XJ going Mad-please help

[big sam]

Hi I need some help please?

My xj 4.0L 1998 country
The engine runs very rough and the rpm jumps up and down if you try and keep the pedal steady, and it starts to backfire in the intake. If I floor it, it goes with a lot of power and then chance gears. One thing that I have also notice is when it start with the problem wile I am driving and I turn the ignition off and on quickly it stops the problem for a short while and then the problem comes back again. At first the Jeep only started doing this when it was close to normal operating temp. But now after testing the TPS it is a problem from the word go. It feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears. I still have a strong suspicion that it could be the TPS.

How can I test the TPS at the Computer to see it I get the same readings as I get at the TPS on the intake?

Thanks for all your help!!!
:cry:

[cherokeejim47]

Headed to Jeep Dealer today will quiz Service Manager and Techs on this and advise of result.

[big sam]

Thanks a Mill!!!!:love0007:

[Mudderoy]

Hi I need some help please?

My xj 4.0L 1998 country
The engine runs very rough and the rpm jumps up and down if you try and keep the pedal steady, and it starts to backfire in the intake. If I floor it, it goes with a lot of power and then chance gears. One thing that I have also notice is when it start with the problem wile I am driving and I turn the ignition off and on quickly it stops the problem for a short while and then the problem comes back again. At first the Jeep only started doing this when it was close to normal operating temp. But now after testing the TPS it is a problem from the word go. It feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears. I still have a strong suspicion that it could be the TPS.

How can I test the TPS at the Computer to see it I get the same readings as I get at the TPS on the intake?

Thanks for all your help!!!
:cry:

http://www.fototime.com/78EA763821BA137/standard.jpg

TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (SEE Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1

Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.


Test # 2

You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

TPS

You may have one or more of these Physical Symptoms:

1) The engine loses power and is stalling.
2) The engine will idle, but may die as soon as you press the gas pedal. When driving, it seems as if all power is gone.
3) Sometimes it feels as if the transmission is failed or isn't shifting properly, if at all. If you quickly jump on the gas you might be able to get the transmission to shift, but it won’t shift properly by itself. Shifting manually, the transmission goes through all the gears.

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics. The TPS function should be verified early in the troubleshooting process, when a transmission issue is suspected.

TPS TEST

You should have 5 volts going into the Throttle Position Sensor (TPS). It is best to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. At idle, TPS output voltage should be greater than .26 volts but less than .95 volts. Move the throttle and look for smooth meter response up to the 4.49 at WOT. The other wire will be the ground and should show no voltage.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.


The TPS is sensitive to heat, moisture, and vibration, leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following:

-Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".

- High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.

-Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.

-Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted accordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.

- Engine Misfire: A faulty TPS can report values outside the acceptable range causing the ECU to incorrectly fuel the engine. This is noticeable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessive misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.


:link: (http://www.jeepforum.com/forum/f11/how-test-tps-610386/)

[4.3LXJ]

So is the check engine light on? How long since you changed the o@ sensor?

[BlueXJ]

My first inclination is a vacuum leak. Either a line off or cracked or even loose intake bolts.

[big sam]

Hi I have done the test on the TPS at it was fine no problem there. I would like to measure the TPS where it go's into the computer box but is not sure where it go's into the computer box. I will still do the test on the CPS - Thanks for that test.

The engine light is off.

I can't see / hear any sucking sound for the vacuum but will also make sure about that.

It is always a problem when you buy a car with the problem because you dont know how the problem started in the first place.....and to make it even wors we I stay there in no one the can work on Jeep's. But I am sure with your help I will be able sort it. Thanks All!!!!

[big sam]

Hi I am getting a code reader next week. Will keep you posted. Thanks

[rugidone]

Check your distributor hold down bolt and see if its loose. after that, check the cap for the misfiring. I chased an issue for too long and threw alot of parts at it. Turned out to be what I mentioned. Trans issue, might be related, might not be, it being what it is, if its not seeing the steady increase in the rpms, it probably thinks it shouldnt shift.

[big sam]

Hi
I have got myself a code reader and checked for any codes yesterday and this is what the code reader gives me,

P0700 – Transmission control system
P0753 – Shift solenoid A electrical
P0751 – Shift solenoid A performance/stuck off
P0740 - Torque converter clutch circuit/open
P0122 – Throttle/pedal position sensor/switch A circuit low :confused:
P1694 – No bus message received from ECM mod
P0715 – Input/Turbine speed sensor A circuit

Can this maby all related to the Throttle position sensor?

Thanks :bang:

[4.3LXJ]

Sam, my rule of thumb is that with that many codes, it is almost always the ECM especially with that code P1694. I think a new box will solve it for you.