I have a 4.0 I6 that we did an upper end rebuild on and has been running great.

It has the recommended EVERYTHING. We went through and checked all the fuses and relays and they are all good. It's so strange the way this went down, because it has been running like a top and he turned a corner and it started sputtering. It makes me think a wire has worn through the insulation somewhere because it acts like it is an electrical issue. Coil gone bad maybe?

Suggest fuel pressure test, can leave guage hooked up and routed so it can be seen while driving Jeep .. Keep in mind inadequate fuel pressure or faulty fuel injectors can mimic misfiring spark plug(s)! .. Check the injectors right at the throttle cable bracket for rubbing., chafing wire connector .. PO138 'could' be related to injector fault .. Ignition coil failure is common but usually results in no start... All we can do is offer some suggestions as to what the problem 'may' be .. Good luck with it! .... (engine-codes.com)

Funny you should mention fuel supply because we were talking about that last night. We are going to check into all of the wiring at the injectors and the fuel pressure next. Thanks for the help pushrod!!

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Hey Pushrod, sorry to bother you again, but we have check d quite a few things since we chatted last. We checked the fuel pressure and we are @ 38 lb at idle and 40 when driving. We checked all of the injectors and they are getting current. I checked all the plug wires individually and all are firing. One thing that was odd was it seemed to run better on 5 than 6 cylinders when we had 5 and 6 unplugged. We cleared the codes and drove it again and now we are getting P0300, P0305 and P0306. Do you think it might be the camshaft position sensor? All of the wires are connected good and seem to be in good condition, but I'm wondering if it might be the camshaft position sensor itself.

Check distributor shaft for ANY lateral (side to side) movement with engine warm... Replace distributor 'assembly' if any movement found! .. Double check firing order... 1-5-3-6-2-4 clockwise on dist cap... Test compression on 5 & 6.

I'll check that next. We replaced the cap ( the nodes were grooved ) and the rotor and even replaced the cam positioning sensor with no luck. If it has any lateral movement, replace the distributor assembly? I'll have to see if Autozone has a compression test tool. Surely they do. Do you think #5 and #6 would have suddenly lost compression? It was running like a top when it suddenly started missing, which is why I thought it was electrical.

*ANY* lateral distributor shaft movement 'at all' is not acceptable! .. Possibly why cap and rotor were damaged .. Head gasket can suddenly fail between two adjacent cylinders at any time ...... IF the engine has 'proper' compression - fuel delivery and ignition spark with NO vacuum leaks .. Engine has got to run correctly .. Good luck with it!