2001 DODGE RAM width

DESCRIPTION SPECIFICATION
CYLINDER HEAD AND VALVES
Valve Seat Angle 44.5É
Runout (Max.) 0.0762 mm (0.003 in.)
Width (Finish) ± Intake 1.016 ± 1.524 mm
(0.040 ± 0.060 in.)
Valve Face Angle 45É
Valve Head Diameter
Intake 48.640 ± 48.900 mm
(1.915 ± 1.925 in.)
Exhaust 41.123 ± 41.377 mm
(1.619 ± 1.629 in.)
Overall Length
Intake 145.19 ± 145.82 mm
(5.716 ± 5.741 in.)
Exhaust 145.54 ± 146.18 mm
(5.730 ± 5.755 in.)
Lift (@ zero lash)
Intake 9.91 mm (0.390 in.)
Exhaust 10.34 mm (0.407 in.)
Stem Diameter 7.900 ± 7.920 mm
(0.311 ± 0.312 in.)
Guide Bore 9.500 ± 9.525 mm
(0.374 ± 0.375 on.)
Stem to Guide Clearance 0.025 ± 0.076 mm
(0.001 ± 0..003 in.)
Service Limit 0.4318 (0.017 in.)
Valve Spring Free Length 49.962 mm (1.967 in.)
Spring Tension
Valve Closed 378 N @ 41.66 mm
(85 lbs. @ 1.64 in.)
Valve Open 890 N @ 30.89 mm
(200 lbs. @ 1.212 in.)
Number of Coils 6.8
Installed Height 41.66 mm (1.64 in.)
Wire Diameter 4.50 mm (0.177 in.)DESCRIPTION SPECIFICATION
HYDRAULIC TAPPETS
Body Diameter 22.949 ± 22.962 mm
(0.9035 ± 0.9040 in.)
Clearance (to bore) 0.0203 ± 0.0610 mm
(0.0008 ± 0.0024 in.)
Dry Lash 1.524 ± 5.334 mm
(0.060 ± 0.210 in.)
Push Rod Length 195.52 ± 196.02 mm
(7.698 ± 7.717 in.)
OIL PRESSURE
Curb Idle (Min.*) 83 kPa (12 psi)
@ 3000 rpm 345 ± 414 kPa (50 ± 60
psi)
* If oil pressure is zero at curb idle, DO NOT RUN
ENGINE.
OIL PUMP
Clearance over Rotors
(Max.)0.1906 mm (0.0075 in.)
Cover Out of Flat (Max.) 0.051 mm (0.002 in.)
Inner Rotor Thickness
(Min.)14.925 ± 14.950 mm
(0.5876 ± 0.5886 in.)
Outer Rotor
Clearance (Max.) 0.1626 mm (0.006 in.)
Diameter (Min.) 82.461 mm (3.246 in.)
Thickness (Min.) 14.925 mm (0.5876 in.)
Tip Clearance between
Rotors
(Max.) 0.584 mm (0.0230 in.)
PISTONS
Clearance at Top of Skirt 0.013 ± 0.038 mm
(0.0005 ± 0.0015 in.)
Piston Length 82.5 mm (3.25 in.)
Piston Ring Groove
Depth
#1&2 91.30 ± 91.55 mm
(3.594 ± 3.604 in.)
#3 92.90 ± 93.15 mm
(3.657 ± 3.667 in.)
BR/BEENGINE 8.0L 9 - 185
ENGINE 8.0L (Continued)

REAMER SIZE CHART
REAMER O/S VALVE GUIDE SIZE
0.076 mm 8.026 - 8.052 mm
(0.003 in.) (0.316 - 0.317 in.)
0.381 mm 8.331 - 8.357 mm
(0.015 in.) (0.316 - 0.329 in.)
(5) Slowly turn reamer by hand and clean guide
thoroughly before installing new valve.Ream the
valve guides from standard to 0.381 mm (0.015
inch). Use a 2 step procedure so the valve
guides are reamed true in relation to the valve
seat:
²Step 1ÐReam to 0.0763 mm (0.003 inch).
