ignition CHEVROLET DYNASTY 1993 Manual Online

(5) The variation may need to be adjusted. The
variation is the difference between magnetic north
and true north. To set variation refer the to Varia-
tion Setting Procedure. If the compass portion of the display is not lit or
compass readings are not accurate after calibration.
The vehicle may have too much magnetism for the
compass to be accurate or the compass circuitry is
not working properly. Refer to Variance Procedure,
Demagnetizing Procedure and/or Compass Diagnos-
tics.
VARIANCE PROCEDURE
Variance is the difference between magnetic North
and geographic North. In some areas the difference
between magnetic and geographic North is great
enough to cause the compass to give false readings. If
this occurs, the variance must be set.
VARIANCE SETTING PROCEDURE
To set the variance, depress and hold down both
the Comp/Temp button and the U.S./Metric button.
The display will go off and after 5 seconds the VAR
light will come on. Release both buttons. Using the
zone map (Fig. 3) to find your geographic location,
note the zone which you are in. Press the U.S./Metric button until the zone number appears on the display.
Press the Comp/Temp button to enter your zone
number. Do not attach magnetic devices, such as magnetic
CB antennas to the vehicle roof, as they can cause
the compass to give false readings.
DEMAGNETIZING PROCEDURE
Every vehicle has its own magnetic field. This
magnetic field is created by the various processes a
steel roof goes through when the vehicle is built. A
magnetic field also can be created if the roof is sub-
jected to a magnet, example:
² Magnetic c.b. antenna
² Magnetic tipped screwdriver, etc.
If the roof becomes magnetized use a demagnetiz-
ing tool 6029 to demagnetize the roof. In this demagnetizing procedure you will use the
demagnetizing tool to demagnetize the roof and
mounting screws in the overhead console. It is impor-
tant that you follow the instructions below exactly.
The mounting screws and the mounting brackets
around the compass area are steel, and therefore aid
in the demagnetizing of the roof panel. (1) Be sure the ignition switch is in the OFF posi-
tion before you begin the demagnetize procedure. (2) Open the sun glass compartment to gain access
to the overhead console mounting screws.
Fig. 2 Overhead Console
8C - 22 OVERHEAD CONSOLE Ä

(3) Plug the demagnetizing tool into a standard
110/115 volt AC outlet, keeping the demagnetizing
tool at least 12 inches away from the compass area
when plugging it in. (4) Slowly approach the console mounting screw
with the plastic coated tip of the tool for at least 2
seconds. (5) With the demagnetizing tool still energized,
slowly back it away from the screw until the tip is at
least 12 inches from the screw head. (6) After you have pulled at least 12 inches from
the last screw, remove the demagnetizer tool from in-
side of the vehicle and disconnect it from the electri-
cal outlet. (7) Place an 8 1/2 X 11 inch piece of paper length-
wise on the roof of vehicle directly above compass.
The purpose of the paper is to protect the roof panel
from scratches and define the area to be demagne-
tized. (8) Plug in the demagnetizing tool, keeping it at
least 2 feet away from the compass unit. (9) Slowly approach the center of the roof panel at
the windshield with the demagnetizing tool plugged
in. (10) Contact the roof panel with the tip of the tool
and using slow sweeping motions of 1/2 inch between sweeps. Move the tool approximately 4 inches either
side of the centerline and at least 11 inches back
from the windshield. (11) With the demagnetizing tool still energized,
slowly back away from the roof panel until the tip is
at least 2 feet from the roof before unplugging the
tool. (12) Recalibrate compass.
COMPASS DIAGNOSTICS
To place the unit into the diagnostics mode, turn
the vehicle ignition off. Depress the Comp/Temp but-
ton while turning on the ignition/run switch. The
display will then show DO. There are 3 tests that
can be performed when in the diagnostics mode.
Press the U.S./Metric button to choose test desired.
Refer to Fig. 4 and 5.
Test 1 (d1) determines the magnetic field strength
at the compass. The compass displays compensation
numbers which, correspond to the current magnetic
field strength at the compass. The letter N is dis-
played in the compass portion of the display. While a
number which, corresponds to the magnetic field
strength in the North/South direction is displayed.
The temperature portion of the display or the letter
W is displayed in the compass portion of the display.
