1988 JEEP CHEROKEE sensor
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![JEEP CHEROKEE 1988 Service Repair Manual \
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Application](/manual-img/16/57037/w960_57037-1285.png "JEEP CHEROKEE 1988 Service Repair Manual \
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Application")
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Application Champion No.
2.5L ...................................................... RC-12LYC
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SPARK PLUG SPECIFICATIONS \
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Application Gap: In. (mm) Torque: Ft. Lbs. (N.m\
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2.5L .................. .035 (.89) ................... 7-15 (9-20\
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HIGH TENSION WIRE RESISTANCE
Do not puncture spark plug wires with any type of probe.
Remove spark plug wire and check resistance with an ohmmeter.
ADJUSTMENTS
VALVE ARRANGEMENT
* E-I-I-E-E-I-I-E (Front-to-rear).
VALVE CLEARANCE
All models are equipped with hydraulic lifters, which should
be adjusted to zero lash.
IGNITION COIL WIRE
Remove ignition coil wire from coil and distributor cap.
Check terminals for corrosion and clean if necessary. Check coil wire
resistance. Replace wire if resistance is excessive.
HIGH TENSION WIRE RESISTANCE (OHMS)
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Wire Length (In.) Minimum Maximum\
0-15 ........................ 3000 ........................ 10,000
15-25 ....................... 4000 ........................ 15,000
25-35 ....................... 6000 ........................ 20,000
Over 35 ..................... 8000 ........................ 25,000
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DISTRIBUTOR
All models are equipped with a Renix solid state ignition
module. Renix system uses a TDC sensor mounted near the flywheel. The
distributor consists of a cap and rotor. Its only function is to
distribute high voltage to appropriate spark plug. No adjustments are
required on either system.
Page 1289 of 1378
Fig. 3: TBI Idle Speed Control (ISC) Motor Adjustment
Courtesy of Chrysler Motors.
4) Connect ISC motor connector. Turn ignition off for 10
seconds. ISC motor should fully extend. Restart engine. Engine speed
should momentarily be about 3500 RPM and return to idle speed. Turn
ignition off and disconnect tachometer. Apply sealant to adjustment
screw threads. Install air cleaner.
IDLE SPEED (RPM)
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Application Curb Idle
2.5L TBI (ISC Plunger Extended) ............................... 3500\
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NOTE: Holding plunger inward may create an intermittent trouble
code in ECU memory. To clear ECU memory, turn ignition off
and disconnect negative battery cable for 10 seconds.
THROTTLE POSITION SENSOR (TPS) ADJUSTMENT
NOTE: On some models, it may be necessary to remove throttle body
from intake manifold, to access sensor wiring harness.
Automatic Transmission
1) Locate the square TPS connector. Note connector terminal
identification stamped on the back of the connector. Turn ignition on.
2) Connect voltmeter through back of wiring harness
Page 1290 of 1378
connector. Connect negative voltmeter lead to terminal "D" and
positive voltmeter lead to terminal "A" to check input voltage. DO NOT
disconnect TPS connector.
3) Hold throttle plate closed against idle stop and note
voltage. Input voltage should be approximately 5 volts. Disconnect
voltmeter positive lead and connect to terminal "B" to measure output
voltage.
4) With throttle plate closed, measure the output voltage.
The output voltage should be approximately .2 volts. If output voltage
is not within specification, loosen TPS retaining screws.
5) Partially tighten one retaining screw. Rotate TPS to
obtain correct output voltage. Tighten retaining screws once correct
voltage is obtained.
Manual Transmission
1) Turn ignition on. Connect voltmeter through back of wiring
harness connector. Connect negative voltmeter lead to terminal "B" and
positive voltmeter lead to terminal "C". DO NOT disconnect TPS
connector. See Fig. 4.
2) Rotate and hold throttle plate in wide open position.
Ensure throttle linkage contacts stop. Note voltmeter reading. Voltage
reading should be 5 volts at wide open throttle. Return throttle plate
to closed throttle position. Disconnect voltmeter positive lead from
sensor terminal "C" and connect it to terminal "A".
3) Rotate and hold throttle plate in wide open position.
Ensure throttle linkage contacts stop. Note voltmeter reading. Output
voltage should be 4.6-4.7 volts. If voltage is not as specified,
loosen sensor mounting screw. Loosen upper sensor mounting screw for
small adjustments and lower screw for large adjustments.
4) Adjust sensor. Tighten sensor mounting screws. Remove
voltmeter and return throttle plate to closed position. Replace sensor
if specified output voltage cannot be obtained.
Fig. 4: Adjusting Throttle Position Sensor (Man Trans)
Courtesy of Chrysler Motors.
