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need help with driveabilty problem

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my buddies XJ will fire up and idle poorly and when fuel is applied it stumbles


we have swapped parts with my mj



knock sensor

air sensor

water sensor



any other ides


we also adjusted the tps

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How about a new fuel filter and some good injector cleaner... like maybe a healthy shot of SEAFOAM?

Check the plugs, cap and rotor as well!! ;)





Remember...always go for the simple stuff first as that is usually the problem. ;)

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Did it ever run properly? If not, don't discount the possibility that some previous "technician" may have had the distributor out, and reinstalled it a tooth or more out of position.


Also, be sure the catalytic converter isn't clogged.

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map sensor is new


injectors are new


fuel filter new



we pulled the dist and made shure every this is tdc



i work for a jeep dealor


i asked one of our tecks


he mentioned the egr valve was stuck in the open position

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fuel filter new

we pulled the dist and made shure every this is tdc he mentioned the egr valve was stuck in the open position


MAYBE that is a problem on mine as well, runs 90% better now than when I first got it BUT.....

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map sensor is new


injectors are new


fuel filter new



we pulled the dist and made shure every this is tdc



i work for a jeep dealor


i asked one of our tecks


he mentioned the egr valve was stuck in the open position

The MAP sensor is in the manifold, the control is on the firewall. Did you change both? A new sensor does not mean the signal is being translated correctly to the ECM.

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this is still a problem


we have


checked fuel pressure


31 lbs if i rember right


replaced fuel rail


pulled and reinstalled distributor


replaced cap




all injectors


2 sets of used 1 compleet set of new


5 coials 4 used 1 new all work fine in outher rigs


we are stumped


working on the truck 3 ase tec's 2 morpar tech,s 1 toyota tech 1 mopar parts rep

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First perhaps mention year and drivetrain.


Ever consider the CPS?






The Powertrain Control Module (PCM) is a dual microprocessor

that receives various signals from engine sensors and provides the

necessary signals to control engine sub-systems. The PCM has a voltage

converter that converts battery voltage to regulated 5-volt or 8-volt

outputs. The regulated 5-volt output is used to power Manifold

Absolute Pressure (MAP) sensor, Throttle Position Sensor (TPS) and

logic circuits. The regulated 8-volt output is used to power

crankshaft position sensor and camshaft position sensor in


The ignition and fuel injection systems are controlled by

the PCM. Based on present engine operating conditions, the PCM is

programmed to provide a precise amount of fuel and the correct

ignition timing to meet existing engine speed and load requirements.

The PCM adjusts ignition timing based on inputs it receives

from camshaft position sensor, MAP sensor, coolant temperature sensor,

throttle position sensor, vehicle speed sensor, transmission gear

selection (automatic transmissions only) and brake switch.

The PCM adjusts idle speed based on inputs it receives from

throttle position sensor, vehicle speed sensor, transmission gear

selection (automatic transmissions only), A/C clutch switch and brake


The PCM also controls the speed (cruise) control system and

alternator charge rate by controlling the alternator field.

NOTE: Components are grouped into 2 categories. The first category

covers INPUT DEVICES, which control or produce voltage

signals that are monitored by the PCM. The second category

covers OUTPUT SIGNALS, which are components controlled by

the PCM.


Vehicles are equipped with different combinations of input

devices. Not all devices are used on all models. To determine the

input device usage on a specific model, see appropriate wiring diagram

in L - WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. The

available input signals include the following:

A/C Pressure Switch & Evaporator Switch

When A/C switch is in ON position and A/C low pressure switch

and evaporator switch are closed, an A/C select signal is sent to PCM.

If A/C low pressure switch or evaporator switch opens, the PCM will

not receive an A/C select signal.

When A/C function is selected (A/C switch on), the A/C

request signal provides information to the PCM from the A/C

temperature control thermostat (evaporator switch). This signal

indicates evaporator temperature is in the proper range for A/C


The A/C request signal is used by PCM to determine required

Idle Air Control (IAC) motor position and to activate or deactivate

A/C compressor clutch. When PCM receives an A/C request signal, it

repositions the IAC motor to increase idle speed. The increased idle

speed compensates for additional engine load caused by engagement of

A/C compressor.

On 4.0L, whenever A/C compressor clutch is energized, PCM

also energizes the radiator (cooling) fan relay. This occurs

regardless on engine coolant temperature.

Alternator Output

The PCM keeps charging system voltage at 13.5-14.8 volts.

Charging system voltage will be adjusted by PCM based on battery

temperature sensor, located within PCM housing. The voltage determined

by PCM as final goal for charging system is called "control" voltage.

