I have a jeep grand cherokee with a straight 6 4.0 H.O. Engine with approx 222000 miles, when it is cold out in the morning my jeep backfires after it getting over 2000 rpms, now I have replaced the fuel and air filter, the front pcv valve, the distributor cap and wires and plugs. My father says I have to much oxygen coming out with my exhaust because of amount of exhaust coming out.
If you are losing too much air with the exhaust then that is not good for your jeep. It takes away horsepower from your engine. Why don't you give the exhaust system an overhaul by purchasing a complete jeep exhaust kit specially made for the Cherokee. The exhaust should be proportional to the jeep's engine so that you dont lose a lot of power in the exhaust gases.