A number which, corresponds to the magnetic field
strength in the East/West direction is displayed in
the temperature portion of the display. For proper
compass operation the numbers should be between 1
and 14. A number of 7 or 8 is ideal (no vehicle mag-
netism) while numbers approaching 1 or 14 show
that the vehicle is highly magnetic. If the numbers
show that the vehicle is highly magnetic, perform
the demagnetized procedure in this Group and retest
for magnetism at compass. If the numbers show that
the vehicle is highly magnetic, perform the demagne-
tizing procedure in this section and retest for magne-
tism at compass. The compass is not on the CCD bus,
if not functioning properly, refer to the Overhead
Console and Thermometer diagnosis. Test 2 (d2) checks the electronic circuits of the
compass, temperature, and CCD bus. If the test
passes d2 will be displayed, and if the test fails F2
will be displayed. Refer to AG and AJ Body Diagnos-
tic Procedure Manual for further testing procedures.
Fig. 3 Variance Zone MapFig. 4 Overhead Console Connector
Ä OVERHEAD CONSOLE 8C - 23

IGNITION SYSTEMS
CONTENTS
page page
2.2L TBI, 2.5L TBI, 2.5L MPI AND 3.0L IGNITION SYSTEMSÐDIAGNOSTIC PROCEDURES
..... 11
2.2L TBI, 2.5L TBI, 2.5L MPI AND 3.0L IGNI- TION SYSTEMSÐSERVICE PROCEDURES . 14
2.2L TBI, 2.5L TBI, 2.5L MPI AND 3.0L IGNI- TION SYSTEMSÐSYSTEM OPERATION .... 1
2.2L TURBO III, 3.3L AND 3.8L IGNITION SYSTEMÐDIAGNOSTIC PROCEDURES
.... 35
2.2L TURBO III, 3.3L AND 3.8L IGNITION SYSTEMÐSYSTEM OPERATION ......... 24
2.2L TURBO III, 3.3L AND 3.8L IGNITION SYSTEMSÐSERVICE PROCEDURES ...... 39
IGNITION SWITCH ...................... 45
SPECIFICATIONS ....................... 47
GENERAL INFORMATION
Throughout this group, references are made to par-
ticular vehicles by letter designation. A chart ex-
plaining the designations appears in the Introduction
Section of this manual.
2.2L TBI, 2.5L TBI, 2.5L MPI AND 3.0L IGNITION SYSTEMSÐSYSTEM OPERATION
INDEX
page page
Auto Shutdown (ASD) Relay and Fuel Pump Relay . 8
Coolant Temperature Sensor ................. 7
Distributor Cap ........................... 1
Distributor Pick-UpÐ3.0L Engine .............. 7
Distributor Pick-UpÐPCM Input ............... 6
General Information ........................ 1 Ignition Coil
.............................. 9
Manifold Absolute Pressure (MAP) Sensor ...... 8
Powertrain Control Module (PCM) ............. 6
Rotor .................................. 2
Spark Plug Cables ........................ 2
Spark Plugs ............................. 3
GENERAL INFORMATION
This section describes the ignition systems of the
2.2L TBI, 2.5L TBI, 2.5L MPI (flexible fuel AA-body)
and 3.0L engines. The Fuel Injection sections of Group 14 explain On
Board Diagnostics. Group 0, Lubrication and Maintenance, contains
general maintenance information for ignition related
items. The Owner's Manual also contains mainte-
nance information.
DISTRIBUTOR CAP
Remove the distributor cap and inspect the inside
for flash over, cracking of carbon button, lack of
spring tension on carbon button, cracking of cap, and
burned, worn terminals (Fig. 1). Also check for bro-
ken distributor cap towers. If any of these conditions
are present the distributor cap and/or cables should
be replaced. When replacing the distributor cap, transfer cables
from the original cap to the new cap one at a time.
Ensure each cable is installed into the corresponding tower of the new cap. Fully seat the wires into the
towers. If necessary, refer to the appropriate engine
firing order diagram (Fig. 2 or Fig. 3).
Fig. 1 Distributor Cap Inspection
Ä
IGNITION SYSTEMS 8D - 1

Light scaling of the terminals can be cleaned with
a sharp knife. If the terminals are heavily scaled, re-
place the distributor cap. A cap that is greasy, dirty or has a powder-like
substance on the inside should be cleaned with a so-
lution of warm water and a mild detergent. Scrub
the cap with a soft brush. Thoroughly rinse the cap
and dry it with a clean soft cloth.
ROTOR
Replace the rotor if it is cracked, the tip is exces-
sively burned or heavily scaled (Fig. 4). If the spring
terminal does not have adequate tension, replace the
rotor.
