Dodge Viper SRT-10 (ZB). Manual - part 199

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
injector pulse width.

OPERATION - MODES OF 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) After the engine is started, the closed loop

timer must count down to zero. The engine coolant
temperature must be over 0F for the closed loop
timer to initiate. The following start up coolant tem-
peratures are used to determine the closed loop timer
start time.

• If the coolant is over -4F the PCM will wait 100

seconds.

• If the coolant is over 14F the PCM will wait 70

seconds.

• If the coolant is over 45F the PCM will wait 45

seconds.

• If the coolant is over 63F the PCM will wait 25

seconds.

(2) For other temperatures the PCM will interpo-

late the correct waiting time.

(3) O2 sensor voltage must stay below ~1.02 Volts.
(4) The engine is NOT in decel fuel shut-off or

WOT mode.

(5) The engine speed is below 3808 RPM.

The multi-port fuel injection systems has the fol-

lowing 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,

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, upstream
O2 sensor heaters, and hydraulic fan module.

ENGINE START-UP MODE

If the clutch pedal is depressed, the starter button

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, (EGR solenoid and PCV
heater if equipped) and heated oxygen sensors.

• 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.

14 - 26

FUEL INJECTION

FUEL INJECTION (Continued)

• After determining crankshaft position, the PCM

begins energizing the injectors in sequence. It adjusts
injector pulse width and controls injector synchroni-
zation by turning the individual ground paths to the
injectors On and Off.

• When the engine idles within ±64 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:

• MAP

• Engine RPM

• Battery voltage

• Engine coolant temperature

• Inlet/Intake air temperature (IAT)

• 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:

• Manifold Absolute Pressure (MAP)

• Crankshaft position (engine speed)

• Engine coolant temperature

• Inlet/Intake air temperature (IAT)

• Camshaft position

• Throttle position

• A/C switch

• Battery voltage

• Vehicle speed

• 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:

• Manifold absolute pressure

• Crankshaft position (engine speed)

• Inlet/Intake air temperature

• Engine coolant temperature

• Camshaft position

• Throttle position

• A/C control inputs

• O2 Sensors

• 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, if 2nd trip with fault.

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

• Purge system monitor

• Catalyst efficiency monitor

• All inputs monitored for proper voltage range,

rationality.

• 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, after 2
trips.

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 or Calculated Battery Tem-

perature

• Engine coolant temperature

• Engine run time

• Inlet/Intake air temperature

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.

DECELERATION MODE

This is a CLOSED LOOP mode. During decelera-

tion the following inputs are received by the PCM:

• A/C control inputs

FUEL INJECTION

14 - 27

FUEL INJECTION (Continued)

• Battery voltage

• Inlet/Intake air temperature

• Engine coolant temperature

• Crankshaft position (engine speed)

• Exhaust gas oxygen content (upstream heated

oxygen 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

• Manifold absolute pressure

• Throttle position
The PCM senses a wide-open-throttle condition

through the Throttle Position Sensor (TPS).

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. When the PCM
goes into closed loop Short Term Correction mode, it
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 33% (+/-) 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
other six are low rpm. Each of these cells is a specific
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.

14 - 28

FUEL INJECTION

FUEL INJECTION (Continued)

Long term adaptive memory can change the pulse-

width by as much as 33%, which means it can correct
for all of short term. It is possible to have a problem

that would drive long term to 33% and short term to
another 33% for a total change of 66% 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

12 Neu-

tral

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.

SPECIFICATIONS

TORQUE

DESCRIPTION

N·m

Ft. Lbs.

In. Lbs.

Accelerator Bracket Bolt

4.0

Accelerator Pedal

105

Air Cleaner Screws

2.3

Coolant Sensor

10.2

Oil Temperature Sensor

10.2

Crankshaft Position Sen-

sor Bolt

Fuel Rail Bolts

105

IAC Motor Bolts

MAP Sensor

Oxygen Sensor

Throttle Body Mounting

Bolts

105

Throttle Position Sensor

Screws

2.1

FUEL INJECTION

14 - 29

FUEL INJECTION (Continued)

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