Chrysler Town & Country/Voyager, Dodge Caravan, Plymouth Voyager. Manual — part 28

CHECK ENGINE LAMP—ENGINE CONTROLLER
OUTPUT

The engine controller supplies a check engine lamp

on/off signal to the instrument panel through the CCD
Bus. The CCD Bus is a communications port. Various
modules use the CCD Bus to exchange information.

The check engine lamp comes on each time the

ignition key is turned ON and stays on for 3 seconds as
a bulb test. The check engine lamp warns the operator
that the engine controller has entered a Limp-in mode.
During Limp-in Mode, the controller attempts to keep
the system operational. The check engine lamp signals
the need for immediate service. In limp-in mode, the
Engine controller compensates for the failure of certain
components that send incorrect signals. The controller
substitutes for the incorrect signals with inputs from
other sensors.

Signals that can trigger the Check Engine

Lamp.
• Coolant Temperature Sensor

• Manifold Absolute Pressure Sensor

• Throttle Position Sensor

• Battery Voltage Input

• An Emission Related System (California vehicles)

• Charging system

The Check Engine Lamp can also be used to display

fault codes. Cycle the ignition switch on, off, on, off, on,
within five seconds and any fault codes stored in the
Engine controller will be displayed. Refer to On Board
Diagnostics in the General Diagnosis—Multi-Point
Fuel Injection, 3.0L Engine section of this Group for
Fault Code Descriptions.

DIAGNOSTIC CONNECTOR—ENGINE CONTROLLER
OUTPUT

The diagnostic connector provides the technician

with the means to connect the DRB II tester to diag-
nosis the vehicle.

ELECTRONIC AUTOMATIC TRANSMISSION
CONTROLLER—ENGINE CONTROLLER OUTPUT

The Electronic Automatic Transmission Controller

and the Engine Controller supply information to each
other through the CCD Bus. The information includes
engine speed and vehicle load. The engine controller
uses the information when adjusting the fuel and
ignition strategy.

EMISSION MAINTENANCE REMINDER (EMR)
LAMP—ENGINE CONTROLLER OUTPUT

The

Emissions

Maintenance

Reminder

System

(EMR) is incorporated into the engine controller. The
engine controller records the vehicle mileage and
stores it into memory every 8 miles. At that time, the
engine controller checks for the 60,000, 82,500, and
120,000 mileage trip points. When the current mileage
matches one of the above mentioned trip points, the
EMR lamp on the instrument panel is activated.

Certain components must be replaced at the indi-

cated mileage, or when the EMR lamp stays on with
the key in the on position, whichever occurs first. After
performing the required maintenance, the EMR lamp
must be reset to turn the lamp off.

For more information, refer to Group 25 or the

appropriate diagnostic manual.

FUEL INJECTORS—ENGINE CONTROLLER OUTPUT

The fuel injectors are electrical solenoids (Fig. 15).

The injector contains a pintle that closes off an orifice
at the nozzle end. When electric current is supplied to
the injector, the armature and pintle move a short
distance against a spring, allowing fuel to flow out the
orifice. Because the fuel is under high pressure, a fine
spray is developed in the shape of a hollow cone. The
spraying action atomizes the fuel, adding it to the air
entering the combustion chamber.

Fig. 15 Fuel Injector—3.0L Engine

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FUEL SYSTEM

14 - 59

The injectors are positioned in the intake manifold

with the nozzle ends directly above the intake valve
port (Fig. 16).

The fuel injectors are operated by the engine control-

ler. They are energized in a sequential order during all
engine operating conditions except start up. The con-
troller initially energizes all injectors at the same time.
Once the engine controller determines crankshaft po-
sition, it begins energizing the injectors in sequence.

Battery voltage is supplied to the injectors through

the ASD relay. The engine controller provides the
ground path for the injectors. By switching the ground
path on and off, the controller adjusts injector pulse
width. Pulse width is the amount of time the injector is
energized. The controller adjusts injector pulse width
based on inputs it receives.

IGNITION COIL—ENGINE CONTROLLER OUTPUT

The auto shutdown (ASD) relay provides battery

voltage to the ignition coil. The engine controller pro-
vides a ground contact (circuit) for energizing coil.
When the controller breaks the contact, the energy in
the coil primary transfers to the secondary causing the
spark. The engine controller 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 Relay—Engine Controller Output in this section
for relay operation.

