Engine/Tranny Vibration

I have recently bought a 2wd '94 cherokee and swaped it to 4wd using the tranny, t-case and axles out of my '89. While at idle, reving, or at speed driving down the road the engine vibrates or seems out of balance( not a severe vibration, but definitely noticeable). The check engine light comes on sometimes also, not sure if this is because the spedo is not connected or because of the vibrations (i'll have yet to get the codes on it).

The vibration looks to be toward the rear of the engine where the flywheel is and meets the tranny. The only things I can think of are the harmonic balancer is messed up because the bolt that attaches it was tightened a bit while trying to allign the tranny, the tranny is not bolted up properly (i don't know how this would be but an idea), or the flywheels on the different engines are balanced differently. I have made sure everything is tight including the flywheel bolts and the thing still vibrates. Anyone have any ideas on the subject?

Thanks.

I think the 4WD has a different tranny mount than the 2WD, you might need to swap that.

Did you use the driveshafts out of the '89 as well?

How is the axle mounted on the spring, compared between the two? If the driveshafts are different length, the angle will be different and U-Joints off angle will produce vibrations.

Do the key on/off 3 times ending with the key on, to get the CEL to blink out the stored fault codes in the PCM. That will tell you why your CEL is on.

I used all the drive line parts from the '89-drive shafts, tranny mount, etc. I have found that the check engine light is due to the speedo cable not being hooked up. The vibration is while I am moving or not, so I don't think it would be the drive shaft. Any thing else?

Motor mounts? tranny mount? I had a slightly loose crossmember and it would vibrate the heck out of the truck and it wasn't very loose and I kept checkingt thatI had all good mounts. Usually when something vibrates its worn out or not tight. Good Luck .