My 2010 F-150 4x4 crewcab engine misfires every time I tow my cargo trailer and exceed 3,000 rpm. The first time it misfired It had 115,000 miles on it so the dealer suggested changing the plugs since it did not throw a code. That did not help as it misfired the next time I towed and that time it threw a code that said chamber 5 misfired. So the dealer replaced the coil. The next time I towed same thing and code said chamber 7 misfired so they replaced the coil and plug. Next time I towed same thing and this time it is saying that chamber 3 misfired. At this point I am getting frustrated as every time I tow and exceed 3,000 rpm the engine misfires and throws a code that a different chamber is misfiring. Is this something that is common? Do I just need to keep replacing the coils until it hopefully stops or is something else going on? The truck tows perfectly fine under 3,000 rpm and the trailer is well under the towing limits. Any suggestions?

Another issue is when I drive (not towing anything) at about 30 to 35 mph and the rpms are at 1,000 the truck lunges back and forth. It doesn't do this at any other time just at those settings. Don't know if it is related or an entirely separate problem. Any help would be appreciated as dealer has not been able to identify.

 

Engine?

Rather than playing 20 questions ...

HINT/TIP: Put your -complete- vehicle information (year, model, cab, trim, engine, wheelbase, _x4 drive, mileage, modifications, etc., etc.) in your signature -OR- provide it in your posting(s).
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2010 Ford F-150
Crewcab
Lariat
5.4 liter V-8
66" bed length
4 x 4 automatic
118,000 miles
No modifications

 

Does this have a changeable fuel filter?

 

No. *Since 2009 ... Your vehicle is equipped with a lifetime fuel filter that is integrated with the fuel tank. Regular maintenance or replacement is not needed.
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Given the miles and since maintenance isn't mentioned, would recommend ...
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I am betting the coils are fine but they didn't change the coil boots and you are getting carbon tracking in the plug wells and loaded misfiring.

 

This was my first thought too. At that mileage, the coils could be going bad, too, but I'd try boots first. Also, what brand plugs are you using? the 5.4 is pretty picky when it comes to OEM Motorcraft plugs.