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Scott W.
Scott W., Ford Technician
Category: Ford
Satisfied Customers: 3322
Experience:  28 yrs. experience as Ford ASE Master Technician. Accolades include being a 2005 Ford PTS Regional Finalist and 2006 ASE Ford National Technician.
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2005 f150: 4wd..50 mph..if you accelerate the problem goes..000 miles

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i have a 2005 f150 4wd that tends to jerk or quickly hesitate when driving between 40 and 50 mph only while on a very slight uphill grade while maintaining speed. if you accelerate the problem goes away. the truck has 122,000 miles on it. I took it into a mechanic who said that he thought it was a spark plug issue due to the miles and not the tranny. He mentioned that this year of truck has 3 piece spark plugs that wear out and cause intermittance. He wants approximately $500 to change out the plugs due to them often breaking during removal. He said that he didn't feel it was the tranny. 4 weeks back I brought the truck in to him for a tranny flush. the fluid was black. he determined that it needed to be flushed twice and did so. I did notice the jerking problem before i brought the truck in to have it flushed however it seems to have gotton slightly worse over time. Is this an ignition problem or drive train problem?
Hello my name isXXXXX this does sound like a spark plug or coil on plug misfire, we use a oscilloscope to test the ignition and replace spark plugs or coils as needed, any more questions just ask, Thanks Steve W
Customer: replied 5 years ago.

Does it concern you that this does not happen at other ranges of MPH?

Not really, a engine misfire will usually start happening under light tip in load like 40-50 mph in overdrive. When floored the mixture goes more richer and it takes less electricity to fire the plugs.
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