-up, MAP sensor, and throttle position sensor to
determine correct ignition timing.
ENGINE WARM-UP MODE
This is a OPEN LOOP mode. The following inputs
are received by the PCM:
² coolant temperature
² manifold absolute pressure (MAP)
² engine speed (distributor pick-up)
² throttle position
² A/C switch
² battery voltage
The PCM provides a ground path for the injector to
precisely control injector pulse width (by switching the
ground on and off) and fires the injector twice per
engine revolution. The PCM regulates ignition timing.
It also adjusts engine idle speed through the idle air
control motor.
CRUISE OR IDLE MODE
When the engine is at operating temperature this is
a CLOSED LOOP mode. During cruising speed and at
idle the following inputs are received by the PCM:
² coolant temperature
² manifold absolute pressure
² engine speed
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
14 - 32 FUEL SYSTEMS Ä

The PCM provides a ground path for the injector to
precisely control injector pulse width and fires the in-
jector twice per engine revolution. The PCM controls
engine idle speed and ignition timing. The PCM con-
trols the air/fuel ratio according to the oxygen con-
tent in the exhaust gas.
ACCELERATION MODE This is a CLOSED LOOP mode. The PCM recog-
nizes an abrupt increase in throttle position or MAP
pressure as a demand for increased engine output
and vehicle acceleration. The PCM increases injector
pulse width in response to increased fuel demand.
DECELERATION MODE This is a CLOSED LOOP mode. During decelera-
tion the following inputs are received by the PCM:
² coolant temperature
² manifold absolute pressure
² engine speed
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
The PCM may receive a closed throttle input from
the throttle position sensor (TPS) at the same time it
senses an abrupt decrease in manifold pressure from
the manifold absolute pressure (MAP) sensor. This
indicates a hard deceleration. The PCM may reduce
injector firing to once per engine revolution. This
helps maintain better control of the air-fuel mixture
(as sensed through the O
2sensor).
During a deceleration condition, the PCM grounds
the exhaust gas recirculation transducer (EET) sole-
noid. EGR stops when the PCM grounds the solenoid.
WIDE OPEN THROTTLE MODE This is an OPEN LOOP mode. During wide open
throttle operation, the following inputs are received
by the PCM:
² coolant temperature
² manifold absolute pressure
² engine speed
² throttle position
When the PCM senses a wide open throttle condi-
tion through the throttle position sensor (TPS) it
will:
² De-energize the air conditioning relay. This dis-
ables the air conditioning system.
² Provide a ground path for the electric EGR trans-
ducer (EET) solenoid, preventing the EGR system
from functioning. The exhaust gas oxygen content input is not ac-
cepted by the PCM during wide open throttle opera- tion. The PCM will adjust injector pulse width to
supply a predetermined amount of additional fuel.
IGNITION SWITCH OFF MODE
When the ignition switch is turned to the OFF po-
sition, the following occurs:
² All outputs are turned off.
² No inputs are monitored.
² The PCM shuts down.
FUEL PRESSURE REGULATOR
The pressure regulator is a mechanical device lo-
cated at the top of the throttle body (Fig. 17). Its
function is to maintain a constant 270 kPa (39 PSI)
across the fuel injector tip.
The regulator uses a spring loaded rubber dia-
phragm to uncover a fuel return port. When the fuel
pump becomes operational, fuel flows past the injec-
tor into the regulator, and is restricted from flowing
any further by the blocked return port. When fuel
pressure reaches 270 kPa (39 PSI) it pushes on the
diaphragm, compresses the spring, and uncovers the
fuel return port. The diaphragm and spring con-
stantly move from an open to closed position keeping
fuel pressure consistent.
THROTTLE BODY
The throttle body assembly (Fig. 18) is mounted on
top of the intake manifold. It contains the fuel injec-
tor, pressure regulator, throttle position sensor and
idle air control motor. Air flow through the throttle
body is controlled by a cable operated throttle blade
located in the base of the throttle body. The throttle
body itself provides the chamber for metering, atom-
izing, and mixing fuel with the air entering the en-
gine.
Fig. 17 Fuel Pressure Regulator
Ä FUEL SYSTEMS 14 - 33

² Methanol Concentration Sensor
² Pressure relief/Rollover valve
² PCV Valve
² All fuel system and emission system hoses and
tubes
SYSTEM OPERATION
The flexible fuel vehicle's 2.5L engine use a se-
quential multi-port electronic fuel injection system
(Fig. 1). The powertrain control module (PCM) oper-
ates the electronic fuel injection system. The PCM
provides precise air/fuel ratios and ignition timing
for all driving conditions.