IDLE MIXTURE ADJUSTMENT
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wires connected to switch). Disconnect distributor vacuum advance hose
and connect hose to vacuum switch. Disconnect wire connector from
knock sensor, located in cylinder head.
3) Using a jumper wire, ground knock sensor wire connector to
engine block. Start engine. With engine at idle speed (solenoid
energized), check timing. Adjust timing to one degree more than
specification (if required). See Emission Control Label.
IGNITION TIMING SPECIFICATIONS (DEGREES BTDC@RPM) - 4.2L
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Application Man. Trans. Auto. Trans.
50 State ............. 9 @ 1600 ............... 9 @ 1600
High Altitude ........ 16 @ 1600 ............. 16 @ 1600
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HOT (SLOW) IDLE RPM
4.0L
1) Apply parking brake and place transmission in Neutral
(Drive for automatic transmissions). Operate engine to normal
operating temperature. Turn ignition off.
2) Ensure all accessories are off. Connect positive
tachometer lead to terminal "D1-1" and negative lead to "D2-7" of
diagnostic connectors. See Fig. 3. Disconnect air stepper motor
connector and TPS wiring connector. See Fig. 4.
Fig. 3: Diagnostic Connector Terminal Identification
Courtesy of Chrysler Motors.
Page 1302 of 1378
or vehicle fails emissions testing.
IDLE MIXTURE (TACHOMETER (LEAN DROP) PROCEDURE)
NOTE: On 4.2L engines, ensure idle speed and timing are set prior
to adjusting the idle mixture. If mixture adjustment time
exceeds 3 minutes, run engine at 2000 RPM in Neutral for one
minute, and resume adjustment. On 4.0L engines, idle mixture
adjustment is not possible.
4.2L
1) Remove carburetor and locate roll pins blocking idle
mixture screws. Drill through throttle body on closed end of roll pin
hole. Drive pins out with punch. Reinstall carburetor. Install
tachometer.
2) Operate engine to normal operating temperature, and adjust
curb idle speed. Place automatic transmission selector in Drive
(Neutral for manual transmissions). Turn mixture screws inward until
RPM drops. Turn screws outward until highest RPM is reached.
3) Turn mixture screws inward to obtain the correct decrease
in RPM. See LEAN DROP (RPM) table. Adjust both screws equally. When
mixture is correctly adjusted, replace roll pin to block adjustment
screws.
NOTE: If final RPM differs more than 30 RPM from specified curb
idle speed, reset curb idle, and repeat mixture adjustment.
LEAN DROP (RPM) TABLE
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Application Man. Trans. Auto. Trans.
4.2L .................... 50 ........................ 50
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THROTTLE POSITION SENSOR (TPS)
NOTE: Adjustment of TPS only applies to the 4.0L models. It may be
necessary to remove throttle body from intake manifold, to
access sensor wiring harness.
Checking & Adjusting - 4.0L (Automatic Transmission)
1) Locate the square TPS connector. Note connector terminal
identification stamped on the back of the connector. Turn ignition on.
2) Connect voltmeter through back of wiring harness
connector. Connect negative voltmeter lead to terminal "D" and
positive voltmeter lead to terminal "A" to check input voltage. DO NOT
disconnect TPS connector.
3) Hold throttle plate closed against idle stop and note
voltage. Input voltage should be approximately 5 volts. Disconnect
voltmeter positive lead and connect to terminal "B" to measure output
voltage.
4) With throttle plate closed, measure the output voltage.
The output voltage should be approximately 4.2 volts. If output
voltage is not within specification, loosen TPS retaining screws.
5) Partially tighten one retaining screw. Rotate TPS to
obtain correct output voltage. Tighten retaining screws once correct
voltage is obtained.
Checking & Adjusting - 4.0L (Manual Transmission)
1) Turn ignition on. Connect voltmeter through back of wiring
harness connector. Connect negative voltmeter lead to terminal
"B" and positive voltmeter lead to terminal "A". DO NOT disconnect TPS
connector.
Page 1303 of 1378
2) Hold throttle plate in the closed throttle position
against idle stop and note input voltage reading. Input voltage should
be approximately 5.0 volts.
3) Disconnect positive lead from terminal "A" and connect to
terminal "C" to check output voltage. Output voltage should be checked
with throttle plates fully closed.
4) Output voltage should be approximately 0.8 volts. If
output voltage is not within specification, loosen TPS bottom
retaining screw and pivot sensor for a large adjustment or top
retaining screw for a fine adjustment.
5) Adjust sensor to obtain correct output voltage. Tighten
retaining screws. Remove voltmeter.
COLD (FAST) IDLE RPM
4.2L
Disconnect and plug EGR valve vacuum hose. With engine
running at normal operating temperature, place fast idle screw on
second step of fast idle cam and against shoulder of high step. Turn
screw to adjust fast idle speed.