²Step 2ÐReam to 0.381 mm (0.015 inch).
REFACING VALVES AND VALVE SEATS
The intake and exhaust valves have a 45É face
angle and a 45É to 44 1/2É seat angle (Fig. 17).
VALVE FACE AND SEAT ANGLES CHART
ITEM DESCRIPTION SPECIFICATION
ASEAT WIDTH 1.016 - 1.524
mm
INTAKE (0.040 - 0.060
in.)
SEAT WIDTH 1.016 - 1.524
mm
EXHAUST (0.040 - 0.060
in.)
BFACE ANGLE
(INT. and EXT.) 45É
CSEAT ANGLE
(INT. and EXT.) 44óÉ
DCONTACT
SURFACE Ð
VALVES
Inspect the remaining margin after the valves are
refaced (Fig. 18). Valves with less than 1.190 mm
(0.047 inch) margin should be discarded.
VALVE SEATS
(1) When refacing valve seats, it is important that
the correct size valve guide pilot be used for reseat-
ing stones. A true and complete surface must be
obtained.
(2) Measure the concentricity of valve seat using a
dial indicator. Total runout should not exceed 0.038
mm (0.0015 inch) total indicator reading.
Fig. 16 Measuring Valve Guide Wear
1 - VALVE
2 - SPECIAL TOOL C-3339
Fig. 17 Valve Face and Seat Angles
1 - CONTACT POINT
9 - 196 ENGINE 8.0LBR/BE
INTAKE/EXHAUST VALVES & SEATS (Continued)

(3) Inspect the valve seat with Prussian blue to
determine where the valve contacts the seat. To do
this, coat valve seat LIGHTLY with Prussian blue
then set valve in place. Rotate the valve with light
pressure. If the blue is transferred to the center of
valve face, contact is satisfactory. If the blue is trans-
ferred to the top edge of valve face, lower valve seat
with a 15É stone. If the blue is transferred to bottom
edge of valve face raise valve seat with a 60É stone.
(4) When seat is properly positioned the width of
valve seats should be 1.016-1.524 mm (0.040-0.060
inch).
VALVE SPRING INSPECTION
Whenever valves have been removed for inspection,
reconditioning or replacement, valve springs should
be tested. As an example the compression length of
the spring to be tested is 1-5/16 inch. Turn table of
Universal Valve Spring Tester Tool until surface is in
line with the 1-5/16 inch mark on the threaded stud.
Be sure the zero mark is to the front (Fig. 19). Place
spring over stud on the table and lift compressing
lever to set tone device. Pull on torque wrench until
ping is heard. Take reading on torque wrench at this
instant. Multiply this reading by 2. This will give the
spring load at test length. Fractional measurements
are indicated on the table for finer adjustments.
Refer to specifications to obtain specified height and
allowable tensions. Discard the springs that do not
meet specifications.
REMOVALÐVALVE STEM SEALS
NOTE: This procedure is done with the cylinder
head installed.
(1) Disconnect the negative cable from the battery.
(2) Set engine basic timing to Top Dead Center
(TDC) and remove air cleaner.
(3) Remove cylinder head covers (Refer to 9 -
ENGINE/CYLINDER HEAD/CYLINDER HEAD
COVER(S) - REMOVAL) and spark plugs (Refer to 8
- ELECTRICAL/IGNITION CONTROL/SPARK
PLUG - REMOVAL).
(4) Using suitable socket and flex handle at crank-
shaft retaining bolt, turn engine so that the piston of
the cylinder to be worked on, is at TDC on the com-
pression stroke.
(5) Remove rocker arms (Refer to 9 - ENGINE/
CYLINDER HEAD/ROCKER ARM / ADJUSTER
ASSY - REMOVAL).
(6) With air hose attached to an adapter installed
in the spark plug hole, apply 620-689 kPa (90-100
psi) air pressure.
(7) Using Valve Spring Compressor Tool
MD-998772A with adapter 6716A (Fig. 20), compress
valve spring and remove retainer valve locks and
valve spring.
