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Unread 09-05-2012, 10:56 AM   #1
graysonh
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1999 XJ Cherokee 
 
Join Date: Sep 2012
Location: Mt Pleasant, South Carolina
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99 Cherokee Strange Issue

Hi guys i have a 99 cherokee sport 4.0 I6 auto with 120,000 miles. As of late the jeep has started to buck/ jerk around 40 mph. The rpms will dance all over the place and it will shift rough, can barely get it above 45. And i will idle around 1500 when im in park. The TPS and NSS have been replaced with no change. Engine coming to temp will seem to slightly alleviate the symptoms.

Also, CEL comes on every so often with code for Transmission Range Sensor.

Now, normally i would call it a bad transmission, however when i drive the jeep in the morning or when its cool outside, every single problem goes away. No bucking, no hesitation, and normal idle and extremely smooth shifting through all gears at all speeds.

I am completely stumped with what this would be and any suggestion will be considered. Has anyone had this same problem or is it just me?

By the way, if anyone needs a write up for the NSS or TPS let me know. Thanks

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Unread 09-05-2012, 02:21 PM   #2
CG98XJ
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1998 XJ Cherokee 
 
Join Date: Feb 2008
Location: Connecticut
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I had this same issue, almost identical symptoms. It started a few years ago, and I have replaced about every sensor you can name, injectors, checked compression, new throttle body, checked fuel pressure, changed fuel pump, the list goes on. I cannot even remember what else I have done. I would start with sensors though. It did get better after i changed my CPS and MAP sensor. But did not fix it completely. I dont have many suggestions, but good luck. If you find a fix let me know!


EDIT: Google heat soak, and vapor lock. May give you some insight.
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1998 2door XJ - RE 3.5 SF and 2in teraflex shackle and spacers, 35x12.50 BFG M/T, 15x8 RockCrawler Wheels, AJ's offroad super rails, Nates 4x4 rear bumper, Flowmaster 40 Optima Yellow Top, Currie Enterprise HD Tierod and Draglink and lots of cut sheetmetal

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Unread 09-05-2012, 02:35 PM   #3
graysonh
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Location: Mt Pleasant, South Carolina
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I appreciate it. Im going to look into the MAP sensor.

Quick update, the jerking of the rpms will happen while the car is even stationary. Go out to the car when its hot, put it in D and it the rpms will fluctuate and go crazy then almost die. Pop it in nuetral then back and its fine.

I've never heard of a transmission that slips without even moving haha, i will check the trans fluid tomorrow.
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Unread 09-05-2012, 02:44 PM   #4
CG98XJ
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No problem. I dont remember having the tranny part as an issue for me, but that is strange. Maybe change the tranny fluid and filter also.
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1998 2door XJ - RE 3.5 SF and 2in teraflex shackle and spacers, 35x12.50 BFG M/T, 15x8 RockCrawler Wheels, AJ's offroad super rails, Nates 4x4 rear bumper, Flowmaster 40 Optima Yellow Top, Currie Enterprise HD Tierod and Draglink and lots of cut sheetmetal

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Unread 09-05-2012, 05:19 PM   #5
tjwalker
It's the crank sensor!
 
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Follow the code. Always. OBDII isn't perfect, but it is awfully darn good at pointing you in the right direction.

Post the exact code. With OBD, the devil is in the details.

Then Google search that code + Jeep. For example, PO455+Jeep Cherokee. Usually there are others before you who have experienced your problem.
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Unread 09-05-2012, 05:50 PM   #6
graysonh
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Thanks tjwalker ill get it scanned agian tomorrow and post/ do research on the exact code i guess when i got it scanned at advance the guy just told me it was the transmission range sensor
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Unread 09-06-2012, 10:59 AM   #7
graysonh
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The CEL code is P0705. I googled it and all the problems point to the NSS. My reverse lights and all of that work fine. Could the code be pointing to something else?

Update 2: Whenever its really hot outside and the jeep has been sitting in the sun, whenever i put it in D, the revs stumble then go to 0 and the engine dies. Also, checked the trans fluid today and ive never smelled trans fluid before but i would say mine had a slight old burnt smell to it.
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Unread 09-06-2012, 05:32 PM   #8
tjwalker
It's the crank sensor!
 
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Yes, P0705 is very often related to the NSS. Question for you. Where did you buy the NSS that you installed? No lack of total crap sensors available, both retail and especially the cheap chinese stuff on ebay which you should stay away from like the plague.

For your other issue, two things come to mind. First is clean your idle air control and throttle body. Also test you "throttle position sensor". More on these things below.

What is the COLOR of your transmission fluid? It should be red in color and you are absolutely right in that is should not smell burnt. If you don't meet these conditions, I'd recommend you drain what is in the pan and refill (about 3-4 quarts). Drive a week. Repeat as necessary until fluid stays red and doesn't smell burnt. Use only Dex/Merc III compatible fluid.
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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality

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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is 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. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

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: -

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

• 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 fault TPS can report values outside the denied 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 excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.
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Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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