Stuttering from 1500-2100 - JeepForum.com
 
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post #1 of 13 Old 08-18-2017, 03:14 PM Thread Starter
Wolf427
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My '96 XJ(4.0, AW4) has a new issue, stumbling/stuttering/stalling between 1500-2100rpms, usually between 60-80KPH. Idles perfectly. No 02 sensors or cat(been like this for over 14 months, that is not the issue). MAP and AIC tested.

Issues started a week ago, it started to stumbled when accelerating to 100 on the highway, then it started getting worse until last night I could barely drive.
Figured it was the TPS, so I replaced it.
Once replaced, I was able to drive more, there is a lot less hesitation/stuttering, but it will do it every time once the engine is warmed up and I drive between 60-80kph at 1500-2100 rpm's.

I swapped the new BWD TPS with another to make sure it wasn't faulty, and the issue is still there.

Sensor reads 780(+/-025)mv at closed throttle, and 4.86(+/-10)v at WOT.

PCM was reset after install, and there were never any CEL's(before or after).

UPDATE: It bogs really bad at 1500rpms when doing 80kph(50mph), and will start backfiring. I can smell unburnt fuel in the exhaust.


Any ideas?


Betty '96 Cherokee Sport 4dr
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post #2 of 13 Old 08-18-2017, 04:29 PM
scxj
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780mv,+/- 250mv fully closed seems high voltage wise. that suggests that there is added resistance in the ground leg of the sensor. Either the TPS is faulty or your ground connections are inadequate. Can you measure the resistance to ground from the connector the attaches to the TPS? I suggest you place one ohm meter lead on the negative terminal of the battery terminal and the other on the ground pin off the TPS connector. It should be less than .5 ohms. Be sure the flex the wires of the sensor cable while measuring. if its greater than .5 ohms try cleaning the ground connections to the chassis/engine and the PCM module. These sensor cable connection have a tendency to be intermittent. be careful not to jam a over sized probe into the connector or you will created another problem for yourself.. good luck. it might be a good idea to disconnect your battery while ohming out this connection. if voltage is present while making resistance measurements you could damage the meter.
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post #3 of 13 Old 08-18-2017, 06:34 PM Thread Starter
Wolf427
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Quote:
Originally Posted by scxj View Post
780mv,+/- 250mv fully closed seems high voltage wise. that suggests that there is added resistance in the ground leg of the sensor. Either the TPS is faulty or your ground connections are inadequate. Can you measure the resistance to ground from the connector the attaches to the TPS? I suggest you place one ohm meter lead on the negative terminal of the battery terminal and the other on the ground pin off the TPS connector. It should be less than .5 ohms. Be sure the flex the wires of the sensor cable while measuring. if its greater than .5 ohms try cleaning the ground connections to the chassis/engine and the PCM module. These sensor cable connection have a tendency to be intermittent. be careful not to jam a over sized probe into the connector or you will created another problem for yourself.. good luck. it might be a good idea to disconnect your battery while ohming out this connection. if voltage is present while making resistance measurements you could damage the meter.

I didn't check the ground connections but I will make sure to. I real in the service manual it should be higher than 200mv, but it didn't give a range.

Forgot to mention I clean my throttle body and IAC as well.

Also, new update. Engine bogs the worst while doing 80kph when the trans shifts and I sit at 1500rpm. It actually started backfiring as well. You can definitely smell fuel when it starts to do this.

Betty '96 Cherokee Sport 4dr
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post #4 of 13 Old 08-19-2017, 07:23 AM
CJ7-Tim
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Quote:
Originally Posted by Wolf427 View Post
... No 02 sensors or cat (been like this for over 14 months, that is not the issue). Any ideas ?
Yup, install a cat and some O2 sensors.


What are miles per gallon/kilometers per liter is it getting ? I would guess that mpg's are about 30-40% lower than normal. If the PCM does not have O2 sensor data it will either remain in open loop/warm-up mode, or default to limp mode. Either one means it is running full rich, and it will probably be bucking/backfiring/stalling, and you would likely smell gas fumes in the exhaust.


Once you have that taken care of, install a genuine Jeep TPS, the BWD is out of specification.

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post #5 of 13 Old 08-19-2017, 08:21 AM Thread Starter
Wolf427
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Quote:
Originally Posted by CJ7-Tim View Post
Quote:
Originally Posted by Wolf427 View Post
... No 02 sensors or cat (been like this for over 14 months, that is not the issue). Any ideas ?
Yup, install a cat and some O2 sensors.


What are miles per gallon/kilometers per liter is it getting ? I would guess that mpg's are about 30-40% lower than normal. If the PCM does have O2 sensor data it will either remain in open loop/warm-up mode, or default to limp mode. Either one means it is running full rich, and it will probably be bucking/backfiring/stalling, and you would likely smell gas fumes in the exhaust.


Once you have that taken care of, install a genuine Jeep TPS, the BWD is out of specification.
The O2's were disconnected last year because they were causing what seemed like heat soak after driving and shutting the truck off. Once those were disconnected the issue disappeared. Those are getting replaced before I do emissions in the fall. I understand those could very well be causing the issue, but after a full year of running without them and now it starts acting up? I highly doubt it.

I am getting 14L/100km(16mpg?). My spark plugs look like it's running lean, but it can't be since I smell fuel.

