Chrysler Stratus Convertible. Manual - part 26

Multi-Port Electronic Fuel Injection system. The MPI
system is computer regulated and provides precise
air/fuel ratios for all driving conditions. The Power-
train Control Module (PCM) operates the fuel injec-
tion system.

The PCM regulates:
• Ignition timing

• Air/fuel ratio

• Emission control devices

• Cooling fan

• Charging system

• Idle speed

• Vehicle speed control

Various sensors provide the inputs necessary for

the PCM to correctly operate these systems. In addi-
tion to the sensors, various switches also provide
inputs to the PCM.

The PCM can adapt its programming to meet

changing operating conditions.

Fuel is injected into the intake port above the

intake valve in precise metered amounts through
electrically operated injectors. The PCM fires the
injectors in a specific sequence. Under most operat-
ing conditions, the PCM maintains an air fuel ratio
of 14.7 parts air to 1 part fuel by constantly adjust-
ing injector pulse width. Injector pulse width is the
length of time the injector is open.

The PCM adjusts injector pulse width by opening

and closing the ground path to the injector. Engine
RPM (speed) and manifold absolute pressure (air
density) are the primary inputs that determine injec-
tor pulse width.

FUEL SYSTEM

14 - 21

PCM REPLACEMENT

DESCRIPTION

USE THE DRB SCAN TOOL TO REPROGRAM

THE NEW PCM WITH THE VEHICLES ORIGI-
NAL IDENTIFICATION NUMBER (VIN) AND
THE VEHICLES ORIGINAL MILEAGE. IF THIS
STEP IS NOT DONE A DIAGNOSTIC TROUBLE
CODE (DTC) MAY BE SET.

MODES OF OPERATION

OPERATION

As input signals to the PCM change, the PCM

adjusts its response to 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 differ-
ent 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
programming. Inputs from the upstream and down-
stream heated oxygen sensors are not monitored dur-
ing OPEN LOOP modes, except for heated oxygen
sensor diagnostics (they are checked for shorted con-
ditions at all times).

During CLOSED LOOP modes the PCM monitors

the inputs from the upstream and downstream
heated oxygen sensors. The upstream heated oxygen
sensor input tells the PCM if the calculated injector
pulse width resulted in the ideal air-fuel ratio of 14.7
to one. By monitoring the exhaust oxygen content
through the upstream heated oxygen sensor, the
PCM can fine tune injector pulse width. Fine tuning
injector pulse width allows the PCM to achieve opti-
mum fuel economy combined with low emissions.

For the PCM to enter CLOSED LOOP operation,

the following must occur:

(1) Engine coolant temperature must be over 35°F.
• If the coolant is over 35° the PCM will wait 44

seconds.

• If the coolant is over 50°F the PCM will wait 38

seconds.

• If the coolant is over 167°F the PCM will wait

11 seconds.

(2) For other temperatures the PCM will interpo-

late the correct waiting time.

(3) O2 sensor must read either greater than 0.745

volts or less than 0.1 volt.

(4) The multi-port fuel injection systems has the

following modes of operation:

• Ignition switch ON (Zero RPM)

• Engine start-up

• Engine warm-up

• Cruise

• Idle

• Acceleration

• Deceleration

• Wide Open Throttle

• Ignition switch OFF
(5) The engine start-up (crank), engine warm-up,

deceleration with fuel shutoff and wide open throttle
modes are OPEN LOOP modes. Under most operat-
ing conditions, the acceleration, deceleration (with
A/C on), idle and cruise modes, with the engine at
operating temperature are CLOSED LOOP modes.

IGNITION SWITCH ON (ZERO RPM) MODE

When the ignition switch activates the fuel injec-

tion system, the following actions occur:

• The PCM monitors the engine coolant tempera-

ture sensor and throttle position sensor input. The
PCM determines basic fuel injector pulse width from
this input.

• The PCM determines atmospheric air pressure

from the MAP sensor input to modify injector pulse
width.

When the key is in the ON position and the engine

is not running (zero rpm), the Auto Shutdown (ASD)
and fuel pump relays de-energize after approximately
1 second. Therefore, battery voltage is not supplied to
the fuel pump, ignition coil, fuel injectors and heated
oxygen sensors.

