Topic: Bad hesitation when cold

[Steve-0]

Yes, there were no codes. (Just the power steering code of course)

[Steve-0]

I mean the air conditioning code.

[Steve-0]

The hesitation or what I would now call a "rough spot" (as it runs a little rough) is between 2200 and 2800 RPM. No longer does it drop significantly in RPMs as it did at the 4.0 tb install, but still has the rough spot. And after replacing the TPS, it still remains. I am going to just rule out the cheap stuff, as I need to finish the tune up anyway, and replace the cap/rotor/wires. They all looked fine but you never know. Then I thinj the MAP sensor may be the next one to check. Based on what it does, that makes the most sense to me if the tune up doesnt fix it. Does anyone think its distributor related? Hope not.

[sharpxmen]

Ok, replaced the TPS and it still has the same effects. I guess I need to try a few other sensors and see if that helps. Keep doing that until the stumbling stops. Again, its mostly a slight stumble. Almost feels like when you get a strong headwind hitting you, but its not that for sure. Its not like the bucking you'd get if you were running out of gas (know that feeling too well). I need to go back in this thread and look for the other culprit sensors. I think they were, AIS, O2, crank position and temp sensor right?

AIS won't make a difference there, all the other could. btw, there is also quite a bit of difference between a "slight stumble" and "bad hesitation". I would check the spark plugs, wires, distributor cap and rotor as well since it could be spark related too (as a matter of fact start from there since checking those won't cost any money)

[Steve-0]

Replaced cap, rotor, plugs and TPS. It seems that the stumble or rough spot has reduced slightly but I think its still there. I have been trying to reproduce the effect and it almost seems to me like the gas pedal needs to be let off just slightly enough to not speed up. Just enough to keep it at the right speed/RPM range. It also seems to me like it happens only when the shift light comes on. Now, this may be a coincidence but the shift light will also come on when it feels the gas pedal push down and it is at the right RPM range to recommend a shift. Now it also comes on what seems to be like a bit early (around 2200 RPM) and can stay on until I go over 3000 RPM. Does anyone know what the standard "shift time" is on these things? Does everyone elses come on at that time? I dont know. Its a bit weird. Non the less, I still feel the rough spot, but now I can pinpoint it more to an ascending motion (if that makes sense). Because If I hit the gas, it goes away, well, it seems that way.

[sharpxmen]

Replaced cap, rotor, plugs and TPS. It seems that the stumble or rough spot has reduced slightly but I think its still there. I have been trying to reproduce the effect and it almost seems to me like the gas pedal needs to be let off just slightly enough to not speed up. Just enough to keep it at the right speed/RPM range. It also seems to me like it happens only when the shift light comes on. Now, this may be a coincidence but the shift light will also come on when it feels the gas pedal push down and it is at the right RPM range to recommend a shift. Now it also comes on what seems to be like a bit early (around 2200 RPM) and can stay on until I go over 3000 RPM. Does anyone know what the standard "shift time" is on these things? Does everyone elses come on at that time? I dont know. Its a bit weird. Non the less, I still feel the rough spot, but now I can pinpoint it more to an ascending motion (if that makes sense). Because If I hit the gas, it goes away, well, it seems that way.

what happens if you try to reproduce that with the vehicle stopped (just using your throttle) - can you feel the engine vibrating/shaking at a certain rpm? also, did you change your spark plug and coil wires (since you replaced everything else).
Can't really understand what the symptom is but guessing by what you describe that you have some sort of interruption like all of a sudden 1 cyl would stop working at a certain rpm (like a misfire of some sort) and which goes away once you start accelerating - is that what the behavior is?

my shift light was never correct, but it is most likely because i had larger than stock tires with stock r&p ratio in my axles - so i quit paying attention to it - i wouldn't use that for any type of diagnosis.

[Steve-0]

Yes, I replaced cap, rotor, wires, plugs and TPS. And like I said before, that drop in RPM I was having at 2500 RPM has stopped, but I am left with the rough running area between 2200 and 2700 RPM. Coincidently that is usually also when the shift light is on. I have not tried to reproduce the symptoms while sitting still yet. I think its easier to feel the stumbling sensation while driving that trying to feel the motor move when sitting still, but I will try it anyway. The best way for me to describe the "rough running spot" is that it feels like I am running out of gas, but on a much lighter scale. The stuttering is like a misfire. Like I need a tune-up. But that has already been done. Sorry I am not able to describe this to you in greater detail. I wish I could record it but its the feeling that you get, nothing that you could see.

[sharpxmen]

Yes, I replaced cap, rotor, wires, plugs and TPS. And like I said before, that drop in RPM I was having at 2500 RPM has stopped, but I am left with the rough running area between 2200 and 2700 RPM. Coincidently that is usually also when the shift light is on. I have not tried to reproduce the symptoms while sitting still yet. I think its easier to feel the stumbling sensation while driving that trying to feel the motor move when sitting still, but I will try it anyway. The best way for me to describe the "rough running spot" is that it feels like I am running out of gas, but on a much lighter scale. The stuttering is like a misfire. Like I need a tune-up. But that has already been done. Sorry I am not able to describe this to you in greater detail. I wish I could record it but its the feeling that you get, nothing that you could see.