(8) Remove the valve stem seal.
REMOVALÐVALVES AND VALVE SPRINGS
(1) Remove the cylinder head (Refer to 9 -
ENGINE/CYLINDER HEAD - REMOVAL).
(2) Special studs must be used to adapt the Valve
Spring Compressor Tool to the V-10 cylinder head
(Fig. 21). Install the metric end into the Special Tool
MD998772A and the 5/16 end into the cylinder head.
Fig. 18 Intake and Exhaust Valves
1 - MARGIN
2 - VALVE SPRING RETAINER LOCK GROOVE
3 - STEM
4-FACE
Fig. 19 Testing Valve Spring for Compressed
1 - TORQUE WRENCH
2 - VALVE SPRING TESTER
BR/BEENGINE 8.0L 9 - 197
INTAKE/EXHAUST VALVES & SEATS (Continued)

EXCESSIVE BLUE SMOKE
POSSIBLE CAUSE CORRECTION
Valve seals are worn, brittle, or improperly installed. Replace valve stem oil seals (Refer to 9 - ENGINE/
CYLINDER HEAD/INTAKE/EXHAUST VALVES &
SEATS - REMOVAL).
Valve stems and/or guides are worn. Remove valves and inspect valves and guides. (Refer
to 9 - ENGINE/CYLINDER HEAD/INTAKE/EXHAUST
VALVES & SEATS - STANDARD PROCEDURE).
Broken or Improperly installed piston rings. Tear down engine and inspect piston rings.
Excessive piston ring end gap. Remove pistons and measure piston ring end gap
(Refer to 9 - ENGINE/ENGINE BLOCK/PISTON RINGS
- STANDARD PROCEDURE).
Excessive cylinder bore wear and taper. Remove pistons and measure cylinder bore wear and
taper (Refer to 9 - ENGINE/ENGINE BLOCK -
STANDARD PROCEDURE).
Cylinder damage. Remove pistons and inspect cylinder bore for cracks or
porosity. Repair with cylinder liner if necessary. (Refer
to 9 - ENGINE/ENGINE BLOCK - STANDARD
PROCEDURE).
Piston damage. Remove pistons and inspect for cracks, holes. Measure
piston for out-of-round and taper (Refer to 9 -
ENGINE/ENGINE BLOCK/PISTON & CONNECTING
ROD - INSPECTION).
Turbocharger failure. (Refer to 11 - EXHAUST SYSTEM/TURBOCHARGER
SYSTEM/TURBOCHARGER - INSPECTION).
STANDARD PROCEDUREÐFORM-IN-PLACE
GASKETS & SEALERS
There are numerous places where form-in-place
gaskets are used on the engine. Care must be taken
when applying form-in-place gaskets to assure
obtaining the desired results.Do not use form-in-
place gasket material unless specified.Bead size,
continuity, and location are of great importance. Too
thin a bead can result in leakage while too much can
result in spill-over which can break off and obstruct
fluid feed lines. A continuous bead of the proper
width is essential to obtain a leak-free gasket.
There are numerous types of form-in-place gasket
materials that are used in the engine area. Mopart
Engine RTV GEN II, MopartATF-RTV, and Mopart
Gasket Maker gasket materials, each have different
properties and can not be used in place of the other.
MOPARtENGINE RTV GEN II
MopartEngine RTV GEN II is used to seal com-
ponents exposed to engine oil. This material is a spe-
cially designed black silicone rubber RTV that
retains adhesion and sealing properties when
exposed to engine oil. Moisture in the air causes the
material to cure. This material is available in three
ounce tubes and has a shelf life of one year. After one
year this material will not properly cure. Alwaysinspect the package for the expiration date before
use.
MOPARtATF RTV
MopartATF RTV is a specifically designed black
silicone rubber RTV that retains adhesion and seal-
ing properties to seal components exposed to auto-
matic transmission fluid, engine coolants, and
moisture. This material is available in three ounce
tubes and has a shelf life of one year. After one year
this material will not properly cure. Always inspect
the package for the expiration date before use.