ENGINE START-UP MODE

This is an OPEN LOOP mode. If the vehicle is in

park or neutral (automatic transaxles) or the clutch
pedal is depressed (manual transaxles) the ignition
switch energizes the starter relay. The following
actions occur when the starter motor is engaged.

• If the PCM receives the camshaft position sensor

and crankshaft position sensor signals, it energizes
the Auto Shutdown (ASD) relay and fuel pump relay.
If the PCM does not receive both signals within
approximately one second, it will not energize the
ASD relay and fuel pump relay. The ASD and fuel
pump relays supply battery voltage to the fuel pump,
fuel injectors, ignition coil and heated oxygen sen-
sors.

• The PCM energizes the injectors (on the 69°

degree falling edge) for a calculated pulse width until
it determines crankshaft position from the camshaft
position sensor and crankshaft position sensor sig-
nals. The PCM determines crankshaft position within
1 engine revolution.

• After determining crankshaft position, the PCM

begins energizing the injectors in sequence. It adjusts
injector pulse width and controls injector synchroni-

14 - 22

FUEL SYSTEM

DESCRIPTION AND OPERATION (Continued)

zation by turning the individual ground paths to the
injectors On and Off.

• When the engine idles within 664 RPM of its

target RPM, the PCM compares current MAP sensor
value with the atmospheric pressure value received
during the Ignition Switch On (zero RPM) mode.

Once the ASD and fuel pump relays have been

energized, the PCM determines injector pulse width
based on the following:

• Battery voltage

• Engine coolant temperature

• Engine RPM

• Inlet/Intake air temperature (IAT)

• MAP

• Throttle position

• The number of engine revolutions since cranking

was initiated

During Start-up the PCM maintains ignition tim-

ing at 9° BTDC.

ENGINE WARM-UP MODE

This is an OPEN LOOP mode. The following inputs

are received by the PCM:

• Engine coolant temperature

• Manifold Absolute Pressure (MAP)

• Inlet/Intake air temperature (IAT)

• Crankshaft position (engine speed)

• Camshaft position

• Knock sensor

• Throttle position

• A/C switch

• Battery voltage

• Power steering pressure switch

• Vehicle speed

• Speed control

• O2 sensors
The PCM adjusts injector pulse width and controls

injector synchronization by turning the individual
ground paths to the injectors On and Off.

The PCM adjusts ignition timing and engine idle

speed. Engine idle speed is adjusted 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 or idle
the following inputs are received by the PCM:

• Inlet/Intake air temperature

• Engine coolant temperature

• Manifold absolute pressure

• Crankshaft position (engine speed)

• Camshaft position

• Knock sensor

• Throttle position

• Exhaust gas oxygen content

• A/C control positions

• Power steering pressure switch

• Battery voltage

• Vehicle speed
The PCM adjusts injector pulse width and controls

injector synchronization by turning the individual
ground paths to the injectors On and Off.

The PCM adjusts engine idle speed and ignition

timing. The PCM adjusts the air/fuel ratio according
to the oxygen content in the exhaust gas (measured
by the upstream and downstream heated oxygen sen-
sor).

The PCM monitors for engine misfire. During

active misfire and depending on the severity, the
PCM either continuously illuminates or flashes the
malfunction indicator lamp (Check Engine light on
instrument panel). Also, the PCM stores an engine
misfire DTC in memory.

The PCM performs several diagnostic routines.

They include:

• Oxygen sensor monitor

• Downstream heated oxygen sensor diagnostics

during open loop operation (except for shorted)

• Fuel system monitor

• EGR monitor

• Purge system monitor

• All inputs monitored for proper voltage range.

• All monitored components (refer to the Emission

section for On-Board Diagnostics).

The PCM compares the upstream and downstream

heated oxygen sensor inputs to measure catalytic
convertor efficiency. If the catalyst efficiency drops
below the minimum acceptable percentage, the PCM
stores a diagnostic trouble code in memory.

During certain idle conditions, the PCM may enter

a variable idle speed strategy. During variable idle
speed strategy the PCM adjusts engine speed based
on the following inputs.