well, let us know if you get some sort of vibration/misfire while stopped - there could be a few things but what i am wondering is if you get this at a certain rpm like you said or if it's more related to the vacuum in the intake (and if you know where i'm aiming is the map sensor) - that one you can monitor with a multimeter but keep in mind that when you suddenly accelerate your vacuum goes towards 0 (so your voltage will go towards 5v) and then the more rpms you get the more vacuum so the voltage will decrease - what you want to look for is when you keep a certain position of the throttle and the rpms are steady at 2200 (or wherever you bad spot is) that your map sensor output is also steady and not making jumps up/down - and from there when slightly accelerating it will increase and reverse for closing the throttle.

could also be fuel related but in that case i'm thinking that you would get it at other rpms as well - map makes sense in this case but this is me guessing based on what you describe, can't be certain - i would test it though first - better if you have a vacuum pump and gauge to test it with your ignition on and the engine off (not started), hook up the pump to the map vacuum line and increase the vacuum slowly while you monitor the output - if your vac gauge is steady and your voltage output is not or you have a spot where the voltage is not what it should be then you found the problem (you can find the output table somewhere if you do a google search but most likely will be in kpa which is kilopascal and you'll have to convert it)

some auto parts stores rent out tools and they might have a vac pump there, could be worth a try - or you could also get a junkyard one and ask the guys there if you can try it out to see if that's your problem, most of them would let you do that with the map sensor since it's an easy check

[Steve-0]

Well, I just went out and replaced the MAP sensor and still with no resolve. I tried to reproduce the effect while sitting and all I could hear/feel was a slight backfire in the muffler at random. Its so slight but when something like that travels up through the soft suspension and the lift, it gets amplified so I can feel it stumble a little bit. Its really just an annoyance rather than a real problem. I surely do not have any performance issues, cuz this little YJ can really get on it with no trouble at all. I gapped all the plugs at factory specs (that would be where I would have first started, then cap rotor and wires). And replaced TPS and MAPS sensors, I am at an even bigger loss. What gives? Whats worse is that I am obviously having a hard time trying to describe the problem so that I can get some help here. Come to think of it, I get that nasty hesitation when its cold as well, but is gone after it warms up. Or maybe the effect I am having is just much worse when cold. Either way its annoying.

[FourbangerYJ]

Could the problem be on the fuel side not the ignition side? 

[Steve-0]

I thought about that too, but if it was a fuel problem, would I be having this problem only in an RPM range and sporadic at that? I feel like its just something real simple and we are just beating around it. (happens to me all the time) Does anyone think it could be the fuel filter? It looks relatively new. The wear on the bolt heads on the straps look like it may have been replaced not too long ago.

[sharpxmen]

I thought about that too, but if it was a fuel problem, would I be having this problem only in an RPM range and sporadic at that? I feel like its just something real simple and we are just beating around it. (happens to me all the time) Does anyone think it could be the fuel filter? It looks relatively new. The wear on the bolt heads on the straps look like it may have been replaced not too long ago.

if it was the filter i would think that you'd see that problem when you floor it and not the other way around (meaning when you are in need of more fuel), but you say it goes away when you push the pedal - this would be the obvious logic but you never know. I can make other suggestions but i really don't want to be the cause of you going out and buying another sensor and end up at square zero again (i would return the MAP sensor if i were you, of course if the store would take it back).

[Steve-0]

UUghh! This is annoying. I cant take it back. CarQuest policy that if you plug it in, you cant return it. But, I guess they would never know if I did or not. But I am a regular there. I might need to go to a different branch. Did anyone figure out what the original posters problem was? Maybe mine has something to do with his problem? I didnt check before typing this so sorry if that had already been resolved.

[sharpxmen]

UUghh! This is annoying. I cant take it back. CarQuest policy that if you plug it in, you cant return it. But, I guess they would never know if I did or not. But I am a regular there. I might need to go to a different branch. Did anyone figure out what the original posters problem was? Maybe mine has something to do with his problem? I didnt check before typing this so sorry if that had already been resolved.

well, that's why is best to test the sensor first or get a wreckyard one so you don't waste money. What year is your Jeep btw, i can't remember if you mentioned it or not.

so to recap - you have a 4.0 t/b, IAC (AIS) complete from the 2.5, tps from the 2.5, replaced the tps with a new one (for the 2.5 i assume) new dist cap, rotor, wires and spark plugs and the last addition is a new MAP sensor

the only improvement you had so far was that the rough spot is not as bad once you changed the ignition parts - correct?

when did it all start happening (when did you first notice the problem)? any specific event that you can correlate the problem with? was it right after changing the t/b with the 4.0L one?

[Steve-0]

Well, the problem out here (Portland, OR) is that there are no Jeeps out here, just a bunch of XJs in the junk yards. So I didnt have any to test. That aside, it wasnt that big of a deal, it was only $30 at CarQuest. Anyway, I think it has been doing this since I bought it. THere were so many things this Jeep needed tinkering on and this is one of the last one, besides the bump steer correction/alignment issue. Its a 92 2.5 with 154k and I think you guys figured it may have a 3-4" lift. I have the shackle reversal done on the front and have nasty bumpsteer. No drop pit arm, no trac bar, no sway bar, no control arms. But I have the 4.0 TB and spacer, transfered the AIS and the housing as well as the TPS from the 2.5 with that conversion. cold air intake, flowmaster all with 4:11 gearing and 32/11.5/15 Wild Country XTS. Replaced the cap, rotor, plugs, wires, TPS and now I can ad the MAP sensor. The trouble I am having is sporadic and is hard to figure out. All I can say is that it feels like a misfire that causes the thing to buck and stumble just a little bit. When I sat in the garage and messed with it while sitting it made the misfire osunds that sounded like it was coming from the muffler but they were real minor.