TJ 4.0 Stumble? - Page 2 - JeepForum.com
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post #16 of 48 Old 07-07-2013, 06:30 PM Thread Starter
bmxboy809
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Quote:
Originally Posted by mukluk View Post
If you look up to post #10 above, you'll see a link I posted that will take you to an online-accessible FSM for your TJ.
I will take another look at that, I after looking it over briefly I did not see a section that might talk about that sensor but i will look again.

It doesnt stop bogging down when I put the clutch in, I have to feather the clutch to keep the thing running and drive back to the garage. At idle it is "searching" and stumbling.


Now I have not had the "crank no start" problem but I read that heat can change the performance of the Crank Position sensor. Do these symptoms line up with a failing CPS?

I have also read a little bit about batteries causing gremlins...My battery is kinda old. I had it load tested last summer and it was fine. The jeep starts fine every time and I have not had any other battery issues in the past.

Based on what i have read so far It could be PCM, TPS, CPS, MAP, O2 sensors or any combo of them. They are all expensive parts (40-90$ for the sensors) so I dont want to just buy them all in hopes it will solve the problem. I am in pretty deep already with the ignition parts I replaced.

Ill continue to read the FSM, thanks Mukluk


1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #17 of 48 Old 07-08-2013, 03:14 PM Thread Starter
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Can the CCV cause any of this trouble? what about the catalytic converter? I suppose there is no good way to know if it is bad?

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #18 of 48 Old 07-08-2013, 03:38 PM
FarmerinVA
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Ah yes, the 4.0L engine stumble. If you've searched, you've probably seen a dozen threads on this, all of which end up with different solutions or just peter out without one. Sorry to be depressing but that's what I found when it happened to me.

The collective wisdom seems to be to work from easy/cheap to difficult/expensive, one thing at time: fresh gas, then clean the air and intake system, then check or replace the plugs, etc. I worked down a list, and several things helped incrementally until my problem is now gone. I'm not 100% sure why, really, but I encourage you to take the same systematic approach. Don't do something relatively difficult like replace the fuel pump or O2 sensors (which has been the problem for some people) until you cross the easier/cheaper things off your list.

Here's my brief thread on it: Diagnose stumble? One thing I didn't mention there was to check the vacuum line on your intake pipe to make sure it's not detached, as it comes off easily on the 99.

Good luck, I know how annoying this is.

My do-it-yourself install thread for a TrueTrac in the rear, upgraded shafts, and a PowerTrax No-Slip in the front:

http://www.jeepforum.com/forum/f9/ex...hafts-1234745/
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post #19 of 48 Old 07-08-2013, 07:04 PM Thread Starter
bmxboy809
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So i started by cleaning the throttle body and IAC. They both had buildup but nothing concerning. I took her out for a drive and still had the stumbling, stalling, misfire.

I am going to look into cleaning up all the grounds I see that based on the schematic all of the sensors share a ground somewhere. So thats tomorrows project

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #20 of 48 Old 07-09-2013, 11:42 AM Thread Starter
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I am looking into buying one of the bluetooth OBD2 adapters to use torque on my phone. Does it really matter which el-cheapo adapter I buy. There are some on amazon for 4.99. I didnt see any that I would consider to be "name brand".

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #21 of 48 Old 07-09-2013, 11:44 AM
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Quote:
Originally Posted by bmxboy809
I am looking into buying one of the bluetooth OBD2 adapters to use torque on my phone. Does it really matter which el-cheapo adapter I buy. There are some on amazon for 4.99. I didnt see any that I would consider to be "name brand".
I got a blue one that was $15. Don't know the name but it looks transparent. It's been working just fine.
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post #22 of 48 Old 07-09-2013, 02:10 PM Thread Starter
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Just ordered mine and downloaded Torque. It should be here tomorrow to continue this wild goose chase

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #23 of 48 Old 07-09-2013, 07:04 PM Thread Starter
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I did some more experimenting this evening. I verified that all the sensor grounds have continuity with the negative terminal on the batter and with eachother. So I think the wiring is ok. I just had the IAC apart last night so I thought i would try to run with it disconnected.

Before: misfires and stumbles with any load

shut er down and pulled the plug. Everything ran OK but not perfect. The CEL came on with the sensor unplugged.

I plugged the sensor back in and it continued to run OK but not perfect.