The auto shutdown (ASD) relay supplies battery

voltage to the positive terminal of the ignition coil. The
engine controller de-energizes the ASD relay if it does
not receive an input from the distributor pick-up. Refer
to ‘‘Auto Shutdown (ASD) Relay—Engine Controller
Output’’ in this section for relay operation.

The ignition coil is mounted on a bracket next to the

air cleaner (Fig. 17).

PART THROTTLE UNLOCK SOLENOID—ENGINE
CONTROLLER OUTPUT

Three-speed automatic transaxles use a part throttle

unlock solenoid. The engine controller controls the
lock-up of the torque convertor through the part
throttle unlock solenoid. The transmission is locked up
only in direct drive mode. Refer to Group 21 for
transmission information.

RADIATOR FAN RELAY—ENGINE CONTROLLER
OUTPUT

The radiator fan is energized by the engine controller

through the radiator fan relay. The radiator fan relay is
located on the drivers side fender well near to the
engine controller (Fig. 13). The engine controller
grounds the radiator fan relay when engine coolant
reaches a predetermined temperature or when the air
conditioning system is turned on.

SPEED CONTROL SOLENOIDS—ENGINE CONTROL-
LER OUTPUT

The speed control vacuum and vent solenoids are

operated by the engine controller. When the engine
controller supplies a ground to the vacuum solenoid,
the speed control system opens the throttle plate.
When the controller supplies a ground to the vent
solenoid, the throttle blade closes. The engine control-
ler balances the two solenoids to maintain the set
speed. Refer to Group 8H for speed control information.

TACHOMETER—ENGINE CONTROLLER OUTPUT

The engine controller supplies engine RPM to the

instrument panel tachometer through the CCD Bus.
The CCD Bus is a communications port. Various mod-
ules use the CCD Bus to exchange information. Refer
to Group 8E for more information.

MODES OF OPERATION

As input signals to the engine controller change, the

engine controller adjusts its response to the out-

Fig. 16 Fuel Injector Location

Fig. 17 Ignition Coil

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FUEL SYSTEM

.

put devices. For example, the engine controller must
calculate a different injector pulse width and ignition
timing for idle than for wide open throttle (WOT).
There are several different modes of operation that
determine how the engine controller responds to the
various input signals.

There are two different areas of operation, OPEN

LOOP and CLOSED LOOP.

During OPEN LOOP modes the engine controller

receives input signals and responds according to preset
engine controller programming. Input from the oxygen
(O

2

) sensor is not monitored during OPEN LOOP

modes.

During CLOSED LOOP modes the engine controller

does monitor the oxygen (O

2

) sensor input. This input

indicates to the engine controller whether or not the
calculated injector pulse width results in the ideal
air-fuel ratio of 14.7 parts air to 1 part fuel. By
monitoring the exhaust oxygen content through the O

2

sensor, the engine controller can fine tune the injector
pulse width. Fine tuning injector pulse width allows
the engine controller to achieve optimum fuel economy
combined with low emissions.

The 3.0L sequential MPI system 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

The engine start-up (crank), 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 multi-point fuel injection system is acti-

vated by the ignition switch, the following actions
occur:
• The engine controller determines atmospheric air
pressure from the MAP sensor input to determine basic
fuel strategy.
• The engine controller monitors the coolant tempera-
ture sensor and throttle position sensor input. The
engine controller modifies fuel strategy based on these
inputs.

When the key is in the ON position and the engine is

not running (zero rpm), the auto shutdown (ASD) relay
and fuel pump relay are not energized. Therefore
battery voltage is not supplied to the fuel pump,
ignition coil, fuel injectors 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 engine controller receives a distributor signal,

it energizes the auto shutdown (ASD) relay and fuel
pump relay. These relays supply battery voltage to the
fuel pump, fuel injectors, ignition coil, and oxygen
sensor heating element. If the engine controller does
not receive a distributor input, the ASD relay and fuel
pump relay will be de-energized after approximately
one second.

The engine controller energizes all six injectors until

it determines crankshaft position from the distributor
pick-up signals. The controller determines crankshaft
position within 2 engine revolutions.

Once crankshaft position is determined, the control-

ler begins energizing the injectors in sequence. The
controller adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off.

