So here is the situation. I have an 89 wrangler with 4.2 and its manual. Was having some backfiring issues last year and then she finally died one night. Turns out there was some sensor, computer issues that was messing the carb up. So I replaced the complete exhaust ( cats were destroyed), replaced the carb with a weber 36, did a nutter and removed all the smog stuff. Ran beautiful for months. Then one day I come out of work and it runs like its on 3 cyl, will barely move on its own power and shakes horrible. Didn't have time to work on for for a while but would start it up now and then with same result. One day a couple months ago I started and it ran fine. Wife and I took it around the block a few times with no problem. Parked it started it severl times since with same rough runnin issue. Does it sound like something in the ignition? Maybe the ICM? Thinking of putting a D.U.I on it if it seems to be ignition related but the the reason I am leaning to that is that the one day it ran fine. Any thoughts or suggestions?
Just my quick input. I had a very similar sounding problem and couldn't figure it out for over a 3 weeks even with a friend of mine whose a mechanic coming over 2 or 3 days a week to test it. I had done no engine work recently and had just got done replacing both fenders. Some how sitting in my garage for a week while i was doing body work one of the valves broke so only three cylinders fired. We found that if you pulled the fuel injector wiring one at a time you could figure out which cylinder isn't firing really easily and also by swapping a known good with another one you can see if it the wiring or cylindar and testing the bad one(if any) on a known good cylinder you can really narrow it down
the interrmittant issues are difficult to track down. Its either fuel, spark, or timing. You have a new coil and with the nutter you've eliminated most of the vacuum issues. A HEI setup makes sense and getting rid of the ignition module all together. Those things were a PIA. If nothing else it will not be wasted. The HEI will make it more reliable too.
When I was helping my buddy get his '81 CJ-7 going we had a similar situation with his 4.2L 258. We put a Weber 36 like you did and it would idle great, especially after we grounded everything properly but it didn't have any power at all once you put it in gear and tried to go. Well we finally pulled the valve cover and found 4 bent push rods. We replaced those and then it popped really bad. Then we replaced the timing chain and it did the same thing. We finally replaced the cam and lifters and now it runs like a champ.
I would pull the valve cover and see what's going on in there.
So I went out weekend before last to tear into it. Before I started I just went over everything making sure all the vacuum lines looked good, all the linkage on the carb is moving freely and all the plug wires are on tight. Then I fired it up to verify that is was still running bad. Fired up and idled smooth as could be.
Took it for a ride for about 10 minutes with no problems, ran great. When I was on my way back I was slowing to stop at a stop sign when the break pedal gave and went to the floor. So I baby it home to check it out and find the steel brake line going from the master cylindar to the rear of the jeep had a bad rust spot under the jeep and blew a hole. So fixed the brakes this week and took it for a test drive last night.
Fired up and ran great again, got about 200 yards from my house and it started sputtering/misfiring again. I limped it back home shaking and sputtering at walking speed (as fast as it will move).
I dont even know where to look. I wonder if it has something to do with the carb. Would an accelerator pump do this? I re-checked and I have a the Weber 34 DGEC. Or does it sound like something in the distributor? How can I verify since both would be expensive to swap just to test?