Evening gents,
Ive been noticing a strange vibration in my 08 (xl 2wd, 5.4l, 6.5', 3.73ls) when under heavy acceleration in 1st gear. Almost like a small shudder. Shifts fine into 2, 3 and 4. I don't tow anything regularly and i have stock size wheels and tires. I am lifted 2" front and back. Put a new driveshaft in it because the center support went bad in January and have had a mag-hytec trans-pan on it for a few years. Fluid level is perfect and the color is good.

Should I be concerned about the transmission slipping? Is that what ya'll even think it is? Where should I look next. I tried searching but couldn't find much.
Thanks for the help!

 

You might not have a troubled transmission.

You might be having a low grade misfire.

When was the last time the plugs were changed?

 

Good call! I saw the same thing happen to a few trucks. I changed the plus around 75 or 80k. Im at 145k mi now. I feel like a bonehead. I'll do those and report back. They are due anyways.

 

That is likely the cause.

Make sure you use Motorcraft SP-515 plugs only.

You may want to replace your coils. If you do, make sure you use Motorcraft.

This is critical, don't skimp.

 

No no no - use SP-546, they have replaced SP-515.

Denso and Delphi coils are also acceptable.

 

I keep forgetting, yes, use the SP-546. If you buy them from a reputable online place, even if you type in SP-515, you should get redirected to the SP-546 plugs.

 

I'd also inspect the u-joints.

 

It might be limited slip chatter. When was the last time you changed the diff lube?

 

I changed the diff fluid last fall. Used valvoline syn. The vibration happens on dry pavement going strait so I dont see how the limited slip could be causing the issue.
as far as the u-joints are concerned, they were just replaced when I put in the new driveshaft. And I don't feel the vibration at highway speeds, though it could be masked by the crap roads in va beach.
I did pull $84 data and it showed a misfire...sort of. I'll try and post a pic of the results.

 

is that the plug for the new style heads with the brown boots? If I remember correctly the old style had different plugs?

 

Nope, the plugs for the new style heads are SP-509. The SP-546 is the latest (3rd) revision for the old style heads. They came with SP-507, replaced by SP-515, now SP-546.