1997 jeep grand cherokee backfires while in motion on expressway and had to replace 2 mufflers. what is causeing this backfire.

Three things can cause backfire, excess fuel igniting in the exhaust, air leak in exhaust causing normal waste to ignite or spark plug firing when exhaust valve is open (timing fault or bad ignition cap)
Check for codes, examine exhaust system for leaks ahead of the converter. check cap and rotor for tracking between contacts.
Three things can cause backfire, excess fuel igniting in the exhaust, air leak in exhaust causing normal waste to ignite or spark plug firing when exhaust valve is open (timing fault or bad ignition cap)
Check for codes, examine exhaust system for leaks ahead of the converter. check cap and rotor for tracking between contacts.

My 97 is doing the same thing was told it could be the map sensor since everything else has been replaced. My 97 is doing the same thing was told it could be the map sensor since everything else has been replaced.