The control voltage will be used to determine alternator field control

and to detect if charging system is operating properly.

If sensed voltage is lower than "control" voltage, PCM will

alter duty cycle and ground alternator (rotor) field for a longer

period of time and create a higher alternator output which should

raise sensed voltage level. If sensed voltage is higher than "control"

voltage, PCM will alter duty cycle and lower alternator output which

should lower sensed voltage level.

Battery Voltage Signal

The PCM uses battery voltage level to regulate alternator

field (rotor) duty cycle and alter fuel injector pulse width according

to available voltage. If battery voltage drops, PCM will increase

injector on time to compensate for the reduced fuel flow of injector

caused by the lower voltage. This will permit injector to deliver

proper amount of fuel to the engine.

Brake Switch

The brake switch is mounted on steering column support

bracket, under instrument panel. The PCM uses the brake switch to

determine when brakes are applied. When brakes are applied (brake

switch on) and if PCM sees a TPS opening and a lower speed sensor

rate, it recognizes a deceleration condition and opens up the Idle Air

Control (IAC) motor. The brake switch signal will also disengage speed

(cruise) control operation, if it was engaged.

Coolant Temperature Sensor

The coolant temperature sensor is mounted on top of engine,

next to thermostat housing. It provides an analog signal to the PCM

that is used to calculate injector pulse width and ignition timing

when engine is cold. Input from the coolant temperature sensor will

also affect Idle Air Control (IAC) motor position and spark advance


Crankshaft Position Sensor

The Hall Effect type crankshaft position sensor is mounted on

transaxle bellhousing. The sensor reads slots (4 per cylinder) on

flywheel/flex plate. The signal generated provides engine speed and

crankshaft position information to PCM. The PCM uses this information

to determine proper fuel injection and ignition timing.

When a flywheel/flex plate slot passes the crankshaft

position sensor magnet, output voltage of the Hall Effect sensor goes

high (5 volts). When the metal between the slots is aligned with

sensor, output voltage goes low (.3 volts).

This high/low voltage signal is sent to PCM each time one of

the slots passes the crankshaft position sensor. The PCM uses this

information to determine when to energize the injectors for fuel

delivery to the proper cylinders.

Ignition Circuit

When ignition switch is turned to the ON position, the PCM

receives a signal that the ignition circuit has been activated. The

PCM will start monitoring input signals.

Manifold Absolute Pressure (MAP) Sensor

The MAP sensor is mounted on engine compartment firewall. The

MAP sensor is used by PCM to calibrate amount of air/fuel mixture

supplied to the engine. This sensor measures manifold absolute

pressure. Ambient barometric pressure is also measured when ignition

switch is first turned on, during engine cranking, and at wide open


The MAP sensor transmits a low voltage signal (1.5-2.1 volts)

at idle when manifold vacuum is high, and a higher voltage signal (3.

9-4.8 volts) during open throttle when manifold vacuum is low.

Input voltage (from the PCM) to MAP sensor ranges from 4.8-5.

1 volts. Adjustments made as a result of this input will usually

affect injector pulse width, ignition timing, idle speed and upshift

indicator light.

Manifold Air Temperature (MAT) Sensor

The MAT sensor is located on intake manifold, with sensor

element extending into the air stream. The sensor measures the

temperature of air entering the intake manifold. This sensor provides

an analog voltage signal to PCM. This signal is used to compensate for

changes in air density due to temperature.

The MAT sensor is a Negative Temperature Coefficient (NTC)

thermistor-type sensor. Its internal resistance varies opposite with

temperature. At cold temperatures, the resistance is high. As

temperature increases, its resistance decreases.

Oxygen (O2) Sensor

The heated oxygen sensor detects amount of oxygen content of

the exhaust gases and produces a voltage signal. PCM uses this signal

to determine system output signals which control air/fuel mixture.

Variations in voltage signal from O2 sensor serve as air/fuel

ratio indicators. When oxygen content is low (rich mixture), voltage

signal will be approximately one volt. When oxygen content is high

(lean mixture), voltage signal will be approximately 0.1 volt.

The O2 sensor contains a ceramic heater in the sensor

housing. The heater operates on 12 volts. The heater is used in cold

starts to help O2 sensor heat up quicker and to maintain the O2

sensor’s Zirconia semiconductor at operating temperature.

In "closed loop" operation, PCM monitors O2 sensor input

(along with other sensors) and adjusts the injector pulse width

accordingly. During "open loop" operation (cold oxygen sensor), PCM

ignores O2 sensor input and adjusts injector pulse width to a preprogrammed

value based on other sensor inputs.