The PCM regulates the air-fuel ratio, ignition coil
dwell and idle speed. The PCM also operates the
high speed and low speed cooling fans, charging sys-
tem, speed control system and various emission con-
trol devices. Various sensors and switches provide inputs to the
PCM. The PCM converts all inputs into signals and
regulates various systems based on the inputs. The
PCM adjusts the systems it controls to meet chang-
ing operating conditions. Fuel is injected into the intake port above the in-
take valve in precise metered amounts through elec-
trically operated injectors. The PCM operates the
injectors in a specific sequence. The PCM adjusts the
air/fuel ratio based on the percentage of methanol in the fuel. The PCM constantly adjusts injector pulse
width to obtain the ideal air fuel ratio for the current
percentage of methanol in the fuel. Injector pulse
width refers to the amount of time an injector oper-
ates. The PCM adjusts injector pulse width by opening
and closing the ground path to the injectors. Engine
RPM (speed), manifold absolute pressure (air density)
and the percentage of methanol in the fuel are the
primary inputs that determine injector pulse width.
SYSTEM DIAGNOSIS
The powertrain control module (PCM) can test
many of its own input and output circuits. If the
PCM senses a fault in a major system, the PCM
stores a diagnostic trouble code in memory. Technicians can display stored diagnostic trouble
codes by two different methods. The first is to cycle
the ignition switch On - Off - On - Off - On within 5
seconds. Then count the number of times the mal-
function indicator lamp (check engine lamp) on the
instrument panel flashes on and off. The number of
flashes represents the trouble code. There is a slight
pause between the flashes representing the first and
second digits of the code. Longer pauses separate in-
dividual trouble codes.
Fig. 1 Flexible Fuel MPI Components
14 - 56 FUEL SYSTEMS Ä

The second method of reading diagnostic trouble
codes uses the DRBII scan tool. For diagnostic trou-
ble code information, refer to the On-Board Diagnos-
tics section in this group.
CCD BUS
Various modules exchange information through a
communications port called the CCD Bus. The pow-
ertrain control module transmits vehicle load data on
the CCD Bus.
POWERTRAIN CONTROL MODULE
The powertrain control module (PCM) is a digital
computer containing a microprocessor (Fig. 2). The
PCM receives input signals from various switches
and sensors referred to as Powertrain Control Mod-
ule Inputs. Based on these inputs, the PCM adjusts
various engine and vehicle operations through de-
vices referred to as Powertrain Control Module Out-
puts.
PCM Inputs:
² Air Conditioning Controls
² Battery Voltage
² Brake Switch
² Engine Coolant Temperature Sensor
² Camshaft Position Sensor (Distributor Pick-up)
² Manifold Absolute Pressure (MAP) Sensor
² Methanol Concentration Sensor
² Oxygen Sensor
² SCI Receive
² Speed Control System Controls
² Throttle Position Sensor
² Park/Neutral Switch (automatic transaxle)
² Vehicle Speed Sensor
PCM Outputs:
² Air Conditioning Clutch Relay
² Generator Field
² Auto Shutdown (ASD) Relay
² Duty Cycle EVAP Canister Purge Solenoid
² Data Link (Diagnostic) Connector ²
Fuel Injectors
² Idle Air Control Motor
² Ignition Coil
² Malfunction Indicator (Check Engine) Lamp
² Radiator Fan Relay
² Speed Control Solenoids
² Tachometer Output
² Torque Converter Clutch Solenoid
Based on inputs it receives, the PCM adjusts fuel
injector pulse width, idle speed, ignition spark ad-
vance, ignition coil dwell and canister purge opera-
tion. The PCM regulates operation of the radiator
fan, A/C and speed control systems. Also, the PCM
changes generator charge rate by adjusting the gen-
erator field. The PCM adjusts injector pulse width (air-fuel ra-
tio) based on the following inputs.
² Battery voltage
² Coolant temperature
² Exhaust gas content
² Engine speed
² Manifold absolute pressure
² Methanol percentage of fuel
² Throttle position
The PCM adjusts ignition timing based on the fol-
lowing inputs.
² Coolant temperature
² Engine speed
² Manifold absolute pressure
² Methanol percentage of fuel
² Throttle position
The auto shutdown (ASD) and fuel pump relays are
mounted externally. The PCM turns both relays on
and off through the same circuit. The camshaft position sensor (distributor pick-up)
sends a signal to the PCM. If the PCM does not re-
ceive a camshaft position sensor signal within ap-
proximately one second of engine cranking, it
deactivates the ASD and fuel pump relays. When
these relays deactivate, they shut off power to the
fuel injectors, fuel pump, ignition coil, methanol con-
centration sensor and oxygen sensor heater element. The PCM contains a voltage converter that
changes battery voltage to a regulated 8.0 volts to
power the distributor pick-up methanol concentration
sensor and vehicle speed sensor. The PCM also pro-
vides a 5.0 volts supply for the engine coolant tem-
perature sensor, manifold absolute pressure sensor
and throttle position sensor.
