I have a 91 Cherokee 4.0 straight 6 the other night I drove through some deep water it didn't bog down are shut off or nothing it did just fine but the day after I started it up and noticed a loud knocking coming from underneath it goes away when I accelerate but then cones back any ideas

 

Flexplate would be the first guess by your description. They are prone to cracking around the bolts that hold it to the crank. Those cranks soon spread and will completely seperate the flexplate into 2 pieces. It will usually have enough of an odd pattern that it will continue to make contact against itself and allow the vehicle to drive. When idling in park or at a stop light it will make a knocking that sounds like the motor is about to blow up. When under a load like acceleration, then pieces have enough pressure on them to stop the knocking.

Remove the inspection cover on the bottom of the bell housing and check the flexplate for cracks. Also check the 4 bolts that hold the flexplate to the torque convertor as they like to back out over time and make contact with the trans housing and cause a similar knock.

 

Here is what the flexplate looked like in my 91 after I pulled the trans out to replace it.

$130 for a transmission jack
$15 for a flexplate at the junkyard
8 hours of profanity in the driveway
All add up to no more knocking.

 

Thanks......I did that about an hour ago I didn't notice any cracks and the bolts I did see were tight how do I get to the other two and what would u think if its not that problem