I reset the codes, CEL went off and it ran like crap again.

It would seem like this further confirms the problem exists only in closed loop. So I must have a failing sensor or the PCM itself


Another interesting tid bit is that the only sensor that doesnt seem to have any affect when I unplug it is the upstream O2. Everything is exactly the same except the CEL comes on. My new code reader will be here tomorrow. What voltage should I expect from that sensor?

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #24 of 48 Old 07-09-2013, 07:54 PM
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O2 sensor voltages range between 0.2 and 1.5 volts, anything outside that range should make the PCM throw a code and CEL.
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post #25 of 48 Old 07-10-2013, 12:57 PM Thread Starter
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I did more reading today about the IAC. I made the mistake of pulling mine apart while i was cleaning everything up. Idle seemed fine after i put it all back together. Is the IAC crucial to overal engine performance or just at idle? I think I may need to replace the IAC just to be sure it works ok. Is there any particular readout i can look at in Torque to decide if its a problem?

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post #26 of 48 Old 07-10-2013, 01:31 PM
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IAC is just for idle. Once the throttle is open the IAC will make no difference to the running of the engine.

Online factory service manuals and parts lists - http://www.jeep4x4center.com/knowledge-base/index.htm
If it doesn't work properly, look for the service manual link at the bottom of the page.
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post #27 of 48 Old 07-10-2013, 07:34 PM Thread Starter
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so i got my new code reader adapter tonight and played with it a little bit.

when the motor was stumbling and jerking all to hell the upstream O2 voltage was .8V and the downstream was 0.0. It looks like the downstream voltage is at or near 0 a lot of the time. Is this normal?

so here was my test. I disconnect the downstream 02 sensor. I did not immediately get a code for it. everything ran great! Eventually the CEL came on but it still ran ok. The code I got was upstream o2 high voltage. I plugged the downstream sensor back in and with the light still on it ran good. Then i shut er down, cleared the code and everything seemed fine. I though maybe the issue was gone.

I let it cool down and tried about an hour later. Still jerking/surging/stumbling. I monitored the coolant temp, intake air temp, MAP, and Throttle position. Nothin wacky seemed to be goin on at all....i am still puzzled

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #28 of 48 Old 07-11-2013, 05:07 AM
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Replace the o2 sensor with an NTK unit from rockauto.com. My upstream never threw a code when it went out but I knew it was the problem after running with it unplugged for a couple of days with no stumbling issues.



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post #29 of 48 Old 07-11-2013, 08:05 AM Thread Starter
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The only reason I am hesitant to replace them is that running with the upstream sensor unplugged didnt help. With the upstream sensor unplugged the problem was as bad as ever. so I could spend another 100 bucks on O2 sensors and still have the problem.

If i understand the setup correctly, by unplugging the post cat O2 sensor the target voltage changes for the upstream feedback to some pre determined value? So that explains why i get a code for the upstream sensor when the downstream sensor is unplugged? That makes me question the condition of the catalytic converter if the downstream sensor is reading 0 a lot of the time what does that mean? does that mean the cat is doing its job or that its not?

1999 Wrangler TJ 4.0 5spd -- 6" LA , 35" MTZ's , Ford 8.8 , 4.88 gears , SYE , Tom woods CV shaft
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post #30 of 48 Old 07-11-2013, 08:10 AM
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Quote:
Originally Posted by bmxboy809 View Post
The only reason I am hesitant to replace them is that running with the upstream sensor unplugged didnt help. With the upstream sensor unplugged the problem was as bad as ever. so I could spend another 100 bucks on O2 sensors and still have the problem.

If i understand the setup correctly, by unplugging the post cat O2 sensor the target voltage changes for the upstream feedback to some pre determined value? So that explains why i get a code for the upstream sensor when the downstream sensor is unplugged? That makes me question the condition of the catalytic converter if the downstream sensor is reading 0 a lot of the time what does that mean? does that mean the cat is doing its job or that its not?
If you get no stumble with the back one unplugged, unplug the back one for a day and zip tie the harness out of the way. If no stumble, replace the back one.

By back one, I mean the downstream. Your symptoms are quite similar to when my upstream went out. I don't see why it wouldn't work the same way as when I tested my upstream.

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4.0 , missfire , o2 sensor , stumble , surge

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