Well my truck backfires when it gets up to 60 to 70 mph only than after that it keeps backfiring and losing power (but not when the engine cooled ) when the engine heats up , I replaced the spark plugs, (spark plugs turning white and the spark don't like they 're burning gas )and wires thinking it was that than took off the muffler thinking it was that(before that the muffler was having white smoke with water , that's the far as I got
My car has an automatic transmission.
Hello, your description of having "white smoke with water" out the exhaust pipe strongly suggests a blown head gasket. This can cause a misfire depending on how the head gasket has failed, this will definitely cause loss of power and the "steam" you notice. You are likely seeing overheating and possibly a Check Engine Light illuminated as well.
I would recommend having a misfire inspection completed by a mobile, professional mechanic, such as one from YourMechanic, to diagnose this problem, get an accurate assessment of damage and cost estimate for repairs.
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