Park/Neutral Switch

On vehicles equipped with automatic transmission, a gear

position indicator signal is sent to the PCM when gear selector lever

has been moved to the Drive range. This signal comes from the

park/neutral switch (neutral safety switch on AW-4 transmission) and

allows the PCM to adjust idle speed, fuel injector pulse width, and

ignition timing advance.

Power Steering Switch

On 2.5L with power steering, a power steering switch is used.

The switch is located on pressure line, next to power steering pump.

The power steering switch sends a signal to PCM when system

pressure rises to greater than 250-300 psi (17.6-21.1 kg/cm ) when

engine RPM is low. The PCM, through IAC motor, will then increase idle

speed to prevent engine stalling.

Serial Communications Interface Receive

The Serial Communications Interface (SCI) receive circuit is

the serial data circuit that is used when diagnosing vehicle with

Chrysler’s Diagnostic Readout Box-II (DRB-II). The PCM receives data

from the DRB-II through this SCI receive circuit.

Speed (Cruise) Control Switches

The speed (cruise) control switches provide 3 separate inputs

to the PCM. The ON/OFF switch informs PCM that speed control system

has been activated. The SET switch informs PCM that a set vehicle

speed has been selected. The RESUME switch informs PCM that the

previously selected set speed has been selected.

Start (Cranking) Signal

The start (cranking) signal from starter relay signals PCM

when starter is engaged. When PCM determines starter is engaged, it

begins to monitor inputs from crankshaft position sensor and camshaft

position sensor.

The PCM uses these signals to determine spark timing and

whether the first fuel injection should occur at cylinder No. 4 or 1

(4-cylinder) or cylinder No. 3 or 4 (6-cylinder). Once synchronization

has been established, the PCM energizes the proper injector and

provides the ignition output needed to start the engine.

Camshaft Position Sensor

The camshaft position sensor is located in distributor. This

Hall Effect type sensor works in conjunction with engine speed signal

of crankshaft position sensor providing PCM with inputs necessary to

establish and maintain proper fuel injector firing order.

When leading edge of pulse ring enters the sync signal

generator on the camshaft position sensor, the resulting change in the

magnetic field causes a 5-volt reference signal to be induced. On 4-

cylinder engines, this indicates to the PCM that piston No. 4 will be

the next piston at Top Dead Center (TDC). On 6-cylinder engine, it

indicates that piston No. 3 will be at TDC.

When trailing edge of pulse ring leaves the sync signal

generator on the camshaft position sensor, the resulting collapse of

the magnetic field causes reference signal to drop to zero volts. On

4-cylinder engines, this indicates that piston No. 1 will be the next

piston at TDC. On 6-cylinder engine, it indicates that piston No. 4

will be at TDC.

Throttle Position Sensor (TPS)

The TPS is mounted on throttle body and monitors opening

angle of throttle valve. It contains a potentiometer operated by the

opening and closing of throttle plate. PCM uses TPS input signal to

determine throttle position under all operating conditions and adjust

fuel injector pulse width and ignition timing accordingly.

The PCM supplies a 5-volt reference signal to TPS. The TPS

output voltage (input signal to PCM) represents throttle blade

position. The TPS output voltage varies from one volt at minimum

throttle opening (idle) to 4 volts at wide open throttle.

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Maby this is too simple but I chased a problem like this last year I almost got into the motor I'm 50 yr old mechanic,my pop says to open the hood in the dark lowand behold the wires were bad lite show all over theay looked great but were badd ??? :nuts:

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Replace the cable going from the negative terminal of the battery to the block. Clean both connections real well. Get the cable at Autozone that has a second wire that runs from the battery side and bolt it to the inner fender. Replace the ground braid from the back of the block to the firewall.

This worked for my problem. If it works for yours we might as well sticky it. It seems to be happening to a couple people with XJ's in my area.

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list of new parts


positive batt cabel


negitiv battery cable


o2 sensor






idle air


mapp sensor


mapp sensor controler




egr valve


pvc tubing and all related vacume lines




all parts are new mopar parts


all old parts have been checked and installed in outer rigs with not change to there running

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the truck owner is a ground free also a eletricain by trade


there are 5 i kid you not 5 engin to body grounds 3 body to batt 2 batt to engine


You might feel this is enough. It absolutely SHOULD be as long as they are done correctly and are making a good ground. Pull a couple off and be sure there is nice clean metal between the strap and vehicle. Then add some dielectric grease!!


When diagnosing a problem, look at/for the clues. Always remember, new doesn't always mean right or fixed. While edundancy can be a good thing, something else to remember is. If someone does something wrong a thousand times its still done wrong. Get it?? Here is one I like.. "I done cut that board three times and its STILL short!!" :roll: :eek: :D


Good luck,


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