You can have an exhaust guy do a pressure test, see how much back pressure you are getting, or, you can get a sparkplug defouler, drill it out so it fits an o2, put your downstream o2 sensor in the defouler, and screw the defouler into the exhaust. This will tell the computer different readings then the upstream. This will tell you if it's a bad cat or bad downstream o2.

 

Put some copper plugs back in it. The platinum plugs on certain engines will make them run like ****. There is no need for platinum in the 4L.

You can try taking that last cat out and driving it around for a bit and see if that "fixes" the problem. If so, replace the cat. You can get a new one at performance-curve or the vendor mudfrog on here for $40.

 

So the cats are brand new, so i would probably rule those out. But a friend of mine says he would try the 02 sensors. I'm not sure how exactly to go about the defouler. Should i just buy one and i have to drill it out to allow the o2 sensor to fit inside of it?

 

If the o2 sensors are bad, they'll typically throw a code.

 

This. If you are certain the cats are good, no need for the defouler test.

 

So you don't think that the o2 sensors would be the cause. You said the jeep was going into a limp mode, what else could cause this?

 

Ok I tried something new. I disconnected the battery to reset the computer. I started it up cold and I listened to the injectors 2 and 6 were clicking but when I unplugged the connectors from these injectors there was no change in the motor. So am I back to the ignition side of things?

 

CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION
Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

 

Change spark plug wires! Have chased problems just like that on several jeeps. Each time it was bad wires. Also, as said, go with regular old copper plugs.

Don't need expensive wires. Just get decent set at store.

 

I'm thinking that it could be something basic. I always make sure I have spark at each cylinder. If you are getting a mis-fire code, I assume that means it didn't fire. You changed plugs but did you see if each plug had a spark? You can first check to see if you have spark just by pulling wires off and then of course, take the plugs out too and check for a nice bright blue spark.

I would then check for good compression at each cylinder to make sure valves are holding.

Next, I would check fuel pressure to see if the fuel pressure drops when you push on the throttle. I had a pump that ran at idle ok but the pressure would drop when you pushed it. Then the engine would backfire out the intake. I changed the pump and it ran like a champ.

I'm thinking that you may hear and not hear the click on the injectors because the PCM is cutting fuel to the injector due to the mis-fires. Not sure about this and there are certainly people that know more about Jeeps than I do.

Keep trying. I always start by assuming the Jeep wants to run and there's just something it doesn't like that's causing it to act up.

 

SOLVED!!!! It was the stupid coil pack rail. It was perfectly fine before the engine swap so I kind of ruled it out. But I decided what the hell do I have to loose bought new one, put it in, and she runs like a charm. Thank you everyone for your input.

 

Glad your problem is fixed!

 

Edit: disregard this post.