You'll have to excuse me because I know absolutly nothing about jeeps. One of my buds has a 90 jeep with a 4.3 (inline 6) that has some work done on it. been bored 30 over got some race pistons in it and stuff. But even before he had it all set up like that it has had problems idling. One day it runs fine and the next day like crap. He's changed carbs 3 or 4 times with the same result. He was talking about taking the F.I. off a ranger 4.0 and putting it on the 4.3. Is that possible. I'm just looking to give him some advise. Thanks for any help I can get him.

Sounds like opening up a can of worms to me..... Need to find out the exact cause of the idle problem... what all kinds of mods does it have?? race pistons?? what compression?? what kind of fuel? I would be leary of anything over 9.5 to 1 with that head.... has virtually no quench if it is the one I am thinking of... ( does not help with detonation if it is close to problems with it ) Air fuel ratio needs to be monitored to see if it is within spec.... if not, well I am not that familar with the set up but I will bet it is speed density, if so ( it may not be ) then I would recommend a SMT 6 to correct fuel, timing curves for the mods made... I would NOT recommend putting the Ford FI on it, that would be just adding complexity.. the SMT6 will integrate into the stock parts ( works on most everything but check with Perfect Power to be sure ) and is tunable with the laptop....
Good luck!!
TJ

put a vaccume guage on it and check that. are the carbs new?? which brands has he tried? do they have electric choke and is he hooking it up? is the timming set right? lots of things have to be right.