FAST IDLE SPEED (RPM) TABLE
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Application Man. Trans. Auto. Trans.
4.2L ................... 1700 ..................... 1700
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AUTOMATIC CHOKE SETTING
Choke coil cover is riveted in place and no adjustment is
necessary or possible.
SERVICING
EMISSION CONTROL
See EMISSIONS section.
SPECIFICATIONS
IGNITION
Distributor
All vehicles use a Motorcraft breakerless solid state
distributor.
PICK-UP COIL RESISTANCE TABLE - OHMS @ 75
F (24C) \
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Application Specification
All Models ....................................... 400-800
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TOTAL SPARK ADVANCE TABLE @ 2000 RPM \
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Application W/ Vac. Advance W/O Vac. Advance
4.0L ................ N/A .......................... N/A
4.2L ............... 30.5
................... 7.5-12.5
Page 1321 of 1378
severe weakness that we will look at later). If an injector has a
fault where it occasionally skips a pulse, the meter registers it and
the reading changes accordingly.
Let's go back to figuring out dwell/duty readings by using
injector on-time specification. This is not generally practical, but
we will cover it for completeness. You NEED to know three things:
* Injector mS on-time specification.
* Engine RPM when specification is valid.
* How many times the injectors fire per crankshaft revolution.
The first two are self-explanatory. The last one may require
some research into whether it is a bank-fire type that injects every
360
of crankshaft rotation, a bank-fire that injects every 720 , or
an SFI that injects every 720 . Many manufacturers do not release this
data so you may have to figure it out yourself with a frequency meter.
Here are the four complete steps to convert millisecond on-
time:
1) Determine the injector pulse width and RPM it was obtained
at. Let's say the specification is for one millisecond of on-time at a
hot idle of 600 RPM.
2) Determine injector firing method for the complete 4 stroke
cycle. Let's say this is a 360
bank-fired, meaning an injector fires
each and every crankshaft revolution.
3) Determine how many times the injector will fire at the
specified engine speed (600 RPM) in a fixed time period. We will use
100 milliseconds because it is easy to use.
Six hundred crankshaft Revolutions Per Minute (RPM) divided
by 60 seconds equals 10 revolutions per second.
Multiplying 10 times .100 yields one; the crankshaft turns
one time in 100 milliseconds. With exactly one crankshaft rotation in
100 milliseconds, we know that the injector fires exactly one time.
4) Determine the ratio of injector on-time vs. off-time in
the fixed time period, then figure duty cycle and/or dwell. The
injector fires one time for a total of one millisecond in any given
100 millisecond period.
One hundred minus one equals 99. We have a 99% duty cycle. If
we wanted to know the dwell (on 6 cylinder scale), multiple 99% times
.6; this equals 59.4
dwell.
Weaknesses of Dwell/Duty Meter
The weaknesses are significant. First, there is no one-to-one
correspondence to actual mS on-time. No manufacturer releases
dwell/duty data, and it is time-consuming to convert the mS on-time
readings. Besides, there can be a large degree of error because the
conversion forces you to assume that the injector(s) are always firing\
at the same rate for the same period of time. This can be a dangerous
assumption.
Second, all level of detail is lost in the averaging process.
This is the primary weakness. You cannot see the details you need to
make a confident diagnosis.
Here is one example. Imagine a vehicle that has a faulty
injector driver that occasionally skips an injector pulse. Every
skipped pulse means that that cylinder does not fire, thus unburned O2
gets pushed into the exhaust and passes the O2 sensor. The O2 sensor
indicates lean, so the computer fattens up the mixture to compensate
for the supposed "lean" condition.
A connected dwell/duty meter would see the fattened pulse
width but would also see the skipped pulses. It would tally both and
likely come back with a reading that indicated the "pulse width" was
within specification because the rich mixture and missing pulses
offset each other.
This situation is not a far-fetched scenario. Some early GM
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Fig. 1: Identifying Tie-Off Symbols
4) If the wires are not drawn all the way to another
component (across several pages), a reference will tell you their
final destination.
5) Again, use the legend on the first page of the wiring
diagram to determine the grid number and letter of the referenced
component. You can then turn directly to it without tracing wires
across several pages.
6) The symbols shown in Fig. 1 are called tie-offs. The first
tie-off shown indicates that the circuit goes to the temperature
sensor, and is also a ground circuit.
7) The second symbol indicates that the circuit goes to a
battery positive parallel circuit. The third symbol leads to a
particular component and the location is also given.
8) The lines shown in Fig. 2 are called options. Which path
or option to take depends on what engine or systems the vehicle has.