SPARK PLUG CABLES
Spark Plug cables are sometimes referred to as sec-
ondary ignition wires. They transfer electrical cur-
rent from the distributor to individual spark plugs at
each cylinder. 2.2L TBI, 2.5L TBI, 2.5L MPI, Turbo
III and 3.0L engines use resistance type cables. The
cables suppress radio frequency emissions from the
ignition system. Check the spark plug cable connections for good
contact at the coil and distributor cap towers and at
the spark plugs. Terminals should be fully seated.
The nipples and spark plug covers should be in good condition. Nipples should fit tightly on the coil and
distributor cap towers and spark plug cover should fit
tight around spark plug insulators. Loose cable connec-
tions can cause ignition malfunctions by permitting
water to enter the towers, corroding, and increasing
resistance. To maintain proper sealing at the ter-
minal connections, the connections should not
be broken unless testing indicates high resis-
tance, an open circuit or other damage.
CAUTION: Do not pull spark plug cables from dis-
tributor cap of four cylinder engines. The cables must
be released from inside the distributor cap (Fig. 5).
Clean high tension cables with a cloth moistened
with a non-flammable solvent and wipe dry. Check for
brittle or cracked insulation.
Fig. 2 Engine Firing OrderÐ2.2L TBI, 2.5L TBI, 2.5L MPI and Turbo III Engines
Fig. 3 Engine Firing OrderÐ3.0L Engine
Fig. 4 Rotor InspectionÐTypical
Fig. 5 Spark Plug Cable Removal/InstallationÐ2.2L and 2.5L TBI Engines
8D - 2 IGNITION SYSTEMS Ä

When testing secondary cables for punctures and
cracks with an oscilloscope follow the equipment
manufacturers instructions. If an oscilloscope is not available, secondary cables
can be tested as follows:
CAUTION: Do not leave any one spark plug cable
disconnected any longer than necessary during test-
ing. Excessive heat could damage the catalytic con-
verter. Total test time must not exceed ten minutes.
(a) With the engine not running, connect one end
of a test probe to a good ground. Use a probe made of
insulated wire with insulated alligator clips on each
end. (b) With engine running, move test probe along
entire length of all cables (approximately 0 to 1/8
inch gap). If punctures or cracks are present there
will be a noticeable spark jump from the faulty area
to the probe. Check the coil cable the same way.
Replace cracked, leaking or faulty cables.
When replacing cables, install the new high
tension cable and nipple assembly over cap or
coil tower. When entering the terminal into the
tower, push lightly, then pinch the large diam-
eter of nipple to release air trapped between the
nipple and tower. Continue pushing on the cable
and nipple until cables are properly seated in the
cap towers. A snap should be heard as terminal
goes into place. Use the same procedure to install cable in coil tower.
Wipe the spark plug insulator clean before reinstalling
cable and cover. Use the following procedure when removing the high
tension cable from the spark plug. First, remove the
cable from the retaining bracket. Then grasp the ter-
minal as close as possible to the spark plug. Rotate the
cover and pull the cable straight back. Pulling on the
cable itself will damage the conductor and termi-
nal connection. Do not use pliers and do not pull
the cable at an angle. Doing so will damage the
insulation, cable terminal or the spark plug in-
sulator. Wipe spark plug insulator clean before
reinstalling cable and cover. Resistance type cable is identified by the words
Electronic Suppression printed on the cable jacket.
Use an ohmmeter to check resistance type cable for
open circuits, loose terminals or high resistance as
follows: (a) Remove cable from spark plug.
(b) Lift distributor cap from distributor with
cables intact. Do not remove cables from cap. The
cables must be removed from the spark plugs. (c) Connect the ohmmeter between spark plug end
terminal and the corresponding electrode inside the
cap, make sure ohmmeter probes are in good contact.
Resistance should be within tolerance shown in the cable resistance chart. If resistance is
not within tolerance, remove cable at cap tower
and check the cable. If resistance is still not within
tolerance, replace cable assembly. Test all spark
plug cables in same manner.
To test coil to distributor cap high tension cable,
remove distributor cap with the cable intact. Do not
remove cable from the cap. Connect the ohmmeter
between center contact in the cap and remove the ca-
ble at coil tower and check cable resistance. If resis-
tance is not within tolerance, replace the cable.
SPARK PLUGS
Resistor spark plugs are used in all engines and
have resistance values of 6,000 to 20,000 ohms when
checked with at least a 1000 volt tester. Remove the spark plugs and examine them for
burned electrodes and fouled, cracked or broken por-
celain insulators. Keep plugs arranged in the order
in which they were removed from the engine. An iso-
lated plug displaying an abnormal condition indi-
cates that a problem exists in the corresponding
cylinder. Replace spark plugs at the intervals recom-
mended in Group O. Undamaged low milage spark plugs can be cleaned
and reused. Refer to the Spark Plug Condition sec-
tion of this group. After cleaning, file the center elec-
trode flat with a small point file or jewelers file.
