06_F150

If all else fails don't dismiss tire balance. I had a bad balance once from the get go. Either it was a mistake or I dropped a weight. One thing you can do is accelerate past the speed and put it in neutral so the engine rpms drop and see if it still occurs when you coast through the problem speed

CSprain

I don't think it will because if I am at 55mph and it is shaking, as soon as I let off the throttle it stops shaking. It is only under throttle. I did think it is possible that the shop messed up the balance.

bourgeois1269

I guarantee you it's the tires, I have Kanati mud hogs and had them balanced by 2 different shops and the second shop had to add atleast 30oz of weight to balance my front. The back end of my truck would shake so bad until I let off the gas

CSprain

I have another set of tires and rims so I guess I will swap them out and see if it goes away or not. Then I will let you guys know. If anyone has more ideas let me know.

rfinger

Mine is doing the exact same thing. My question is this though everyone is stating its the tires but if its doing it at idle as well how could that be the tires?

primalurges

well I believe it was described as rough idle and really bad vibrations at 45 mph. A lot of 5.4s have pretty crappy idle. Tires are the cause of most vibrations especially in the 45 to 55 range so it's just something that can easily be ruled out without throwing parts at the problem.

rfinger

gotcha....i was like ummmm not all questions are being answered and it seems like a blanket statement even though that would have nothing to do with the idle

CSprain

I was going to take it one problem at a time yet. I have two do the 04 to 08 trucks. The project one idles a lot rougher than the other one. To the point I am pretty sure something is wrong. But if I can solve one problem I would be happy then move onto the next.

CSprain

Well I found the issue. Cylinders two and four are misfiring. What is the best way to tell if a coil is bad?
This is probably the cause of the rough idle as well as the shake at 45mph.
I did not replace the boots on the coils when I did plugs. I wanted to test the coils before I replace the boots now. Thanks for any help.

TexasKid747

This is almost rhetorical, unless someone has the answer. lol.

I can't image two coils at once with the problem, one was bad enough. Not enough to make me quit driving it, but enough to make me concerned something serious (and expensive) was wrong.

Why is it that the bad Coils aren't tripping a code? I got lucky measuring the resistance at the primary on only three coils from the engine, and one new one in the store. (1.0 ohm on 200 ohm scale is a good reading - 2003 5.4L SCREW. The bad coil measured 3.5 ohms)

Now that I have that knowledge and experience, it seems easy.