Bucking Jeep!

This may be little long but i've been working thru a bucking issue with my 90 XJ 4L AW4 231

The damn thing bucks at anything over 1900rpm while trying to hold a constant speed or slowly decelerating. I've also noticed it slightly thru all gears during slow acceleration tho it's almost unnoticeable as it shifts to the next gear just as it hits the problematic rev range with that kind of pedal pressure. Mashing the pedal through the rpm's no problem. Decelerating with foot completely off the pedal no problem. Rev slowly thru or hold at any rpm in N or P all is good.

Searching the forums I've checked some of the usual suspects:
-TPS needed minor adjusting. Input was just shy of 5v and adjusted easily to approx 4.15 (did it all with analog meter) No dead spots found.
-O2 sensor was changed last time it was e-tested. Due to the fact it bucked before and after it was changed and that revs hold smoothly while in P or N makes me think it's OK.
-Fuel filter
-Distributor indexing looks good. While i didn't actually remove it everything looks to line up right. It didn't do this for 2 or 3 years after I rebuilt the engine so i wouldn't think it's an issue.
-Adjusted the TV cable and it just shifts more firmly.
-Power or comfort mode makes no difference.

I'm going to check the torque converter bolts and i'll check the flexplate while i'm in there too. I guess i'm wondering if i'm on the right track starting now with the tranny. I don't have a garage at home anymore (sob!) which makes this whole process slow so I want to get some advice before I load up and head over to my parents this weekend. Took my dad for a ride tonite and he's thinking it's tranny related from the feel of it. I know squat about transmissions so got some reading to do

Would low fuel pressure or volume cause this? I know the rail pressure drops quickly when it sits sometimes not even giving a drop out the check valve. Is it possible my regulator is letting too much fuel through when it's in higher demand? I don't have a fuel pressure tester but we have plenty of different pressure gauges lying around so if anyone can tell me how to make one much appreciated. I did bypass the ballast resistor tonite which made no difference.

other stuff changed/regularly maintained that has made no difference:
-cap, rotor, wires and plugs
-grounds and connectors clean and coated with dielectric grease
-charging system good-newer alt-made battery cables and ground lines like 5-90's
-Throttle body spotless as always
-K&N filter good to go
-all vacuum lines tight and sucking away
-run BG44K thru it every now and again

That's about it. Am I on the right track or any other ideas?

All of my jeeps are manual trannies, but I have experienced similar problems related to either a bad plug or an arcing ignition wire. Also had this kind of bucking on a bad distributor on an older carburated jeep. These tend to show under load. I know you mentioned addressing these, but worth rechecking.

I went through the same list you have, I even found where my front harness to the O2 sensor, knock sensor and engine temp. sender had cooked on the exhaust and repaired that. Checked my O2 sensor heater wiring and relay.
On a hunch I popped an old O2 sensor in there and the problem disappeared.
A new O2 sensor and the bucking stopped, but the motor would idle high low high low in like a 1 minute cycle. O2 sensor number three has been doing well for a few years now.
Most anytime the motor bucks (in my experience), it's likely to be because it is running lean, for whatever reason or the timing is off. Timing is likely to be either the distributor, the indexing or the TPS. Remember the TPS is two halves, the half closest to the TB is for the engine controls. The half you tested is for the tranny. I haven't found distributor indexing to be all that critical, the Renix compensates. I indexed mine anyway.
One thing I did notice when my O2 was acting up, is the motor wouldn't reach anywhere near redline in top gear, now that is no problem.
It's possible it is a cross fire, one spark plug cable arching to another and firing a plug at the wrong time. Or arching inside the cap. I've had the caps arch before and leave what looked like a black spider web trail inside. But it really didn't buck when this happened, it would just kind of crap out at higher RPM's. And occasionally miss at idle.

thanx for the responses

pec50: What should I look for in the distributor? Imagine you're referring to the mechanical aspects of it. Read about rotational play but never found out how many degrees of play is acceptable and what's not? Gonna search again but if any advice.

8Mud: A few of your posts turned up in my searches-were definitely helpful.
The front harness doesn't look roasted anywhere I saw but I'll have to take a closer look to be sure.
My engine rpm does cycle very very slightly when warm. Idles at @750 cold and much lower at the first line when warm. Its a low but smooth and strong. As far as redlining it as long as it's aggressive acceleration it doesn't buck and will accelerate thru the range. Anything after 1900 rpm with a light acceration, constant throttle or light deceleration it will buck. I have been thinking a spare O2 sensor may be in order for testing tho just to make sure.
I just replaced the Champions i had in in it with NGK's and the Champions' insulators were clean and light tan colour so i don't think it's running lean or if it is not by much. No arching anywhere and no trails inside the cap.

Anyone have any opinions on the fuel pressure? I'm going to get around to checking it but it someone thinks it could be related I'll check it out sooner than later. Is the demand for fuel under load/driving higher than running in P or N at the same rpm?

success!! flexplate to torque convertor bolts were loose. torqued 'em down and all is good.

since it was in a garage i checked the front harness under the manifold and replaced the coolant temp switch. Also used my bros' digital multimeter to set the TPS since i had used my analog-was a little off but now there's not enough o's in smooth!

Eagle posted up on the loose torque converter bolts many times. I checked mine the last time I did the rear main seal. Also a good time to check for cracks in the fex plate, you can see pretty good from the engine side with back main cap off and the other stuff removed.
Glad you were succesfull, it can sure enough get frustrating.
Seems logical the flexplate wobbling around could cause some erratic CPS signals. That's one I haven't had to deal with yet.

jordo said:

success!! flexplate to torque convertor bolts were loose. torqued 'em down and all is good.

since it was in a garage i checked the front harness under the manifold and replaced the coolant temp switch. Also used my bros' digital multimeter to set the TPS since i had used my analog-was a little off but now there's not enough o's in smooth!

Click to expand...

Really? That actually fixed it?

yep