Adjust the gap between the electrodes (Fig. 6) to the
dimensions specified in the chart at the end of this
section. Always tighten spark plugs to the specified torque.
Over tightening can cause distortion and change
spark plug gap. Tighten spark plugs to 28 N Im (20 ft.
lbs.) torque.
SPARK PLUG CONDITION
NORMAL OPERATING CONDITIONS
The few deposits present will be probably light tan
or slightly gray in color with most grades of commer-
cial gasoline (Fig. 7). There will not be evidence of
electrode burning. Gap growth will not average more
than approximately 0.025 mm (.001 in) per 1600 km
(1000 miles) of operation. Spark plugs that have nor-
mal wear can usually be cleaned, have the electrodes
filed and regapped, and then reinstalled. Some fuel refiners in several areas of the United
States have introduced a manganese additive (MMT)
CABLE RESISTANCE CHART
Ä IGNITION SYSTEMS 8D - 3

for unleaded fuel. During combustion, fuel with
MMT coats the entire tip of the spark plug with a
rust color deposit. The rust color deposits could be
misdiagnosed as being caused by coolant in the com-
bustion chamber. MMT deposits do not affect spark
plug performance.
COLD FOULING (CARBON FOULING)
Cold fouling is sometimes referred to as carbon
fouling. The deposits that cause cold fouling are ba-
sically carbon (Fig. 7). A dry, black deposit on one or
two plugs in a set may be caused by sticking valves
or defective spark plug cables. Cold (carbon) fouling
of the entire set may be caused by a clogged air
cleaner. Cold fouling is normal after short operating periods.
The spark plugs do not reach a high enough operating
temperature during short operating periods.
WET FOULING
A spark plug that is coated with excessive wet fuel or
oil is wet fouled. In older engines, wet fouling can be
caused by worn rings or excessive cylinder wear.
Break-in fouling of new engines may occur be-
fore normal oil control is achieved. In new or
recently overhauled engines, wet fouled spark
plugs can be usually be cleaned and reinstalled.
OIL OR ASH ENCRUSTED
If one or more plugs are oil or oil ash encrusted,
engine oil is entering the combustion chambers (Fig. 8).
Evaluate the engine to determine the cause.
HIGH SPEED MISS When replacing spark plugs because of a high speed
miss condition; wide open throttle operation
should be avoided for approximately 80 km (50
miles) after installation of new plugs. This will
allow deposit shifting in the combustion chamber to
take place gradually and avoid plug destroying splash
fouling shortly after the plug change.
ELECTRODE GAP BRIDGING
Loose deposits in the combustion chamber can cause
electrode gap bridging. The deposits accumulate on the
spark plugs during continuous stop-and-go driving.
When the engine is suddenly subjected to a high torque
load, the deposits partially liquefy and bridge the gap
between the electrodes
Fig. 6 Setting Spark Plug Electrode GapÐTypical
Fig. 7 Normal Operation and Cold (Carbon) FoulingFig. 8 Oil or Ash Encrusted
8D - 4 IGNITION SYSTEMS Ä

(Fig. 9). This short circuits the electrodes. Spark
plugs with electrode gap bridging can be cleaned us-
ing standard procedures.
SCAVENGER DEPOSITS Fuel scavenger deposits may be either white or yel-
low (Fig. 10). They may appear to be harmful, but
are a normal condition caused by chemical additives
in certain fuels. These additives are designed to
change the chemical nature of deposits and decrease
spark plug misfire tendencies. Accumulation on the
ground electrode and shell area may be heavy but
the deposits are easily removed. Spark plugs with
scavenger deposits can be considered normal in con-
dition and be cleaned using standard procedures.
CHIPPED ELECTRODE INSULATOR A chipped electrode insulator usually results from
bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions,
severe detonation also can separate the insulator
from the center electrode (Fig. 11). Replace spark
plugs with chipped electrode insulators. PREIGNITION DAMAGE
Excessive combustion chamber temperature can
cause preignition damage. The center electrode dis-
solves first and the ground electrode dissolves some-
what later (Fig. 12). Insulators appear relatively
deposit free. Determine if the spark plug has the cor-
rect heat range rating for the engine, if ignition tim-
ing is over advanced or if other operating conditions
are causing engine overheating. The heat range rat-
ing refers to the operating temperature of a particu-
lar type spark plug. Spark plugs are designed to
operate within specific temperature ranges depend-
ing upon the thickness and length of the center elec-
trode and porcelain insulator.