MOPARtGASKET MAKER
MopartGasket Maker is an anaerobic type gasket
material. The material cures in the absence of air
when squeezed between two metallic surfaces. It will
not cure if left in the uncovered tube. The anaerobic
material is for use between two machined surfaces.
Do not use on flexible metal flanges.
MOPARtGASKET SEALANT
MopartGasket Sealant is a slow drying, perma-
nently soft sealer. This material is recommended for
sealing threaded fittings and gaskets against leakage
of oil and coolant. Can be used on threaded and
machined parts under all temperatures. This mate-
rial is used on engines with multi-layer steel (MLS)
cylinder head gaskets. This material also will pre-
BR/BEENGINE 5.9L DIESEL 9 - 237
ENGINE 5.9L DIESEL (Continued)

DESCRIPTION SPECIFICATION
(0.014 ± 0.0177 in.)
Intermediate 0.85 ± 1.15 mm
(0.0334 ± 0.0452 in.)
Oil Control 0.250 ± 0.550 mm
(0.010 ± 0.0215 in.)
Connecting Rods
Pin Bore Diameter (Max.) 40.042 mm (1.5764 in.)
Side Clearance 0.100 ± 0.330 mm
(0.004 ± 0.013 in.)
CYLINDER HEAD
Overall Flatness End to
End (Max.)0.30 mm (0.012 in.)
Overall Flatness Side to
Side (Max.)0.076 mm (0.003 in.)
Intake Valve Seat Angle 30É
Exhaust Valve Seat Angle 45É
Valve Seat Width
(Min.) 1.49 mm (0.059 in.)
(Max.) 1.80 mm (0.071 in.)
Valve Margin (Min.) 0.72 mm (0.031 in.)
OIL PRESSURE
At Idle 69 kPa (10 psi)
At 2,500 rpm 207 kPa (30 psi)
Regulating Valve Opening
Pressure448 kPa (65 psi)
Oil Filter Bypass Pressure
Setting344.75 kPa (50 psi)TORQUE
TORQUE CHART 5.9L DIESEL ENGINE
DESCRIPTION N´m In. Ft.
Lbs. Lbs.
Connecting RodÐBolts
Step 1 35 Ð 26
Step 2 70 Ð 51
Step 3 100 Ð 73
Cylinder HeadÐBolts
Step 1 80 Ð 59
Step 2 105 Ð 77
Step 3 Verify 105 Ð 77
Step 4 Rotate All Bolts 1/4
Turn
Cylinder Head CoverÐBolts 24 18 Ð
Fuel Delivery Lines (High
Pressure)
At Pump 24 Ð 18
At Cylinder Head 38 Ð 28
Fuel Drain LineÐBanjo 24 Ð 18
(rear of head)
Oil PanÐBolts 24 Ð 18
Oil PanÐDrain Plug 60 Ð 44
Oil Pressure RegulatorÐPlug 80 Ð 60
Oil Pressure Sender/Switch 16 Ð 12
Oil PumpÐBolts 24 Ð 18
Oil Suction Tube (Flange)Ð
Bolts24 Ð 18
Oil Suction Tube (Brace)Ð
Bolt24 Ð 18
Rocker Arm/PedestalÐBolts 36 Ð 27
BR/BEENGINE 5.9L DIESEL 9 - 243
ENGINE 5.9L DIESEL (Continued)

(1) Install IAC motor to throttle body.
(2) Install and tighten two mounting bolts (screws)
to 7 N´m (60 in. lbs.) torque.
(3) Install electrical connector.
(4) Install air cleaner assembly.
INSTALLATION - 8.0L
The IAC motor is located on the back of the throt-
tle body (Fig. 33).
(1) Install IAC motor to throttle body.
(2) Install and tighten two mounting bolts (screws)
to 7 N´m (60 in. lbs.) torque.
(3) Install electrical connector.
(4) Install air cleaner housing to throttle body.