• A/C sense

• Battery voltage

• Battery temperature

• Engine coolant temperature

• Engine run time

• Inlet/Intake air temperature

• Power steering pressure switch

• Vehicle mileage

ACCELERATION MODE

This is a CLOSED LOOP mode. The PCM recog-

nizes an abrupt increase in Throttle Position sensor
output voltage or MAP sensor output voltage as a
demand for increased engine output and vehicle
acceleration. The PCM increases injector pulse width
in response to increased fuel demand.

FUEL SYSTEM

14 - 23

DESCRIPTION AND OPERATION (Continued)

DECELERATION MODE

This is a CLOSED LOOP mode. During decelera-

tion the following inputs are received by the PCM:

• A/C sense

• Battery voltage

• Inlet/Intake air temperature

• Engine coolant temperature

• Crankshaft position (engine speed)

• Exhaust gas oxygen content (upstream heated

oxygen sensor)

• Knock sensor

• Manifold absolute pressure

• Power steering pressure switch

• Throttle position

• IAC motor control changes in response to MAP

sensor feedback

The PCM may receive a closed throttle input from

the Throttle Position Sensor (TPS) when it senses an
abrupt decrease in manifold pressure. This indicates
a hard deceleration. In response, the PCM may
momentarily

turn

off

the

injectors.

This

helps

improve fuel economy, emissions and engine braking.

WIDE-OPEN-THROTTLE MODE

This is an OPEN LOOP mode. During wide-open-

throttle operation, the following inputs are used by
the PCM:

• Inlet/Intake air temperature

• Engine coolant temperature

• Engine speed

• Knock sensor

• Manifold absolute pressure

• Throttle position
When the PCM senses a wide-open-throttle condi-

tion through the Throttle Position Sensor (TPS) it de-
energizes the A/C compressor clutch relay. This
disables the air conditioning system.

The PCM does not monitor the heated oxygen sen-

sor inputs during wide-open-throttle operation except
for downstream heated oxygen sensor and both
shorted diagnostics. The PCM adjusts injector pulse
width to supply a predetermined amount of addi-
tional fuel.

IGNITION SWITCH OFF MODE

When the operator turns the ignition switch to the

OFF position, the following occurs:

• All outputs are turned off, unless 02 Heater

Monitor test is being run. Refer to the Emission sec-
tion for On-Board Diagnostics.

• No inputs are monitored except for the heated

oxygen sensors. The PCM monitors the heating ele-
ments in the oxygen sensors and then shuts down.

SYSTEM DIAGNOSIS

OPERATION

The PCM can test many of its own input and out-

put circuits. If the PCM senses a fault in a major
system, the PCM stores a Diagnostic Trouble Code
(DTC) in memory.

For DTC information see On-Board Diagnostics.

CCD BUS

DESCRIPTION

Various controllers and modules exchange informa-

tion through a two-wire communication port called
the CCD Bus.The PCM transmits various monitored
input information and control requests to other mod-
ules on the CCD Bus. The PCM also receives infor-
mation and requests that effects the control of its
outputs from other controllers over the CCD Bus.
The CCD Bus has a measurable voltage of approxi-
mately 2.5 volts.

OPERATION

Various modules exchange information through a

communications port called the CCD Bus. The Pow-
ertrain Control Module (PCM) transmits the Mal-
function Indicator Lamp (Check Engine) On/Off
signal and engine RPM on the CCD Bus. The PCM
receives the Air Conditioning select input, transaxle
gear position input and speed control engage inputs
over the CCD Bus. The PCM also receives the air
conditioning evaporator temperature signal from the
CCD Bus.

The following components access or send informa-

tion on the CCD Bus.

• Instrument Panel

• Body Control Module

• Air Bag System Diagnostic Module

• Full ATC Display Head

• ABS Module

• Transmission Control Module

• Powertrain Control Module

• Travel Module (if equipped)

POWERTRAIN CONTROL MODULE

DESCRIPTION

The Powertrain Control Module (PCM) is a digital

computer containing a microprocessor.

OPERATION

The PCM receives input signals from various

switches and sensors that are referred to as PCM
Inputs. Based on these inputs, the PCM adjusts var-
ious engine and vehicle operations through devices
that are referred to as PCM Outputs.

14 - 24

FUEL SYSTEM

DESCRIPTION AND OPERATION (Continued)

Content .. 24 25 26 27 ..