i have a 91 cherokee and my buddy has a 97 cherokee. we are both having trouble with them back firing thru the throttle body. it happenes worse in high. it still does it in low but not as bad. any ideas on what our problem is

 

Backfiring is generally caused by a fuel/air imbalance. Usually lean if the backfire is in the intake. Any check engine lights/codes?

Start with verifying fuel pressure. You can rent a fuel pressure gauge inexpensively from many parts stores; call around.

For the 91, you should have 31 psi at idle, then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be sure that the vacuum line is pulling good vacuum and is NOT wet with fuel (which would indicate a ruptured fuel pressure regulator).

For the 97, you should have 49 psi, plus or minus 5 psi.