SPARK PLUG OVERHEATING Overheating is indicated by a white or gray center
electrode insulator that also appears blistered (Fig.
13). The increase in electrode gap will be consider-
ably in excess of 0.001 in per 1000 miles of operation.
This suggests that a plug with a cooler heat range
rating should be used. Over advanced ignition tim-
Fig. 9 Electrode Gap Bridging
Fig. 10 Scavenger Deposits
Fig. 11 Chipped Electrode Insulator
Fig. 12 Preignition Damage
Ä IGNITION SYSTEMS 8D - 5

ing, detonation and cooling system malfunctions also
can cause spark plug overheating.
SPARK PLUG SERVICE
When replacing the spark plug and coil cables,
route the cables correctly and secure them in the ap-
propriate retainers. Failure to route the cables prop-
erly can cause the radio to reproduce ignition noise,
cross ignition of the spark plugs or short circuit the
cables to ground.
SPARK PLUG REMOVAL
Always remove the spark plug cable by grasping at
the spark plug boot turning, the boot 1/2 turn and
pulling straight back in a steady motion. (1) Prior to removing the spark plug spray com-
pressed air around the spark plug hole and the area
around the spark plug. (2) Remove the spark plug using a quality socket
with a rubber or foam insert. (3) Inspect the spark plug condition. Refer to
Spark Plug Condition in this section.
SPARK PLUG GAP ADJUSTMENT Check the spark plug gap with a gap gauge. If the
gap is not correct, adjust it by bending the ground
electrode (Fig. 6).
SPARK PLUG INSTALLATION (1) To avoid cross threading, start the spark plug
into the cylinder head by hand. (2) Tighten spark plugs to 28 N Im (20 ft. lbs.)
torque. (3) Install spark plug cables over spark plugs.
POWERTRAIN CONTROL MODULE (PCM)
The ignition system is regulated by the powertrain
control module (PCM) (Fig. 14). The PCM supplies
battery voltage to the ignition coil through the Auto
Shutdown (ASD) Relay. The PCM also controls the
ground circuit for the ignition coil. By switching the ground path for the coil on and off, the PCM adjusts
ignition timing to meet changing engine operating
conditions.
During the crank-start period the PCM advances
ignition timing a set amount. During engine opera-
tion, the amount of spark advance provided by the
PCM is determined by these input factors:
² coolant temperature
² engine RPM
² available manifold vacuum
The PCM also regulates the fuel injection system.
Refer to the Fuel Injection sections of Group 14.
DISTRIBUTOR PICK-UPÐPCM INPUT
The engine speed input is supplied to the power-
train control module (PCM) by the distributor pick-
up. The distributor pick-up is a Hall Effect device
(Fig. 15 or Fig. 16).
A shutter (sometimes referred to as an interrupter)
is attached to the distributor shaft. The shutter con-
tains four blades, one per engine cylinder. A switch
plate is mounted to the distributor housing above the
shutter. The switch plate contains the distributor
Fig. 14 Powertrain control module (PCM)
Fig. 15 DistributorÐ2.2L and 2.5L TBI Engines
Fig. 13 Spark Plug Overheating
8D - 6 IGNITION SYSTEMS Ä

pick-up (a Hall Effect device and magnet) through
which the shutter blades rotate. As the shutter
blades pass through the pick-up, they interrupt the
magnetic field. The Hall effect device in the pick-up
senses the change in the magnetic field and switches
on and off (which creates pulses), generating the in-
put signal to the PCM. The PCM calculates engine
speed through the number of pulses generated. On 2.5L MPI (flexible fuel AA-Body) engines, one
of the shutter blades has a window cut into it. The
PCM determines injector synchronization from the
window. Also, the PCM uses the input for detonation
control.
DISTRIBUTOR PICK-UPÐ3.0L ENGINE
The distributor pick-up provides two inputs to the
powertrain control module (PCM). From one input
the PCM determines RPM (engine speed). From the
other input it derives crankshaft position. The PCM
regulates injector synchronization and adjusts igni-
tion timing and engine speed based on these inputs. The distributor pick-up contains two signal gener-
ators. The pick-up unit consists of 2 light emitting
diodes (LED), 2 photo diodes, and a separate timing
disk. The timing disk contains two sets of slots. Each
set of slots rotates between a light emitting diode
and a photo diode (Fig. 17). The inner set contains 6
large slots, one for each cylinder. The outer set con-
tains several smaller slots. The outer set of slots on the rotating disk repre-
sents 2 degrees of crankshaft rotation. Up to 1200
engine RPM, the PCM uses the input from the outer
set of slots to increase ignition timing accuracy. The outer set of slots contains a 10 degree flat spot.