(5) Install 4 air cleaner housing mounting nuts.
Tighten nuts to 11 N´m (96 in. lbs.) torque.
(6) Install air cleaner housing cover.
INTAKE AIR TEMPERATURE
SENSOR
DESCRIPTION - 3.9L/5.2L/5.9L/8.0L
The 2±wire Intake Manifold Air Temperature (IAT)
sensor is installed in the intake manifold with the
sensor element extending into the air stream.
The IAT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as intake mani-
fold temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION - 3.9L/5.2L/5.9L/8.0L
The IAT sensor provides an input voltage to the
Powertrain Control Module (PCM) indicating the
density of the air entering the intake manifold based
upon intake manifold temperature. At key-on, a
5±volt power circuit is supplied to the sensor from
the PCM. The sensor is grounded at the PCM
through a low-noise, sensor-return circuit.
The PCM uses this input to calculate the following:
²Injector pulse-width
²Adjustment of spark timing (to help prevent
spark knock with high intake manifold air-charge
temperatures)
The resistance values of the IAT sensor is the same
as for the Engine Coolant Temperature (ECT) sensor.
REMOVAL - 3.9L/5.2L/5.9L
The intake manifold air temperature sensor is
located in the front/side of the intake manifold (Fig.
34).
(1) Remove air cleaner assembly.
(2) Disconnect electrical connector at sensor (Fig.
34).
(3) Remove sensor from intake manifold.
REMOVAL - 8.0L
The intake manifold air temperature sensor is
located in the side of the intake manifold near the
front of throttle body (Fig. 35).
(1) Disconnect electrical connector at sensor.
(2) Remove sensor from intake manifold.
INSTALLATION - 3.9L/5.2L/5.9L
The intake manifold air temperature sensor is
located in the front/side of the intake manifold (Fig.
34).
Fig. 34 Air Temperature SensorÐ3.9L/5.2L/5.9L
1 - INTAKE MANIFOLD AIR TEMPERATURE SENSOR
2 - ELECTRICAL CONNECTOR
Fig. 35 Air Temperature SensorÐ8.0L Engine
1 - INTAKE MANIFOLD AIR TEMP. SENSOR
2 - INTAKE MANIFOLD
BR/BEFUEL INJECTION - GASOLINE 14 - 43
IDLE AIR CONTROL MOTOR (Continued)

(1) Install sensor to intake manifold. Tighten to
12±15 N´m (110±130 in. lbs.) torque.
(2) Install electrical connector.
(3) Install air cleaner.
INSTALLATION - 8.0L
The intake manifold air temperature sensor is
located in the side of the intake manifold near the
front of throttle body (Fig. 35).
(1) Install sensor to intake manifold. Tighten to
12±15 N´m (110±130 in. lbs.) torque.
(2) Install electrical connector.
MANIFOLD ABSOLUTE
PRESSURE SENSOR
DESCRIPTION - 3.9L/5.2L/5.9L/8.0L
On 3.9L/5.2L/5.9L engines, the MAP sensor is
mounted on the side of the engine throttle body. The
sensor is connected to the throttle body with a rubber
L-shaped fitting.
On the 8.0L 10±cylinder engine, the MAP sensor is
mounted into the right side of the intake manifold.
OPERATION - 3.9L/5.2L/5.9L/8.0L
The MAP sensor is used as an input to the Power-
train Control Module (PCM). It contains a silicon
based sensing unit to provide data on the manifold
vacuum that draws the air/fuel mixture into the com-
bustion chamber. The PCM requires this information
to determine injector pulse width and spark advance.
When manifold absolute pressure (MAP) equals
Barometric pressure, the pulse width will be at max-
imum.
A 5 volt reference is supplied from the PCM and
returns a voltage signal to the PCM that reflects
manifold pressure. The zero pressure reading is 0.5V
and full scale is 4.5V. For a pressure swing of 0±15
psi, the voltage changes 4.0V. To operate the sensor,
it is supplied a regulated 4.8 to 5.1 volts. Ground is
provided through the low-noise, sensor return circuit
at the PCM.
