Jeep YJ bucking and hesitating when accelerating or under load when hot

[wcox1999]

I have this 1989 Jeep YJ 6 cyl Auto transmission, it has a new carburetor and nutter bypass, new distributor and plug wires. Work was done by previous owner, this is my toad for my RV so it spends time in Florida and time in Washington State. Basically it stutters and hesitates when trying to accelerate or going uphill usually at speeds of over 40 mph and it does this when we have been driving after it has been running for about an hour or is hot. I liveabout 30 minutes from town and have to go up a steep incline and back down and then back. The reverse drive is quite a bit steeper. This problem always seem to occur when I first start the incline and I can usually feather the gas pedal or slow down and it goes away. I then go back down the ridge and almost make itto my drive which again is no a slight incline it starts again but this time it is usually worse and I have to slow way down or pull over and let it sit for amin. I always smell something like gas when this happens and if it does stall, it always starts back up. It seems worse when it is hot outside 90+. I once drove it 100 miles up and down the mountains on an interstate in the morning and it ran great that afternoon the temp hit 90 and I only made it about 40 or somiles before it started again. The crazy thing is sometime if I sit for a bit it goes away like nothing happen. And like I said I always smell and odor like gas.
I have had this for a year and have had it in the shop 4 times with each time the mechanic fixing or replacing something else. It happened much more frequently when I live in Florida a and the outside temp seem not to matter as much as it happen more like if driven for a specific time. I did find a brokenwire on the nutter bypass and fixing that seemed to give me more range.
Any direction would be helpful

 

[greg92jeepxj]

Hello and welcome to jeepz.com. I don't have knowledge of the nutter bypass beyond that it is a modification to the fuel and ignition system on carbureted engines . If you can get any info regarding the nutter bypass with regards to inspecting the mods made to be sure it isn't malfunctioning , that may be helpful . But I will say that your drivability problem seems to be a lean condition . The effects are much like detonation since your experiencing climbing engine temperature under load . This is a result of excessive high cylinder pressure causing cylinder temperature to rise higher than normal. The first suspect is EGR. Inspection is needed to confirm if vacuum is present , valve is operational , passages are clear and not carbonated and the valve Pinole and seat aren't carbonated as well. Ignition timing needs to be checked if spark is occurring in proper time or late as valve timing needs to be checked in the same fashion. If the timing chain has too much slack and valves opening too late and distributor ignition timing off and occurring too late or too close to TDC. Combined with late valve timing. I,state this because I've a feeling this engine is of high milage due to its model year and the driving between Florida and Washington state ? I've a feeling that mechanics have ignored the nutter bypass simply because not wanting to involve themselves with and possibly not knowledgeable and just want to replace parts related to the usual cause in hope it will satisfy somewhat . Curious what was performed by them but probably won't matter much if items like fuel filters and spark plugs and maybe distributor timing checked . Was the EGR serviced at all ? Not knowing what mod is done to the fuel system has me thinking of any possibility of it contributing to a lean condition. But it is my belief that your experiencing detonation under load and these items I've posted should be checked as they can contribute to this condition. Normally , EGR is the strongest but not limited to . BTW , has a knock sensor been checked or changed ? If it is not working right or adjusted correctly , it's like not having one at all. The RENIX system used one so distributor timing is PCM adjusted and knock sensor will affect this. It interests me as well what part the nutter bypass plays in PCM engine management. Not certain due to lack of knowledge of the nutter bypass but I believe the whole concept of the bypass is to isolate fuel and ignition systems from the PCM engine management system to some degree or totally ? This is where it gets complicated and mechanics are of less help by lack of knowledge or by choice. I would still advise to check what items I've posted especially EGR since they're separate from the bypass and potential players . Hope this helps and wishing good luck on this problem. Post back questions and work and progress performed when able . Thank you for your membership here at jeepz.com