Truck Details:
2008 F150 4x4
5.4 V8
3.373 LS
52k miles
Stock 20" wheels
Edge programmer running #2 - Towing program

I am experiencing a shudder in the rear/drive train when accelerating in 4th gear.. It happens under moderate acceleration when the torque converter unlocks, for example when going up an incline. It feels like hitting rumble strip on the side of the road, but only on the rear tires. I have not been able to duplicate it in 3rd gear. My Edge programmer is set to display the trans gear and shows when the torque converter locks and unlocks.

As some additional info, I have just replaced a cracked manifold on the passenger side> I replaced all 8 spark plugs.

Is this a known problem or complex to solve?

 

Sounds like a moderate misfire.

What plugs did you use when you replaced all the plugs?

 

What happens if you remove the tune and put it back to stock?

 

I don't know, I had it done at a local trusted repair shop. I am thinking of bringing it back go them before I take it to a trans shop.
The invoice just says: Spark Plugs (IRIDIUM)

 

I was thinking of trying that first. I'll have to wait until next week. My son is flying in to town and he'll drive the truck for a few days.
Putting it back to the stock program seems wise at this time. That way I don't have to fear some shop reprogramming it to solve the issue.

 

I would've had them put in Motorcraft plugs.

 

If they put iridium plugs in it, you have a late 2008 with the revised heads (engine build date after 10/9/2007, sticker on the cam cover), there are 3 brands available - Champion, NGK, and Bosch. If yours aren't NGK, they are suspect. The best plugs are Motorcraft double platinums, SP509.

The old head design has no iridiums available, they take Motorcraft SP546 platinums.

 

I've seen this before. Changing the transmission fluid has fixed it.

 

What Mark says worked for me when my 05 did the same thing. Trans was hot after a three hour drive at interstate speed in July, same issues except mine also shook at take off at the top of the off ramp. I just locked out overdrive to get me the last five miles to my house. At that time I changed all fluids, fuel filter and replaced sparkplugs with OEM - still had an issue so I took it to a trans shop and they recommended a pan drop / oil change on the transmission before they tore into it. So far it has worked fine.

 

Note that a pan drop only gets about 1/3 of the fluid out. The right way to do it is with an exchange machine.

 

Yes, the engine build date was 10/30/07.

 

Sounds like a plan. Do I need to bring my own fluid? Find some Amsoil?

 

Thanks for the confidence.

 

Ask the shops what they use for fluid. Any fluid that meets Mercon V specs should be fine. Don't use Mercon, Mercon LV, or Dexron anything. Don't use any additives.

 

Thanks.