Topic: TJ Running Weird

[JFortner5]

Ok, I thought maybe my exhaust leak was making the Jeep run a little funny. I had a little free time at work so I took the clamps off and welded it up. I didn't realize how loud it was until I drove home today, nice and quiet.

I am still having an issue that I don't really know how to fix. When the Jeep is cold, it runs bad. It has a bad hesitation/stumble until it warms up a little. I just let it warm up for a couple minutes before I take off. On a couple occasions, like today, when I start it up it idles rough. It will start and run fine for a minute, and all of a sudden the rpm drops to 500 or maybe a little less and it kind of surges. I just gave it a little rev and it seemed to smooth out a little.

I don't have a CEL on, so no codes to point me in the right direction. I have only had it for two weeks, so I don't know the complete maintenance history, but it does have a new cap, rotor, wires, and plugs. I did discover today that the cat is gutted. I'm sure thats not helping matters any.

If you guys have any input I would really appreciate it. I was thinking about replacing the upstream o2, the TPS, and MAP, but I don't have a bunch of money to throw at it hoping that it fixes the problem. Once its good and warm it runs pretty good except a little hesitation between 2-3k rpm.

Thanks,
Joey

[sharpxmen]

is this a different issue or the same problem as in your other thread? Just asking b/c the description you have here is quite different than the other one.

Based on this i would take the spark plugs out and inspect them. Without a code is hard to pinpoint but based on description I would say either  you have a leaking injector or injectors, a spark issue (plugs, cap, rotor, wires) or maybe the temp sensor is acting up (although in that case you would get a code). The O2 sensor will not work right after you start the engine for about 1 minute, it will be "heating" up to temperature and your PCM will be in open loop, so if it does this right after it starts (I am not by any means suggesting your O2 sensor is perfect).

[JFortner5]

I should have been a little more descriptive but I had my two year old on my lap.

I thought that I might have had a leak at the exhaust manifold giving a false reading to the o2.  The leak was after the upstream o2 sensor, between it and the cat.  The cat had been cut out, and clamped back on.  My guess is that it got plugged up and the previous owner gutted it.  One of the joints was leaking really bad so I welded it up today.  I was hoping it would solve my problem, though I was not optimistic.

I guess I need to pull the plugs and see what they look like.  I'll try to describe the problem as best I can. 

The idle issue:  I started the engine, and let it run for 30 seconds or so.  I always like to to this to watch the oil pressure gauges come up and just to get a little heat in the motor before taking off.  I did it today, and after about 30 seconds or so the rpm went down to maybe 400-500.  It sounded like it was about to die, but it never did.  I let it do it for a minute just to see if it would smooth itself out but it didn't.  I tapped the throttle a little and it revved up normally and settle in at a normal smooth idle. 


Some times, I get in and crank it up and take off much sooner.  When I do this, normally it will get out of the parking lot at work just fine.  When I get on the road it falls on its face.  It never dies, but it just completely stops accelerating.  It only lasts for a second or two and then it pulls through it.  It always drives fine the rest of the way home. 



The hesitation from 2-3k rpm:  This one is not nearly as noticeable as when it happens at idle.  I notice it mostly in 2nd and 3rd gear.  Its just a really slight stumble.  When it gets to about 2k rpm you can feel a little hesitation, almost like hitting a little bump or something.  Its not major, but it is kind of annoying. 


Thanks for the help,
Joey

[JFortner5]

FIXED 

It was the o2 sensor.  Now to try and track down a couple noises, and go wheel it.

[sharpxmen]

FIXED 

It was the o2 sensor.  Now to try and track down a couple noises, and go wheel it.

cool, glad you figured it out - now the question is why you didn't get a code (o2 would trigger a code most of the time).

[Torch_Ind]

cool, glad you figured it out - now the question is why you didn't get a code (o2 would trigger a code most of the time).

if it's within the specified table but not actually reading properly it sometimes won't cause a hard code.

[bpet72]

mine does something similar to that when i'm driving it awhile and I never get a check engine light. The rpms spike for a second then goes away. I usually can power through it but it never happens in the begining. I wonder if its the same thing from the op?