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3.9 ford 2005 backfire

At 2000rpms the motor backfires. It has new plug and wires and map sensor. 203000 miles

Backfiring usually means it is getting gas or too much gas at a place or time when it shouldn’t be getting any or that much gas. Often times this is related to a timing issue. I’d start with a good look at the ignition system, wires, dist, etc. Check the timing. Could something be leaking? Is the advance working (if it has one, it’s probably electronic.)

I’m curious, what year/s did Ford make a 3.9 engine?? It saeems to me that the original V6 was 3.9.
No, the original one was 2.9 sorry.