width DODGE RAM 1999 Service User Guide (1691 Pages)

Loose ................... B ... Require repair or replacement
of affected component.
Lug nut installed
backward ............... B .. Require repair or replacement.
Lug nut mating type
incorrect .............. B ..... Require replacement of nut.
Lug nut mating surface
dished ................. A ..... Require replacement of nut.
Lug nut rounded ......... A . (2) Require replacement of nut.
Lug nut seized .......... A . ( 2) Require replacement of nut.
Stud incorrect .......... B .... Require replacement of stud.
Threads damaged ......... A ... Require repair or replacement
of component with damaged
threads.
Threads stripped ........ A .......... Require replacement of
component with stripped
threads.
( 1) - Some manufacturers require replacement of all studs on
that wheel if two or more studs or nuts on the same
wheel are broken or missing.
( 2) - Only required if removing wheel.
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WHEELS (RIMS)
WARNING: Mounting a regular tire on a high-pressure compact spare
wheel is not permitted. Attempting to mount a tire of one
diameter on a wheel of a different diameter or flange
type may result in serious injury or death. If the wheel
identification stamp is not legible, or cannot be found,
do not use the wheel until the size and type have been
properly identified. Wheels of different diameter,
offset, or width cannot be mixed on the same axle. Bead
seat tapers cannot be interchanged.
WHEEL (RIM) INSPECTION
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Condition Code Procedure
Bead leaking, caused
by wheel ............... A ........... ( 1) Require repair or
replacement.
Bent hub mounting
surface ................ A ............ Require replacement.
Bent rim, causing
vibration .............. 2 ........ ( 1) Suggest replacement.
Broken .................. A ............ Require replacement.
Cast wheel porous,
causing a leak ......... A .. Require repair or replacement.
Clip-on balance weight is
incorrect type
for rim flange ......... 2 ............ Suggest replacement.
Corrosion, affecting
structural integrity ... A ............ Require replacement.
Corrosion build-up on
wheel mounting
surface ................ A ................. Require repair.
Cracked ................. A ............ Require replacement.
Directional/asymmetrical
wheels mounted
incorrectly ............ B ....... Require remounting and/or
repositioning.

E - T H EO RY/O PER ATIO N - R W D - G ASO LIN E

1999 D odge P ic ku p R 1500
1999 ENGINE PERFORMANCE
CHRY - Theory & Operation - Trucks & RWD Vans - Gasoline
Dakota, Durango, Ram Pickup, Ram Van, Ram Wagon
INTRODUCTION
This article covers the basic description and operation of
engine performance related systems and components. Read this article
before working on unfamiliar systems.
COMPUTERIZED ENGINE CONTROLS
POWERTRAIN CONTROL MODULE (PCM)
The PCM is a digital computer that controls ignition timing,
air/fuel ratio, fuel injector pulse width, ignition coil(s), spark
advance, emission control devices, cooling fan, charging system, idle
speed, cruise control (if equipped), fuel pump and tachometer. For PCM\
location, see PCM LOCATION. PCM uses data from various input sources
to control output devices in order to achieve optimum engine
performance for all operating conditions.
PCM has voltage converters that convert battery voltage to
regulated 5-volt output. The 5-volt output powers battery temperature
sensor, Camshaft Position (CMP) sensor on models equipped with
Distributorless Ignition System (DIS) or distributor on models without\
DIS, Crankshaft Position (CKP) sensor, Engine Coolant Temperature
(ECT) sensor, Intake Air Temperature (IAT) sensor, logic circuits,
Manifold Absolute Pressure (MAP) sensor, Throttle Position (TP) sens\
or
and Vehicle Speed Sensor (VSS) on some models.
PCM LOCATION
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Application Location
Dakota & Durango ................. Right Front Fender, Near Firewall
Ram Pickup, Ram Van & Ram Wagon .... On Firewall, Near Wiper Motor
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NOTE: Components are grouped into 2 categories. The first category,
INPUT DEVICES, includes components that control or produce
voltage signals monitored by the PCM. The second category,
OUTPUT SIGNALS, includes components controlled by the PCM
(this is accomplished by the PCM grounding individual
circuits).
INPUT DEVICES
Vehicles are equipped with different combinations of input
devices. Not all devices are used on all models. To determine
component location and input usage on a specific model, see
appropriate wiring diagram in WIRING DIAGRAMS article. Available input
signals include:
A/C Switch
Switch signals PCM that A/C has been selected. PCM then
activates A/C compressor clutch relay and maintains idle speed at a
preprogrammed RPM. This is done through control of Idle Air Control

