I bought a parts Jeep with just under 100,000 miles on it, mine has 220,000 so I wanted to use the newer engine.

My Jeep is a 94 Cherokee 4.0, 5 Speed Manual
The parts Jeep is a 99 Cherokee Sport 4.0, 5 Speed Manual

I had to swap just about everything from my old engine over to the newer one, nothing was the same from one to the other, they had different wiring harnesses and connections, everything on the serpentine belt area from power steering to A/C, the throttle body, Intake manifold, Whatever that sensor is on the bell housing.

When I started it, it took a while, and still takes a while when its warm, but if the engine hasn't been messed with for a few hours or more it will start right up, but either way it will run fine for the first 20 sec after start, just sitting there idling, then it starts rough idle and sounds like misfiring.

So far I've found out these engines don't need to be timed, I've replaced the Ignition coil, Distributor cap, Spark plug wires, Spark plugs, the sensor on the Bell housing. I changed the oil and other than being very dirty I didn't see any water or coolant.

I'm thinking it may be a sensor on the throttle body that went out, but it worked fine on the other engine.

I've searched and searched for a vacuum leak but all seems good, thought I may have busted a hose or something taking out the other engine.

I sea foamed and cleaned the intake manifold and throttle body before putting them on the newer engine thats in now.

I used a whole can of Gum Out carb cleaner spraying around the engine bay trying to find a leak in the intake or something some where, no luck

I've ran out of ideas, let me know what your thoughts are please. I don't want to give up and waste even more time putting the old engine back in, it leaks oil and smokes lol.

 

Pull the IAC and clean it.

 

Pulled it and cleaned it, there was a little build up.

Still doing the same thing, It will run fine for 20 sec then idle down and idle very rough, then it will compensate and rev higher for a few sec and when it idles back down it will idle really rough till it revs itself back up and the cycle continues, still sounds like it is misfiring.

 

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Did you pull the distributor out at all? Could be off a tooth?

 

Yes, had to swap it out because of the different wiring harness. It would only fit in one way though. I'm guessing because of the computer timing

 

mine sounds like it misfires a little at idle, i havent figured it out yet.. ever think thats why they got rid of the parts jeep? lol

 

lol. It was sitting in his back yard for 2 years and I got it for $100

 

What do you mean it would only fit one way? Did you have the engine at top dead center and the rotor pointing at 5 o' clock when you dropped it in? I think it sounds like you're a tooth off on the timing.

 

it would be awesome if that's the case. I just make sure my #1 piston is at the top and turn the ignition coil to hit the #1 spark plug wire and drop it in right?

 

Well if it's running now, it's close. Try unbolting it, lifting it up and setting it back in one tooth over. It'll either run better, or worse. If worse, trying turning it a tooth the other direction.

 

It does have to be on the compression stroke, best way is to set it to top dead center on the timing mark. Then drop it in. But if it's somewhat running, you cant be more than a tooth off.

 

Yea, I just pulled the distributor out and set it at 5 o'clock for #1 and set the #1 piston on top (Pulled the spark plug and manually cranked the engine till it was all the way on top), now it wont even start.

I know with any other engine it would be good to go right now with perfect timing... Grr

 

OK, tried resetting the timing again. It started and ran crappy. I advanced it 1 spine clockwise and now it runs great. Thanks guys!