Hi, is it possible to install a block heater (frost plug type) in a 93 4.0L without removing anything? I did some google but cant find any good writeup or pictures/video about installing one.

 

You just need to drain the coolant and remove one of the freeze plugs. The block heater installs in the hole where the freeze plug was removed.
On here if you click the small icon it shows installation instructions for the V-6 but it's similar for the 4.0L>->http://www.jeepworld.com/accessories...gineheater.htm

 

yes, i know that. But is it possible to remove one of the freeze plug and install a block heater without removing anything else in the engine?

 

That depends on your mechanical skills. You shouldn't have to remove anything that's attached to the engine, but the room might be limited under there.
Here's a diagram of the 4.0 L engine because I can't find a real picture that shows it very good. (Ignore the sensor notation)