(IAC) motor.
Battery Temperature Sensor
PCM uses sensor to determine battery temperature and to
control battery charging rate. Temperature data along with battery
voltage data, is used by PCM to vary charging rate. System voltage is
higher at colder temperatures and is gradually reduced at warmer
temperatures.
Battery Voltage
PCM monitors battery voltage to determine fuel injector pulse
width and generator field control. This is done to compensate for
reduced current flow through injector caused by lowered voltage.
Brake Switch
This switch may also be referred to as a brakelight switch.
PCM uses this switch input to maintain idle speed at a preprogrammed
RPM when brakes are applied. If PCM receives an input signal from
brake switch when speed control system is on, PCM will turn speed
control system off.
Camshaft Position (CMP) Sensor
On models equipped with a distributor, CMP sensor is made up
of a Hall Effect switch (sync signal generator) and a rotating pulse
ring (shutter) on distributor shaft. See Fig. 1. On Distributorless
Ignition System (DIS), CMP sensor reads slots in cam timing sprocket.
PCM uses this information along with information from Crankshaft
Position (CKP) sensor to determine if fuel injectors and ignition
coils are properly sequenced for correct cylinders.
Fig. 1: Cut-Away View Of Hall Effect Distributor (Typical)
Courtesy of Chrysler Corp.
Crankshaft Position (CKP) Sensor
CKP sensor detects sets of slots on flywheel/torque converter

drive plate. PCM uses this information to determine fuel injection
sequence, ignition signal and spark timing.
Cruise Control Switch
Cruise control switch provides PCM with 3 separate inputs.
ON/OFF switch input informs PCM that cruise control system has been
activated. SET/COAST switch input informs PCM that set vehicle speed
has been selected, or if depressed will decelerate until switch is
released. RESUME/ACCEL switch input informs PCM that a previously set
speed has been selected or, if depressed, will increase speed until
released. PCM uses these inputs to control cruise control servo.
Engine Coolant Temperature (ECT) Sensor
ECT sensor monitors engine coolant temperature. PCM uses ECT
sensor information to adjust air/fuel mixture and idle speed and to
control radiator cooling fans as necessary.
Fuel Level Sensor
PCM supplies a 5-volt reference signal to fuel module in gas
tank. Fuel level sensor sends a signal to PCM indicating fuel level.
PCM monitors this signal to prevent a false misfire signal if fuel
level is less than 15 percent. PCM also sends this signal to fuel
gauge.
Heated Oxygen Sensor (HO2S)
HO2S produces a small electrical voltage (0-1 volt) when
exposed to heated exhaust gas. HO2S is electrically heated for faster
warm-up. Heating element is powered through Auto Shutdown (ASD) relay.\
HO2S acts like a rich/lean (air/fuel ratio) switch by
monitoring oxygen content in exhaust gas. This information is used by
PCM to adjust air/fuel ratio by adjusting injector pulse width.
HO2S produces low voltage when oxygen content in exhaust gas
is high. When oxygen content in exhaust gas is low, HO2S produces a
higher voltage.
Ignition Switch
Ignition switch sends signal to PCM indicating whether switch
is on, off or cranking (ST). When PCM receives ON signal, it energizes\
ASD relay coil and supplies power to sensors and actuators. When PCM
receives ST signal, it controls fuel injection rate, idle speed,
ignition timing, etc. for optimum cranking conditions.
Intake Air Temperature (IAT) Sensor
IAT sensor measures temperature of incoming intake air. This
information is used by PCM to adjust air/fuel mixture.
Manifold Absolute Pressure (MAP) Sensor
MAP sensor monitors intake manifold vacuum. Sensor transmits
information on manifold vacuum and barometric pressure to PCM. MAP
sensor information is used with information from other sensors to
adjust air/fuel mixture.
Oil Pressure Sensor
Sensor sends a signal to PCM to indicate oil pressure.
Park/Neutral (P/N) Switch (A/T Models)
This switch may also be referred to as a Park/Neutral
Position (PNP) switch. P/N switch is available on vehicles equipped
with A/T only. Switch prevents engine starter from engaging if vehicle
is in any gear except Park or Neutral.
P/N switch input (varied with gear selection) is used to
determine idle speed, fuel injector pulse and ignition timing.