When the engine idles within

664 RPM of its target

RPM, the controller compares current MAP sensor
value with the atmospheric pressure value received
during the Ignition Switch On (zero RPM) mode. If the
controller does not detect a minimum difference be-
tween the two values, it sets a MAP fault into memory.

Once the ASD and fuel pump relays have been

energized, the engine controller:
• determines injector pulse width based on coolant
temperature, manifold absolute pressure (MAP) and
the number of engine revolutions since cranking was
initiated.
• 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 engine controller:
• coolant temperature

• crankshaft position (distributor pick-up)

• manifold absolute pressure (MAP)

• engine speed (distributor pick-up)

• throttle position

• A/C switch

• battery voltage

The controller adjusts injector pulse width and con-

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

The engine controller adjusts engine idle speed by

regulating the automatic idle speed motor and ignition
timing.

.

FUEL SYSTEM

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CRUISE OR IDLE MODE

When the engine is at operating temperature this

is a CLOSED LOOP mode. During cruising speed the
following inputs are received by the engine control-
ler:
• coolant temperature

• crankshaft position (distributor pick-up)

• manifold absolute pressure

• engine speed (distributor pick-up)

• throttle position

• exhaust gas oxygen content

• A/C control positions

• battery voltage

The controller adjusts injector pulse width and con-

trols injector synchronization by turning the individ-
ual ground paths to the injectors On and Off.

The engine controller adjusts engine idle speed and

ignition timing. The engine controller controls the
air/fuel ratio according to the oxygen content in the
exhaust gas.

ACCELERATION MODE

This is a CLOSED LOOP mode. The engine con-

troller recognizes an abrupt increase in throttle posi-
tion or MAP pressure as a demand for increased
engine output and vehicle acceleration. The engine
controller 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 engine
controller:
• coolant temperature

• crankshaft position (distributor pick-up)

• manifold absolute pressure

• engine speed (distributor pick-up)

• throttle position

• exhaust gas oxygen content

• A/C control positions

• battery voltage

The engine controller 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. The engine controller
may reduce injector firing to once per engine revolu-
tion. This helps maintain better control of the air-
fuel mixture (as sensed through the O

2

sensor).

During a deceleration condition, the engine control-

ler grounds the exhaust gas recirculation (EGR) sole-
noid and the evaporative purge solenoid. When the
solenoids are grounded, EGR and canister purge
functions stop.

WIDE OPEN THROTTLE MODE

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

throttle operation, the following inputs are received
by the engine controller:
• coolant temperature

• crankshaft position (distributor pick-up)

• manifold absolute pressure

• engine speed (distributor pick-up)

• throttle position

When the engine controller senses wide open throt-

tle condition through the throttle position sensor
(TPS) it will:
• Provide a ground for the electrical EGR transducer
(EET) solenoid (California vehicles only). When the
controller grounds the solenoid, the EGR system
stops operating.
• De-energize the air conditioning relay. This dis-
ables the air conditioning system.

The exhaust gas oxygen content input is not ac-

cepted by the engine controller during wide open
throttle operation. The engine controller 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:
• All outputs are turned off.

• No inputs are monitored.

• The engine controller shuts down.

THROTTLE BODY

The throttle body assembly (Fig. 18) is located at

the left end of the air intake plenum. The throttle
body houses the throttle position sensor and the au-
tomatic idle speed motor. Air flow through the throt-
tle body is controlled by a cable operated throttle
blade located in the base of the throttle body.

FUEL SUPPLY CIRCUIT

Fuel is supplied to the fuel rail by an electric pump

mounted in the fuel tank. The pump inlet is fitted
with a filter to prevent water and other contami-
nants from entering the fuel supply circuit.

Fuel pressure is controlled to a preset level above

intake manifold pressure by a pressure regulator.
The pressure regulator is mounted on the fuel rail.
The regulator uses intake manifold pressure as a ref-
erence.

FUEL PRESSURE REGULATOR

The pressure regulator is a mechanical device lo-

cated on the fuel rail, downstream of the fuel injec-
tors (Fig. 19). The regulator maintains a constant
328 kPa (47.6 psi) across the fuel injector tip.

The regulator contains a spring loaded rubber dia-

phragm that covers the fuel return port. When the
fuel pump is operating, fuel flows past the injectors

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FUEL SYSTEM

.