AIR CONDITIONING SWITCH SENSEÐPCM INPUT
When the operator puts the A/C or defrost switch
in the ON position and the low pressure and high
pressure switches close, the PCM receives an input.
The input indicates the operator selected air condi-
tioning. After receiving this input, the PCM acti-
vates the A/C compressor clutch by grounding the
Fig. 2 Powertrain Control Module
Ä FUEL SYSTEMS 14 - 57

A/C clutch relay. To compensate for increased engine
load, the PCM also adjusts idle speed to a scheduled
RPM.
BATTERY VOLTAGEÐPCM INPUT
The powertrain control module (PCM) monitors the
battery voltage input to determine fuel injector pulse
width and generator field control. If battery voltage
is low, the PCM increases injector pulse width to
compensate.
BRAKE SWITCHÐPCM INPUT
When the brake switch activates, the powertrain
control module (PCM) receives an input indicating
that the brakes are being applied. After receiving the
input, the PCM vents the speed control servo. Vent-
ing the servo turns the speed control system off.
ENGINE COOLANT TEMPERATURE SENSORÐPCM
INPUT
The coolant temperature sensor is installed behind
the thermostat housing and ignition coil in the ther-
mostat housing (hot box). The PCM supplies 5 volts
to the coolant temperature sensor. The sensor pro-
vides an input voltage to the PCM (Fig. 3). As cool-
ant temperature varies, the coolant temperature
sensor resistance changes resulting in a different in-
put voltage to the PCM. The PCM demands slightly richer air-fuel mixtures
and higher idle speeds until the engine reaches nor-
mal operating temperature. This sensor is also used for cooling fan control.
CAMSHAFT POSITION SENSORÐPCM INPUT
The camshaft position sensor (distributor pick-up)
supplies engine speed and the injector sync signal to
the powertrain control module (PCM). The sensor is
a Hall Effect device (Fig. 4). A shutter (sometimes referred to as an interrupter)
is attached to the distributor shaft. The shutter con-
tains four blades, one per engine cylinder. A switch plate is mounted to the distributor housing above the
shutter. The switch plate contains the camshaft posi-
tion sensor (distributor pick-up) through which the
shutter blades rotate. As the shutter blades pass
through the pick-up, they interrupt the magnetic
field. The Hall effect device in the pick-up senses the
change in the magnetic field and switches on and off
(which creates pulses), generating the input signal to
the PCM. The PCM calculates engine speed through
the number of pulses generated. One of the shutter blades has a window cut into it.
The window tells the PCM which injector to energize.
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM INPUT
The powertrain control module (PCM) supplies 5
volts to the MAP sensor. The MAP sensor converts
intake manifold pressure into voltage. The PCM
monitors the MAP sensor output voltage. As vacuum
increases, MAP sensor voltage decreases proportion-
ately. Also, as vacuum decreases, MAP sensor volt-
age increases proportionately. During cranking, before the engine starts running,
the PCM determines atmospheric air pressure from
the MAP sensor voltage. While the engine operates,
the PCM determines intake manifold pressure from
the MAP sensor voltage. Based on MAP sensor volt-
age and inputs from other sensors, the PCM adjusts
spark advance and the air/fuel mixture. The MAP sensor mounts on the dash panel inside
the engine compartment (Fig. 5). A vacuum hose con-
nects the sensor to the throttle body.
Fig. 3 Coolant Temperature Sensor
Fig. 4 Camshaft Position Sensor (Distributor Pick-Up)
14 - 58 FUEL SYSTEMS Ä

METHANOL CONCENTRATION SENSORÐPCM
INPUT
The methanol concentration sensor contains a mi-
croprocessor that determines the percentage of gaso-
line and methanol in the fuel system. From the
methanol concentration sensor input, the powertrain
control module (PCM) determines the amount of
methanol in the fuel. The vehicle can operate on a
mixtures up to 85 percent methanol, 15 percent gas-
oline. The PCM supplies 8 volts to the methanol concen-
tration sensor. The methanol concentration sensor
output voltages varies with the percent of methanol
in the fuel system. The sensor output voltage (input
for PCM) ranges from 0.5 volts for pure gasoline to
4.50 volts for 85 percent methanol. For two seconds
at key ON when the operator starts the vehicle, the
sensor calibrates the PCM. During the calibration
period the sensor sends 4.45 volts to the PCM as a
correction factor. The methanol concentration sensor has a built-in
shutdown capability. If the sensor shuts down, the
PCM defaults to the previous learned value (output
voltage based on methanol percentage of fuel). The methanol concentration sensor attaches to a
bracket at the rear of the fuel tank, next to the fuel
filler tube (Fig. 6).