Power Steering Pressure Switch
On 2.5L Dakota only, power steering pressure switch sends a
signal to PCM. PCM will raise idle speed to prevent stalling during
high power steering pressure (375-575 psi), low RPM conditions.
Serial Communication Interface (SCI) Receive
SCI receive circuit is a serial communication link used when
diagnosing vehicle using scan tool. PCM receives data and device
activation commands from scan tool on this circuit.
Throttle Position (TP) Sensor
TP sensor monitors opening angle of throttle blade. TP sensor
will vary output voltage from about .26 volt at minimum throttle
opening (idle), to about 4.5 volts at Wide Open Throttle (WOT). PCM
uses this information and other sensor inputs to determine engine
operation. In response, PCM will adjust fuel injection pulse width and
ignition timing.
Transmission Governor Pressure Sensor (A/T Models)
Sensor sends PCM a signal indicating governor pressure. PCM
uses signal as feedback for governor solenoid control.
Transmission Overdrive/Override (OD/OR) Switch (A/T Models)
On models with Overdrive (OD), PCM regulates 3-4 OD upshift
and downshift through OD solenoid. Transmission OD/OR switch is
mounted in instrument panel.
OD/OR switch is normally closed. If OD/OR switch is depressed
and it opens, transmission will not enter OD. Transmission will
downshift if it is in OD and OD/OR switch is depressed.
OD/OR switch circuit includes a transmission fluid
temperature sensor. If this sensor opens, transmission will not shift
into overdrive, or will downshift if already in overdrive.
Transmission Temperature Sensor (A/T Models)
Transmission temperature sensor monitors transmission fluid
temperature and sends an input signal to PCM. Input signal is used for
controlling torque converter clutch operation, overdrive shifts, low
temperature shift compensation, wide open throttle shift strategy and
governor pressure. Transmission temperature sensor is located in
transmission valve body, incorporated into governor pressure sensor.
If transmission fluid temperature is more than 260
F (126C),
PCM forces a 4-3 downshift and engages torque converter clutch until
fluid cools. Once fluid cools to less than 230
F (110C), PCM allows a
3-4 shift. PCM prevents torque converter clutch engagement and
overdrive operation when fluid temperature is less than 50
F (10C).
Vehicle Speed Sensor (VSS)
VSS generates 8 pulses per sensor revolution. VSS input is
used by PCM to determine vehicle speed and distance traveled, and to
maintain set speed during cruise control operation.
PCM interprets speed sensor input along with TP sensor closed
throttle input. This enables PCM to determine if a closed throttle
deceleration or normal throttle idle (vehicle stopped) condition
exists. During deceleration, PCM controls IAC motor to maintain a
desired MAP value. During idle (vehicle stopped), PCM controls IAC
motor to maintain a desired idle speed.
OUTPUT SIGNALS
NOTE: Each vehicle may be equipped with different combinations of
computer-controlled components. The following components may
NOT be used on all models. To determine component location
and output usage on a specific model, see appropriate wiring

Fuel pump is a positive displacement, immersible pump with a
permanent magnet electric motor. Fuel is drawn in through a separate
filter/strainer at bottom of fuel pump and pushed through filter to
fuel outlet line (to fuel injectors). Voltage to operate pump is
supplied from fuel pump relay. On some models, fuel pump relay is
activated by ASD relay.
Fuel pump module includes a combination fuel filter/fuel
pressure regulator, fuel pump reservoir, a separate in-tank fuel
filter, pressure relief/rollover valve, fuel gauge sending unit and
fuel supply line. See Fig. 3.
Fig. 3: Identifying Fuel Pump Module Components (Typical)
Courtesy of Chrysler Corp.
FUEL CONTROL
Fuel Injectors
Fuel injectors are electric solenoid valves controlled by
PCM. PCM determines when and length of time (pulse width) injectors
should operate by switching ground path on and off. During start-up,
battery voltage is supplied to injectors through ASD relay. On some
models, battery voltage is supplied by charging system once engine is