The MAP sensor input is the number one contrib-
utor to fuel injector pulse width. The most important
function of the MAP sensor is to determine baromet-
ric pressure. The PCM needs to know if the vehicle is
at sea level or at a higher altitude, because the air
density changes with altitude. It will also help to cor-
rect for varying barometric pressure. Barometric
pressure and altitude have a direct inverse correla-
tion; as altitude goes up, barometric goes down. At
key-on, the PCM powers up and looks at MAP volt-
age, and based upon the voltage it sees, it knows the
current barometric pressure (relative to altitude).
Once the engine starts, the PCM looks at the voltageagain, continuously every 12 milliseconds, and com-
pares the current voltage to what it was at key-on.
The difference between current voltage and what it
was at key-on, is manifold vacuum.
During key-on (engine not running) the sensor
reads (updates) barometric pressure. A normal range
can be obtained by monitoring a known good sensor.
As the altitude increases, the air becomes thinner
(less oxygen). If a vehicle is started and driven to a
very different altitude than where it was at key-on,
the barometric pressure needs to be updated. Any
time the PCM sees Wide Open Throttle (WOT), based
upon Throttle Position Sensor (TPS) angle and RPM,
it will update barometric pressure in the MAP mem-
ory cell. With periodic updates, the PCM can make
its calculations more effectively.
The PCM uses the MAP sensor input to aid in cal-
culating the following:
²Manifold pressure
²Barometric pressure
²Engine load
²Injector pulse-width
²Spark-advance programs
²Shift-point strategies (certain automatic trans-
missions only)
²Idle speed
²Decel fuel shutoff
The MAP sensor signal is provided from a single
piezoresistive element located in the center of a dia-
phragm. The element and diaphragm are both made
of silicone. As manifold pressure changes, the dia-
phragm moves causing the element to deflect, which
stresses the silicone. When silicone is exposed to
stress, its resistance changes. As manifold vacuum
increases, the MAP sensor input voltage decreases
proportionally. The sensor also contains electronics
that condition the signal and provide temperature
compensation.
The PCM recognizes a decrease in manifold pres-
sure by monitoring a decrease in voltage from the
reading stored in the barometric pressure memory
cell. The MAP sensor is a linear sensor; meaning as
pressure changes, voltage changes proportionately.
The range of voltage output from the sensor is usu-
ally between 4.6 volts at sea level to as low as 0.3
volts at 26 in. of Hg. Barometric pressure is the pres-
sure exerted by the atmosphere upon an object. At
sea level on a standard day, no storm, barometric
pressure is approximately 29.92 in Hg. For every 100
feet of altitude, barometric pressure drops .10 in. Hg.
If a storm goes through it can change barometric
pressure from what should be present for that alti-
tude. You should know what the average pressure
and corresponding barometric pressure is for your
area.
14 - 44 FUEL INJECTION - GASOLINEBR/BE
INTAKE AIR TEMPERATURE SENSOR (Continued)

(3) Install MAP sensor mounting bolts (screws).
Tighten screws to 3 N´m (25 in. lbs.) torque.
(4) Install air cleaner.
INSTALLATION - 8.0L
The MAP sensor is mounted into the right upper
side of the intake manifold (Fig. 38). A rubber gasket
is used to seal the sensor to the intake manifold. The
rubber gasket is part of the sensor and is not ser-
viced separately.
(1) Check the condition of the sensor seal. Clean
the sensor and lubricate the rubber gasket with clean
engine oil.
(2) Clean the sensor opening in the intake mani-
fold.
(3) Install the sensor into the intake manifold.
(4) Install sensor mounting bolts. Tighten bolts to
2 N´m (20 in. lbs.) torque.
(5) Install the electrical connector to sensor.
O2 SENSOR
DESCRIPTION
The Oxygen Sensors (O2S) are attached to, and
protrude into the vehicle exhaust system. Depending
on the emission package, the vehicle may use a total
of either 2 or 4 sensors.
