Lately I have been loosing power in 4th gear. I'm fine in 1, 2, and 3, but when I get into 4th I have no acceleration. It is most visible when I am accelerating from 30-60mph. It also seems to shake pretty hard when in 4th. Any ideas?

 

I don't know which engine you have, but that was my biggest complaint of the 4.6 and why I eventually traded. Once my 4.6 got into 4th it was "game over player one". Never experienced a shake though. Where does the shake seem to originate ?

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99 F150 5.4 4x4 ORP 3.73 styleside deep wedgewood blue ..no mods (yet)

 

strange: when's the last time you did a tune-up??? Check out your plugs. Also, could it be out of alignment?? How are your tires??

 

I know it's not the tires, I've been told it could be the plugs also from other people. I was checking for other opinions here. I replaced the plugs and wires in 1997 - is it time for a change?

 

it wouldn't hurt to change them and well thats more of a miles thing than a time thing. So if you put alot of miles on it in a year you should have a tune up done every 30,000 miles unless you have a more modern truck that they say can go 100,000 miles befor a tune up but I would change them long before that to avoid trouble.

 

Sorry for lack of detail. It's a 85 F150 I6 4.9L. I guess it's just when I'm in 4th the engine really "lugs". The weird thing is that it doesn't happen all the time. It takes me about 1 minute to get from 30mph to 55mph, and once I get there it sounds like the engine is running really hard. Hope this helps.