HEATED OXYGEN SENSOR (O2SENSOR)ÐPCM
INPUT
The heated oxygen sensor is located in the exhaust
manifold. The sensor provides an input voltage to the
PCM (Fig. 7). The input tells the PCM the oxygen
content of the exhaust gas. The PCM uses this infor-
mation to fine tune the air-fuel ratio by adjusting in-
jector pulse width. Flexible fuel vehicles operate on mixtures of fuel
that contain up to 85 percent methanol and 15 per-
cent unleaded gasoline. Different percentages of
methanol in the fuel require different air/fuel ratios. The methanol concentration sensor inputs tells the
PCM what percentage of methanol is in the fuel. The
PCM calculates the ideal air/fuel ratio from the
methanol concentration sensor input. The heated ox-
ygen sensor input tells the PCM if it has reached the
desired air/fuel ratio.
The O
2sensor produces voltages from 0 to 1 volt,
depending upon the oxygen content of the exhaust
gas in the exhaust manifold. When a large amount of
oxygen is present (caused by a lean air-fuel mixture),
the sensor produces a low voltage. When there is a
lesser amount present (rich air-fuel mixture) it pro-
duces a higher voltage. By monitoring the oxygen
content and converting it to electrical voltage, the
sensor acts as a rich-lean switch. The oxygen sensor is equipped with a heating ele-
ment that keeps the sensor at proper operating tem-
perature during all operating modes. Maintaining
correct sensor temperature at all times allows the
system to enter into closed loop operation sooner.
Also, it allows the system to remain in closed loop
operation during periods of extended idle.
Fig. 5 Manifold Absolute Pressure (MAP) SensorFig. 6 Methanol Concentration Sensor
Fig. 7 Heated Oxygen Sensor
Ä FUEL SYSTEMS 14 - 59

In Closed Loop operation the PCM monitors the O2
sensor input (along with other inputs) and adjusts
the injector pulse width accordingly. During Open
Loop operation the PCM ignores the O
2sensor input.
In Open Loop, the PCM adjusts injector pulse width
based on a preprogrammed (fixed) oxygen sensor in-
put value and other inputs.
SPEED CONTROLÐPCM INPUT
The speed control system provides four separate
voltages (inputs) to the PCM. The voltages corre-
spond to the On/Off, Set, and Resume. The speed control ON voltage informs the PCM
that the speed control system has been activated.
The speed control SET voltage informs the PCM that
a fixed vehicle speed has been selected. The speed
control RESUME voltage indicates the previous fixed
speed is requested. The speed control OFF voltage
tells the PCM that the speed control system has de-
activated. Refer to Group 8H for further speed con-
trol information.
TRANSAXLE PARK/NEUTRAL SWITCHÐPCM
INPUT
The park/neutral switch is located on the auto-
matic transaxle housing (Fig. 8). Manual transaxles
do not use park/neutral switches. The switch pro-
vides an input to the PCM. The input indicates if the
automatic transaxle is in Park, Neutral, or a drive
gear selection. The input is used to determine idle
speed (varying with gear selection), fuel injector
pulse width, and ignition timing advance. The park
neutral switch is sometimes referred to as the neu-
tral safety switch.
THROTTLE POSITION SENSOR (TPS)ÐPCM INPUT
The Throttle Position Sensor (TPS) is mounted on
the throttle body and connected to the throttle blade
shaft (Fig. 9). The TPS is a variable resistor. The
sensor provides the PCM with an input signal (volt-
age) representing throttle blade position. As the po-
sition of the throttle blade changes, the resistance of
the TPS changes. The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The
PCM receives an input signal voltage from the TPS
varying in an approximate range of from 1 volt at
minimum throttle opening (idle) to 4 volts at wide
open throttle. Along with inputs from other sensors,
the PCM uses the TPS input to determine current
engine operating conditions. The PCM adjusts fuel
injector pulse width and ignition timing based on
these inputs.
VEHICLE SPEED SENSORÐPCM INPUT
The vehicle speed sensor (Fig. 10) is located in the
transaxle extension housing. The sensor input is
used by the PCM to determine vehicle speed and dis-
tance traveled.
The vehicle speed sensor generates 8 pulses per
sensor revolution. These signals, along with a closed
throttle signal from the TPS, determine if a closed
throttle deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
Fig. 8 Park Neutral Switch
Fig. 9 Throttle Position Sensor (TPS) and Idle Air Control Motor
Fig. 10 Vehicle Speed Sensor
14 - 60 FUEL SYSTEMS Ä