3.9L/5.2L/Light Duty 5.9L Engine:Four sensors
are used: 2 upstream (referred to as 1/1 and 2/1) and
2 downstream (referred to as 1/2 and 2/2). With this
emission package, the right upstream sensor (2/1) is
located in the right exhaust downpipe just before the
mini-catalytic convertor. The left upstream sensor
(1/1) is located in the left exhaust downpipe just
before the mini-catalytic convertor. The right down-
stream sensor (2/2) is located in the right exhaust
downpipe just after the mini-catalytic convertor, and
before the main catalytic convertor. The left down-
stream sensor (1/2) is located in the left exhaust
downpipe just after the mini-catalytic convertor, and
before the main catalytic convertor.
Medium and Heavy Duty 8.0L V-10 Engine:
Four sensors are used (2 upstream, 1 pre-catalyst
and 1 post-catalyst). With this emission package, the
1/1 upstream sensor (left side) is located in the left
exhaust downpipe before both the pre-catalyst sensor
(1/2), and the main catalytic convertor. The 2/1
upstream sensor (right side) is located in the right
exhaust downpipe before both the pre-catalyst sensor
(1/2), and the main catalytic convertor. The pre-cata-
lyst sensor (1/2) is located after the 1/1 and 2/1 sen-
sors, and just before the main catalytic convertor.
The post-catalyst sensor (1/3) is located just after the
main catalytic convertor.Heavy Duty 5.9L Engine:Two sensors are used.
They arebothreferred to as upstream sensors (left
side is referred to as 1/1 and right side is referred to
as 2/1). With this emission package, a sensor is
located in each of the exhaust downpipes before the
main catalytic convertor.
OPERATION
An O2 sensor is a galvanic battery that provides
the PCM with a voltage signal (0-1 volt) inversely
proportional to the amount of oxygen in the exhaust.
In other words, if the oxygen content is low, the volt-
age output is high; if the oxygen content is high the
output voltage is low. The PCM uses this information
to adjust injector pulse-width to achieve the
14.7±to±1 air/fuel ratio necessary for proper engine
operation and to control emissions.
The O2 sensor must have a source of oxygen from
outside of the exhaust stream for comparison. Cur-
rent O2 sensors receive their fresh oxygen (outside
air) supply through the wire harness. This is why it
is important to never solder an O2 sensor connector,
or pack the connector with grease.
Four wires (circuits) are used on each O2 sensor: a
12±volt feed circuit for the sensor heating element; a
ground circuit for the heater element; a low-noise
sensor return circuit to the PCM, and an input cir-
cuit from the sensor back to the PCM to detect sen-
sor operation.
Oxygen Sensor Heaters/Heater Relays:
Depending on the emissions package, the heating ele-
ments within the sensors will be supplied voltage
from either the ASD relay, or 2 separate oxygen sen-
sor relays. Refer to 8, Wiring Diagrams to determine
which relays are used.
The O2 sensor uses a Positive Thermal Co-efficient
(PTC) heater element. As temperature increases,
resistance increases. At ambient temperatures
around 70ÉF, the resistance of the heating element is
approximately 4.5 ohms. As the sensor's temperature
increases, resistance in the heater element increases.
This allows the heater to maintain the optimum
operating temperature of approximately 930É-1100ÉF
(500É-600É C). Although the sensors operate the
same, there are physical differences, due to the envi-
ronment that they operate in, that keep them from
being interchangeable.
Maintaining correct sensor temperature at all times
allows the system to enter into closed loop operation
sooner. Also, it allows the system to remain in closed
loop operation during periods of extended idle.
In Closed Loop operation, the PCM monitors cer-
tain O2 sensor input(s) along with other inputs, and
adjusts the injector pulse width accordingly. During
Open Loop operation, the PCM ignores the O2 sensor
input. The PCM adjusts injector pulse width based
14 - 46 FUEL INJECTION - GASOLINEBR/BE
MANIFOLD ABSOLUTE PRESSURE SENSOR (Continued)