This area is not slotted (Fig. 17). The flat spot tells
the PCM that the next piston at TDC will be number
6. Each piston's position is referenced by one of the
six inner slots (Fig. 18). As each slot on the timing disk passes between the
diodes, they interrupt the beam from the light emit-
ting diode. This creates an alternating voltage in
each photo diode which is converted into on-off
pulses. The pulses are the input to the PCM. During cranking, the PCM cannot determine which
cylinder will be at TDC until the 10 degree flat spot
on the outer set of slots rotates through the optical
unit. Once the flat spot is detected, the PCM knows
piston number 6 will be the next piston at TDC. Since the disk rotates at half crankshaft speed, it
may take up to 2 engine revolutions during cranking
before the PCM determines the position of piston
number 6. For this reason the PCM energizes all six
injectors at the same time until it senses the position
of piston number 6.
COOLANT TEMPERATURE SENSOR
On 2.2L TBI, 2.5L TBI and 2.5L MPI engines, the
coolant temperature sensor is installed behind the
thermostat housing and ignition coil in the hot box
(Fig. 19). On 3.0L engines the sensor is located next
Fig. 16 DistributorÐ2.5L MPI (Flexible Fuel AA-Body)Fig. 17 Distributor Pick-upÐ3.0L Engine
Fig. 18 Inner and Outer Slots of Rotating DiskÐ3.0L Engine
Ä IGNITION SYSTEMS 8D - 7

to the thermostat housing (Fig. 20). The sensor pro-
vides an input voltage to the powertrain control mod-
ule (PCM). The sensor is a variable resistance
(thermistor) with a range of -40ÉF to 265ÉF. As cool-
ant temperature varies, the sensors resistance
changes, resulting in a different input voltage to the
PCM. The PCM contains different spark advance sched-
ules for cold and warm engine operation. The sched-
ules reduce engine emissions and improve
driveability. Because spark advance changes at dif-
ferent engine operating temperatures during warm-
up, all spark advance testing should be done with the
engine fully warmed. The PCM demands slightly richer air-fuel mixtures
and higher idle speeds until the engine reaches nor-
mal operating temperature. The coolant sensor input is also used for radiator
fan control.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor reacts to absolute pressure in the
intake manifold and provides an input voltage to the
powertrain control module (PCM). As engine load
changes, manifold pressure varies. The changes in
engine load causes the MAP sensors output voltage
to change. The change in MAP sensor output voltage
results in a different input voltage to the PCM. The input voltage level supplies the PCM with in-
formation relating to ambient barometric pressure
during engine start-up (cranking) and engine load
while its operating. The PCM uses this input along
with inputs from other sensors to adjust air-fuel mix-
ture. On 2.2L TBI, 2.5L TBI and 2.5L MPI (flexible fuel
AA-body) engines, the MAP sensor is mounted to the
dash panel (Fig. 21 or Fig. 22). On 3.0L engines, the
sensor is mounted to a bracket across from the dis-
tributor (Fig. 23). The sensor is connected to the
throttle body or intake manifold with a vacuum hose
and to the PCM electrically.
AUTO SHUTDOWN (ASD) RELAY AND FUEL PUMP
RELAY
The powertrain control module (PCM) operates the
auto shutdown (ASD) relay and fuel pump relay
through one ground path. The PCM operates the re-
lays by switching the ground path on and off. Both
relays turn on and off at the same time. The ASD relay connects battery voltage to the fuel
injector and ignition coil. The fuel pump relay con-
nects battery voltage to the fuel pump and oxygen
sensor heating element. The PCM turns the ground path off when the igni-
tion switch is in the Off position. Both relays are off.
When the ignition switch is in the On or Crank po-
sition, the PCM monitors the distributor pick-up sig-
Fig. 19 Coolant Temperature SensorÐ2.2L TBI, 2.5L TBI and 2.5L MPI Engines
Fig. 20 Coolant Temperature SensorÐ3.0L Engines
Fig. 21 MAP SensorÐ2.2L and 2.5L TBI Engines
8D - 8 IGNITION SYSTEMS Ä