I recently purchased a 2009 F150 Lariat, 4x4 (5.4L V8). I bought it with 94+ K miles on it, and the test drive was fine, uneventful. I requested the plugs be changed out before delivery, since it was so close to the first tune-up mileage.

When I drove off the lot, I noticed a feeling like a slip, or jolt in the driving of the truck. At first it seemed to be more focused around highway cruising speeds, but after dealing with this a few weeks, I find it most pronounced when the engine is cold and accelerating early morning, or when driving up hill under loads (1500 lbs in the back). After being on the road awhile, I can still feel the problem while cruising, but definitely find it increased under loads or while the engine is cold.

I returned to the dealer with the problem. At first they said the truck was fine, and tried to send me on my way. I insisted on a road test. The service manager went on the road with me, felt what I was feeling, so we pulled over, and he drove awhile. He felt it also, and decided to clean the throttle body. Problem persisted.

I returned to the dealer, and the warranty manager then drove the truck with me. He said it must be my tires. They are large - Toyo, 35" I think, maybe a bit big for the truck, but I am pretty sure I've driven a lot of trucks, and several of them Ford, as I'm a farmer, and a search and rescue K9 handler... plenty of off road and truck driving. He finally decided it was the cat converter locking down, and made more noticeable by the tire size.

I call BS. In reviewing other forums, I question the plugs or coils. That is fairly logical given the change of plugs pre-delivery. On a longer road trip, the slip or jolt was quite severe.

#1 the truck is not driving smoothly.
#2 the truck did not do this during the test drive.

I'm looking for some thoughts on what to check for. I'm taking the truck to a non-dealer mechanic, and we'll first do a road test.

Also looking for any recommendations of fine Ford Master Mechanics in the Spokane WA area.

 

sure they changed the plugs? my 2009 acted up and shifts seem to drag, replaced plugs myself and drove like new. Pull battery cables and clean posts, take positive to truck to ground to bleed any stored voltage. 09 and up have adaptive learning transmission, this will put it back to factory default. I do this about every 6 months for ****s and grins. worth a try. I would pull at least one plug and inspect to make sure they actually changed them. Gap seems to be critical on our engines. I don't trust dealers but that is just me.

 

Thanks for the tip - no I had my doubts that they actually changed the plugs (which I paid $400 for). And I'm pretty offended they'd say the truck is running as it should because it certainly is not. I'll try the battery trick. I'm taking it to a new mechanic not affilliated with the dealership, but was hoping to find a Ford Master Mechanic, or one who likes Fords. The other mechanic I have recommended to me does not like Ford, lol

 

Note: I notice the jolt is rhythmic at cruising speeds. I can count about 2-3 seconds rhythmically between each bump.

 

Why did you pay 400$ to change plugs??? Seems excessively high

 

the driveshaft can cause this bump also. If you remove the driveshaft and boot and grease the spins on the shaft of may help also. There's a tsb to grease them!