92 Cherokee new engine runs rough

[4X4fred]

I have a 92 4.0L cherokee with a dead motorL (so much for letting teenage son drive my car and swapped in a 95 4.0L. Anyway, The old engine came ou with the usual problems: too many different size bolts, hard to reach bolts, the list goes on and on but finally got it out.(mind you this is my first engine swap project) Installing the new engine is another story. I believe the recycler sold me a 4.0L from a 95 cherokee if you go by the tag on the front of the valve cover (does anyone know what these number mean). Anyway, to make a long story short, I had to transplant from the old engine to the new the following: motor mounts, alternator mount, fuel rail(but not the injectors) several vacuum fittings on the manifold; fly wheel (the holes on the newer flywheel would not line up with the torgue converter holes--discovered this after installing moter in car); AC mount (holes don't line up). The original moter had 2 fans: one connected to a pulley on the left side between the AC and alternator AND an electric fan on the right. The newer motor..when you connect the fan to the pulley it hits the waterpump pulley. I just mounted on the water pump and left out the electric fan. Once I got everything connected and back in, the engine actually started fairly easy. Problem is that it stalls and hesitates when you give it gas. Discovered a engine to body gound wire that didn;t get connected. Once connected, it runs somewhat better but still get the hesitation and a little backfire when you give it gas; like the timing is off. It has new plugs, wires, distrib cap and rotor. also added another motor to body ground. I am beginning to suspect the crankshaft position sensor. I read this sensor controls engine timing??? Also read something about OBD I vs OBD II type system. One uses a fuel return line and other doesn't. My original engine did, the new one did't, thus swaping out the fuel rail. Next I'll check the fuel pressure but need to buy the tool first.

So, any help on solving this problem would be appreciated.

[gtmud]

Sounds like you might have gotten an HO engine, to swap out your "Standard" 4.0. Did this engine come with the intakes and exhaust manifolds? If so what are the differences. THe HO's didn't have the EGR valve and the t-body is very different.

[4X4fred]

THe shapes between the two were the same (retangular), but some of the vacuum locations like the brake booster manifold were different. Also, the fuel rail on the new motor only had the feed line, no return line. I switched in the old rail which had the feed and return. As for the exhaust manifold, nothing really different.

[gtmud]

what about the t-body? Did you just swap them out? The HO t-body uses an IAC instead of a step motor to control idle.

[4X4fred]

I originally stayed with the t-body on the new motor. I did switch to see if it made any difference. It didn't so I put it back on.

[gtmud]

IT sounds like maybe you have a vacuum leak at the intake. Disconnect the MAnifold air temp sensor, and see if your stumble goes away. If so I would start looking at your intake and exhaust for a vac leak.

[4X4fred]

Originally Posted by gtmud

IT sounds like maybe you have a vacuum leak at the intake. Disconnect the MAnifold air temp sensor, and see if your stumble goes away. If so I would start looking at your intake and exhaust for a vac leak.

After checking everything, and I mean everything and still dealing not able to solve the problem, I took it to a local shop. Needless to say, after three weeks, they couldn't figure it out either. HOWEVER, going back to basics, I found out that the Jeep changed the distibutor for the 94 model year. I had installed the distributor from my 92 moter into the 95 motor. So I purchased a distributor for a 95 4.0, installed it and everything is good.

A lesson learned, during an engine swap, keep the old engine until the new one is running and if swapping different years, check the parts catalog for campatibility.

Thanks for help. Next project, install a 3 inch lift kit. Any words of advice???