I have a 2006 Lincoln Mark LT with 123,000 miles, Every time I go about 45-48 miles an hour the truck makes a bucking sound.

 

nobody has any idea why my truck starts to buck when going around 40-50 miles and hour?

 

Makes or you feel a bucking. Do you do a lot of driving in that speed range? If so, your TPS may have developed a "DEAD" spot causing the issue. Since the TPS is a variable resistor, the "DEAD" spot will be 0 resistance telling the computer not to inject fuel as it passes over that spot causing the buck. You can check with a DVM. Should have resistance reading thru its entire travel range.

 

At that mileage, possibly ignition breakdown related as well. Any history of related parts being replaced?, would be overdue 123k

 

Makes and you can feel a bucking, no I don't do a lot of driving at the range, I don't now what DVM stands for sorry.

 

Not that I know of, bought the truck with 98,000 miles, the only thing I changed was the spark plugs.

 

No worries...DVM = Digital Volt Meter. You can also use a "Needle Swinger" (A.K.A. Analog Volt Meter).

 

Dang, I should have known that, I did change the coil packs on Saturday and it wasn't a bad job at all, about 1-1/2 hours, Now I'm still going to change the TPS, Is it a good idea to change all the sensors or should you change them after so many miles?

 

So,, coils had no affect on the issue?
Generally if have an ignition breakdown, random or continuous , or a TPS drop out, the CEL will set. Not always, or may illuminate and go out ( more so TPS) but you make no mention of it. If the misfire counts exceed, the CEL will set...
123k isn’t high mileage, and most of the engine management parts are changed as needed, not at intervals...

 

Thanks, When I took the truck for a test drive for about 1/2 hour after changing the coil packs it didn't do it at all which is a plus, I'm not so sure it is a misfire or it would do it all the time wouldn't it? But I wanted to start somewhere, the truck didn't do it all the time before just occasionally at the same speed but did seem to do it more, so I thought possibly a weak coil pack but want to change the TPS too so it will also eliminate that also, Sorry I must have misunderstood your earlier post when you mention parts were over due at 123,000 miles.