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2005 freestar 3.9 backfire

This van has 200000 miles. When I give it to much gas(about 2000rpms on the tact)it make a popping sound,almost like it backfiring.Its has new plugs and wires and map sensor. It anyone has had this problem, please let me know what will fix it? Thanks

At 200000 miles it is time to have your timing chain checked. Both engines, the 4.2 and the 3.9 have timing chains. It’s possible you have another problem but I’m making the most obvious diagnosis at this point. Timing chains slip a notch or two but they seldom break.

I had 2 different garages look at it and one told me it was the 02 sensors and the other garage told me it was a leak on the intake manifold. Any thought?