operating. When ground is supplied to injector by PCM, armature and
pintle inside injector move a short distance against spring and open a
small orifice. Since fuel is under high pressure, a fine spray is
developed.
Modes Of Operation
As input signals to PCM change, PCM adjusts its response to
output devices. Modes of operation come in 2 types, open loop and
closed loop. In open loop mode, PCM is not using input from HO2S and
is responding to preset programming to determine injector pulse width
and ignition timing. In closed loop mode, PCM adjusts ignition timing
and uses input from HO2S to fine tune injector pulse width.
The following inputs may be used to determine PCM mode:
* A/C Control Positions
* A/C Switch
* Battery Voltage
* Brake Switch
* Camshaft Position (CMP) Sensor
* Crankshaft Position (CKP) Sensor
* Engine Coolant Temperature (ECT) Sensor
* Engine Speed (RPM)
* Heated Oxygen Sensor (HO2S)
* Intake Air Temperature (IAT) Sensor
* Manifold Absolute Pressure (MAP) Sensor
* Park/Neutral (P/N) Switch
* Starter Relay
* Throttle Position (TP) Sensor
* Vehicle Speed Sensor (VSS)
From these inputs, PCM determines which mode vehicle is in
and responds appropriately. Not all inputs are used in all modes or by
all models. Modes of operation are:
* Ignition Switch On (Engine Not Running) - This is an open
loop mode. PCM pre-positions IAC motor based on ECT sensor
input. PCM determines atmospheric pressure from MAP sensor
and determines basic fuel strategy. PCM modifies fuel
strategy according to IAT sensor, ECT sensor and TP sensor
inputs. PCM activates ASD relay, which in turn activates fuel
pump for only 2 seconds unless engine is cranked. PCM also
energizes HO2S heater element for approximately 2 seconds
unless engine is cranked.
* Engine Start-Up - This is an open loop mode. When starter is
engaged, PCM receives input from battery voltage, ignition
switch, CKP sensor, CMP sensor, ECT sensor, IAT sensor, MAP
sensor and TP sensor. Based on these inputs, voltage is
applied to fuel injectors with PCM controlling injection
sequence, rate, and pulse width. PCM provides ground for
injectors to fire in proper order.
PCM determines proper ignition timing according to input
received from CKP sensor. If PCM does not receive CKP sensor signal
within 3 seconds after engine begins cranking, fuel injection system
is shut down and a Diagnostic Trouble Code (FTC) is set in PCM memory.\
* Engine Warm-Up - This is an open loop mode. PCM determines
injector pulse width using input information from battery
voltage, CKP sensor, CMP sensor, ECT sensor, IAT sensor, MAP
sensor and TP sensor. PCM also monitors A/C request and P/N
switch (A/T only) for fuel calculation. PCM controls engine
idle speed through IAC motor. PCM controls ignition timing
based on CKP sensor input.

