Chrysler Pacifica. Manual - part 734

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.

• Wide Open Throttle-open loop

DECELERATION MODE

This is a CLOSED LOOP mode. During decelera-

tion the following inputs are received by the PCM:

• A/C status

• 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

• Throttle position sensor

• IAC motor (solenoid) 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 (Open Loop). 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 and disables
EGR (if equipped).

The PCM adjusts injector pulse width to supply a

predetermined amount of additional fuel, based on
MAP and RPM.

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.

FUEL CORRECTION or ADAPTIVE MEMORIES

DESCRIPTION

In Open Loop, the PCM changes pulse width with-

out feedback from the O2 Sensors. Once the engine
warms up to approximately 30 to 35° F, the PCM
goes into closed loop Short Term Correction and
utilizes feedback from the O2 Sensors. Closed loop
Long Term Adaptive Memory is maintained above
170° to 190° F unless the PCM senses wide open
throttle. At that time the PCM returns to Open Loop
operation.

OPERATION

Short Term

The first fuel correction program that begins func-

tioning is the short term fuel correction. This system
corrects fuel delivery in direct proportion to the read-
ings from the Upstream O2 Sensor.

The PCM monitors the air/fuel ratio by using the

input voltage from the O2 Sensor. When the voltage
reaches its preset high or low limit, the PCM begins
to add or remove fuel until the sensor reaches its
switch point. The short term corrections then begin.

The PCM makes a series of quick changes in the

injector pulse-width until the O2 Sensor reaches its
opposite preset limit or switch point. The process
then repeats itself in the opposite direction.

Short term fuel correction will keep increasing or

decreasing

injector

pulse-width

based

upon

the

upstream O2 Sensor input. The maximum range of
authority for short term memory is 25% (+/-) of base
pulse-width. Short term is violated and is lost when
ignition is turned OFF.

Long Term

The second fuel correction program is the long

term adaptive memory. In order to maintain correct
emission throughout all operating ranges of the
engine, a cell structure based on engine rpm and load
(MAP) is used.

Ther number of cells varies upon the driving con-

ditions. Two cells are used only during idle, based
upon TPS and Park/Neutral switch inputs. There
may be two other cells used for deceleration, based
on TPS, engine rpm, and vehicle speed. The other
twelve cells represent a manifold pressure and an
rpm range. Six of the cells are high rpm and the

FUEL INJECTION

14 - 27

FUEL INJECTION (Continued)

other six are low rpm. Each of these cells has a spe-
cific MAP voltage range Typical Adaptive Memory
Fuel Cells.

As the engine enters one of these cells the PCM

looks at the amount of short term correction being
used. Because the goal is to keep short term at 0 (O2
Sensor switching at 0.5 volt), long term will update
in the same direction as short term correction was
moving to bring the short term back to 0. Once short
term is back at 0, this long term correction factor is
stored in memory.

The values stored in long term adaptive memory

are used for all operating conditions, including open

loop and cold starting. However, the updating of the
long term memory occurs after the engine has
exceeded approximately 170°-190° F, with fuel control
in closed loop and two minutes of engine run time.
This is done to prevent any transitional temperature
or start-up compensations from corrupting long term
fuel correction.

Long term adaptive memory can change the pulse-

width by as much as 25%, which means it can correct
for all of short term. It is possible to have a problem
that would drive long term to 25% and short term to
another 25% for a total change of 50% away from
base pulse-width calculation.

TYPICAL ADAPTIVE MEMORY FUEL CELLS

Open

Throttle

Open

Throttle

Open

Throttle

Open

Throttle

Open

Throttle

Open

Throttle

Idle

Decel

Vacuum

Above 1,984

rpm

13 Drive

Below 1,984

rpm

Neutral

MAP volt =

1.4

2.0

2.6

3.3

3.9

Fuel Correction Diagnostics

There are two fuel correction diagnostic routines:
• Fuel System Rich

• Fuel System Lean
A DTC is set and the MIL is illuminated if the

PCM detects either of these conditions. This is deter-
mined based on total fuel correction, short term
times long term.

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

(Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/POWERTRAIN CONTROL MOD-
ULE - DESCRIPTION) .

SPECIFICATIONS

TORQUE

DESCRIPTION

N·m

Ft. Lbs.

In. Lbs.

MAP Sensor

4.5

O2 Sensor

IAC

5.5

Fuel Rail Bolts

250

TPS

5.1

14 - 28

FUEL INJECTION

FUEL INJECTION (Continued)

SPECIAL TOOLS

FUEL

Test Kit, Fuel

Adapters, Fuel Pressure Test—6539 and/or 6631

Spanner Wrench—6856

Fuel Line Adapter 1/4

O2S (OXYGEN SENSOR) REMOVAL/INSTALLER-

C4907

OXYGEN SENSOR TOOL

FUEL INJECTION

14 - 29

FUEL INJECTION (Continued)

ACCELERATOR PEDAL

REMOVAL

(1) The accelerator pedal is connected to the throt-

tle body linkage by the throttle cable. The cable is
protected by a plastic sheathing and is connected to
the throttle body linkage. It is connected to the upper
part of the accelerator pedal arm by a plastic
retainer (clip). This retainer (clip) snaps into the top
of the accelerator pedal arm. It is mounted to the
dash panel with 2 studs and nuts (Fig. 1).

(2) There are 2 cables at the throttle body, one for

speed control and throttle control. Remove the throt-
tle cable from throttle body (Fig. 2).

CAUTION: Be careful not to damage or kink the
cable core wire (within the cable sheathing) while
servicing the accelerator pedal or throttle cable.

(3) Removing throttle cable from throttle body

lever (Fig. 3).

(4) Throttle cable attached to pedal (Fig. 4).

Fig. 1 PEDAL ASSEMBLY

Fig. 2 CABLES AND BRACKET

Fig. 3 CABLE AT THROTTLE BODY

Fig. 4 CABLE ATTACHMENT TO PEDAL

14 - 30

FUEL INJECTION

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