I am going to try a TPS from napa today. I called the dealership and they no longer sell the TPS, I have to buy a throttle body assembly with all sensors.

I am going to check my dist cap & rotor, spark plug wires, as well as the camshaft position sensor.

Betty '96 Cherokee Sport 4dr
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post #6 of 13 Old 08-19-2017, 09:43 AM Thread Starter
Wolf427
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Checked the new TPS again, here are the readings:

From chassis ground to middle wire(2) on connector- 755mv closed, 3.61v open.

From black wire(1) on connector to red wire(2) on connector - 755mv closed, 3.50v open.

If I measure the middle(2) wire, I get 4.25v, if I measure the last wire(3) I get 5v.

Betty '96 Cherokee Sport 4dr
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post #7 of 13 Old 08-19-2017, 10:26 AM
CJ7-Tim
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The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the PCM) represents the throttle blade position. The PCM receives an input signal voltage from the 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. The TPS should vary in an approximate range of from .25 volts at minimum throttle opening (idle), to 4.8 volts at WOT wide open throttle.


If you have much variation from the min/max I would suspect poor quality Chinese TPS. Your local Dealership may no longer stock some Cherokee parts, but there are many Dealership websites that will find parts for you, and sell them at a discount.

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post #8 of 13 Old 08-19-2017, 12:40 PM Thread Starter
Wolf427
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Issue seems to have gone away today. Drove about 80km at varying speeds and RPMS. Picked up another TPS from napa, Echlin made in USA. Hopefully if this acts up again, I can swap it and see if things change. Last night it was running very poorly. This morning I took my dist cap and rotor off and check for play, I have about 1/16" of play. But I did move the stator(dist pickup/cam sensor/etc) wire to a new spot(it was bent quite a bit and shoved against the block) and unplugged and replugged it in. Not sure if that had anything to do with it, or it was just a fluke.

I doubt the issue is fixed. I will keep this thread updated.

Betty '96 Cherokee Sport 4dr
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post #9 of 13 Old 08-19-2017, 02:33 PM Thread Starter
Wolf427
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Also, logging manifold pressure, throttle position, and rpm with an app. Also using a new app to monitor voltages of those sensors along with rpm and timing. Hopefully if this happens again, I will be able to see what is going on with those sensors.

UPDATE: Drove to the gf's house. 15 miles, varying speeds. Made sure the engine ran at 1500rpm at 80kph for most of the drive. Still feels like there is a slight issue, but nothing crazy. Had my diagnostics running the whole time, so I have a baseline for it running well.

Betty '96 Cherokee Sport 4dr
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post #10 of 13 Old 08-20-2017, 04:58 PM Thread Starter
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Another drive today and it seems "okay". Really just seems like it's at 80%.

Also replaced spark plugs, wires, and dist cap and rotor.

One other thing I noticed is that it takes longer than normal to shift from 1-2 and 2-3. The rpm's get higher than usual. I have made sure to adjust the throttle kickdown cable, with no change.

Betty '96 Cherokee Sport 4dr
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post #11 of 13 Old 08-21-2017, 02:47 PM Thread Starter
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Okay so more driving done today, around 50 miles. I'm looking at my diagnostics and I am finding something that I think is odd, but I need someone to confirm whether or not it is out of the ordinary. I assume throttle position will change based on engine rpm's but I am seeing it stay the same through different ranges. I will attach a picture of an example from my diagnostics.

Left is Throttle Position %, middle is Timing advance *, and right is Engine RPMs.


Should the throttle position be directly correlated with engine rpm? I.E Higher rpms = higher throttle position percentage? And should it be stable the entire way through, I.E 30% throttle position at 2500 rpm, or is it normal to see the throttle poistion percentage fluctuate at a stable rpm?

Betty '96 Cherokee Sport 4dr
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post #12 of 13 Old 08-23-2017, 09:46 AM
scxj
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I believe what you are describing is either a bad TPS sensor or bad wiring to the sensor.. It seems that you have already replaced the TPS. Have you checked the wiring to the PCM? Have you measured the resistance to ground from the ground pin of the TPS connector while flexing the cable? These connections are ticking timebombs in my experience. I have replaced IAT connector/wires and the TPS connector/wires due to intermittent connections..Its like the factory saves money by making the cabling as short as possible. one more thing, the TPS voltage will affect the shifting of your transmission.
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post #13 of 13 Old 08-23-2017, 03:08 PM Thread Starter
Wolf427
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Quote:
Originally Posted by scxj View Post
I believe what you are describing is either a bad TPS sensor or bad wiring to the sensor.. It seems that you have already replaced the TPS. Have you checked the wiring to the PCM? Have you measured the resistance to ground from the ground pin of the TPS connector while flexing the cable? These connections are ticking timebombs in my experience. I have replaced IAT connector/wires and the TPS connector/wires due to intermittent connections..Its like the factory saves money by making the cabling as short as possible. one more thing, the TPS voltage will affect the shifting of your transmission.
I've been doing a lot of driving to make sure the issue is gone and it seems to be.
I didn't check resistance, but I will definitely do that. I have been logging diagnostics every time I drive to try and catch what's acting weird, if it happens again I will post up. I'll go check resistance and update.

Betty '96 Cherokee Sport 4dr
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