PCM also operates A/C compressor clutch (if A/C is requested)\
through A/C clutch relay. When engine reaches operating temperature,
vehicle will go into idle mode and PCM will begin monitoring HO2S
input and go into closed loop operation.
* Idle - When engine is at operating temperature, this is a
closed loop mode. In idle mode, PCM now adds HO2S signal to
array of inputs used in ENGINE WARM-UP mode. PCM maintains
correct air/fuel ratio by adjusting injector pulse width and
ignition timing. PCM also controls A/C clutch operation (if
A/C is requested).
* Cruise - When engine is at operating temperature, this is a
closed loop mode. Using information from A/C switch, battery
voltage, CKP sensor, ECT sensor, IAT sensor, MAP sensor and
CMP sensor. PCM also monitors A/C request and P/N switch (A/T
only), TP sensor and VSS signals for fuel calculation. PCM
monitors HO2S and adjusts air/fuel ratio as needed. PCM
controls engine idle speed through IAC motor. PCM controls
spark advance as necessary.
* Acceleration - This is an open loop mode. When PCM
recognizes an abrupt increase in throttle position or
manifold pressure as a demand for increased engine output, it
increases injector pulse width in response to increased fuel
demand. HO2S signals are ignored.
* Deceleration - This is an open loop mode when engine is at
operating temperature and under deceleration. When PCM
receives inputs signaling a closed throttle and an abrupt
decrease in manifold pressure, it reduces injector pulse
width to lean air/fuel mixture. Under certain RPM and closed
throttle position conditions, HO2S signals are ignored and
PCM cuts off fuel injection until idle speed is reached. PCM
also drives IAC motor for smooth transition to idle mode.
* Wide Open Throttle - This is an open loop mode. When PCM
senses wide open throttle, it grounds fuel injectors in
sequence, it ignores HO2S input and it controls pulse width
to supply a pre-determined amount of additional fuel. PCM
also adjusts spark advance and disengages A/C clutch for
approximately 15 seconds.
* Ignition Switch Off - This is an open loop mode. PCM drives
IAC motor into position in anticipation of next start-up. All
outputs are turned off, no inputs are monitored and PCM shuts
down.
Sequential Fuel Injection (SFI)
Individual, electrically pulsed injectors (one per cylinder)
are located in intake manifold runners. These injectors are next to
intake valves in intake manifold. PCM controls injection timing based
on crankshaft position signal input. PCM regulates air/fuel mixture by
length of time injector stays open (pulse width) based on inputs from
HO2S, ECT sensor, MAP and other sensors.
IDLE SPEED
NOTE: DO NOT attempt to correct a high idle speed condition by
turning factory sealed throttle body throttle plate set
screw. This will not change idle speed of warm engine, but
may cause cold start problems due to restricted airflow.
Idle Air Control (IAC) Motor
IAC motor adjusts idle speed to compensate for engine load
and ambient temperature by adjusting amount of air flowing through by-
pass in back of throttle body. PCM uses ECT sensor, VSS, TP sensor and

various switch input operations to adjust IAC motor to obtain optimum
idle conditions. Deceleration stall is prevented by increasing airflow
when throttle is closed suddenly.
IGNITION SYSTEM
NOTE: Pickup equipped with 8.0L engine uses Distributorless
Ignition system (DIS). All other models use a Hall Effect
ignition system.
The PCM completely controls ignition system. During
crank/start mode, PCM will set a fixed amount of spark advance for an
efficient engine start. Amount of spark advance or retard is
determined by inputs that PCM receives from ECT sensor, engine vacuum
and engine RPM. During engine operation, PCM can supply an infinite
number of advance curves to ensure proper engine operation.
DISTRIBUTORLESS IGNITION SYSTEM (DIS)
DIS eliminates mechanical ignition components that can wear
out. PCM has complete ignition control and uses a coil pack, CMP
sensor and CKP sensor to control ignition timing. CMP sensor reads
slots in cam timing sprocket. PCM uses this information along with
information from CKP sensor to determine if fuel injectors and
ignition coils are properly sequenced for correct cylinders.
Basic timing is determined by CKP sensor position and is not
adjustable. One complete engine revolution may be required for PCM to
determine crankshaft position during cranking.
Molded ignition coils are used. Each coil fires 2 paired
spark plugs at the same time. One cylinder is on compression stroke
and other cylinder is on exhaust stroke.
HALL EFFECT IGNITION SYSTEM
This system is equipped with a Hall Effect distributor. See
Fig. 1 . Shutter(s) attached to distributor shaft rotate through
distributor Hall Effect switch, also referred to as a CMP sensor,
which contains a distributor pick-up (a Hall Effect device and
magnet). As shutter blade(s) pass through pick-up, magnetic field is
interrupted and voltage is toggled between high and low. PCM uses this
cylinder position data from CMP sensor, along with engine speed (RPM)
and CKP sensor data, to control ignition timing and injector pulse
width to maintain optimum driveability.
EMISSION SYSTEMS
Vehicles are equipped with different combinations of emission
system components. Not all components are used on all models. To
determine component usage on a specific model, see EMISSION
APPLICATIONS - TRUCKS article.
AIR INJECTION SYSTEM
This system adds a controlled amount of air to exhaust gases,
through air relief valve and check valves, to assist oxidation of
hydrocarbons and carbon monoxide in exhaust stream. Air is injected at
catalytic converters.
CRANKCASE VENTILATION (CCV) SYSTEM
CCV system performs same function as a conventional Positive

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