6 speed auto, 4.6L Screw. I get that same shuddering/noise that you get when driving on highway "rumble strips". I only thought it was doing it around 45mph, but last weekend I had to drive to Houston and back (about 400 miles round trip) so I got a good chance to test it. Here's the info I've come up with during this "test" drive:

Happens frequently at about the 45mph and 65mph range. Approx about 70% of the time. I also noticed it happening while decelerating (without the brake), such as going uphill. Once I accelerate past the range, the shuddering stops.

RPM's DID NOT seem to be affected. I made sure to check my RPM's when this was happening, and I noticed that the RPM's were steady during this noise/shuddering.

The issue happened with or without the "TOW/HAUL" off. This didn't make a difference at all. I don't think TOW/HAUL affects RPM's at higher speeds anyhow.

To add a little drama....a lady at the giant gas station backed into me as she pulled out and I was in the parking lot lane. She ripped a hole my BFG's sidewall, so I put a spare on...that was a slightly smaller size. I had about 100 miles to go, and it seems like it did it nearly constantly after the spare was on. It seems to have gotten much worse after that. Whether this was from the smaller tire or because I was now 6 hours into the trip and it was warmed up, I'm not certain.

So because of the smaller tire, I get the ABS brake light and the "swerve" led light in the display which is normal when having a different sized tire on. Truck ran and braked fine though. The reason I include this info is that it seems to have gotten much more pronounced after this.

I did the driveshaft "bump" fix a few years ago where you add the lubricant in the slipyoke and has been fine for at least 4 years, so I don't think it's related. I was worried about a tranny shudder, but since RPM's seem to be steady, I don't think that's the case any longer. Could this be a driveshaft or ujoint issue? Any help is appreciated.

 

Usually a misfire from weak coils. Change the plugs first.

 

Thanks Roadie. Definitely something that's overdue. I will check that out.

 

Just wanted to update this.

Replaced all 8 ignition coils first. No dice. Actually made the problem worse.

Replaced all spark plugs and the shudder is gone. All 8 came out fine, no breakage.

 

As expected. The 2 piece plug design on the 3 valve engines was not used after mid-2008.

You may want to put the factory coils back in. If you replaced them with aftermarket, they are not as good as what you took out.

 

Turns out I spoke too soon. I took the truck on a road trip up to the Ozarks...about 7 hour drive....happy as a pig in you know what...thinking I fixed it.

Well, not 20 miles down the road and it came back. I seemed to be different though. Not quite as bad...a little smoother. But I could tell it was a bit different. Still annoying as hell but different.

I was hoping that it would clear itself up, but it was intermittent the whole time. Sometimes it would be fine for an hour then shudder. Mostly going up hills....and oh man are there hills everywhere up there. Which is why I wanted this fixed before I went. Sometimes going up hills was perfectly fine though. So, very intermittent.

I just got home and back to square one. I think I will put the old COP's back in. I saved them all. Being cheap $80 a set coils, I'm sure they're crap. I couldn't get the Motorcraft ones here on time so I just got those.

Anyhow, thanks for the advice and I shall report back in a couple days.

 

Throw some Techron in the gas.

The only coils I trust are Motorcraft, Denso, or Delphi.

 

Update:

Put all the old original coils/boots back on and same issue.

So, to summarize - 8 new Motorcraft plugs and original coils/boots. Same issue occurring.

It's possible there's still a coil that's bad. I'm going to ohm them out and clean them all up and see what that does.

Since I get no CEL codes, I may get a Bluetooth OBDii and Torque app to monitor misfires so narrow it down if it doesn't get better.

I really don't want to dish out 250 bucks for all new Motorcraft coils at the moment. I would if I knew that would take care of it, but I'm starting to wonder if I'm barking up the wrong tree at this point.

 

Update

Got a wifi OBDii reader and used OBD Fusion app with the $06 monitoring. Drove around a few miles and got it to shudder many times.

Looked at the data and all 8 cylinders show 0 ZERO. All sensors monitors show Pass (within specs), but there were a few gas sensors that show some values...though they are in limits. I also got a value on $A1 MISFIRE MONITOR GENERAL DATA as below

$A1 MISFIRE MONITOR GENERAL DATA
TID $84 - Manufacturer Defined
Minimum -40 Maximum 1288.04 Value 890.6

So on VALUE I got the 890.6 instead of 0 I don't know what that means, and I'm having a hard time finding anything. Obviously it's within the specs but still could indicate something. I also get some values on Exhaust Gas Sensor. While within specs....they still show some values.


If anyone can makes sense of that, I'd appreciate it. I can't imagine a weak/bad Oxy sensor would cause a vibration 45-65 @1500 rpm. Idle seems fine.

So, I may start looking at the ujoints next, even though I really feel this is a misfire issue.

 

When a u-joint went out on my 94 F150 4x4, it shook on decel as I remember.

 

Yeah, I've had them go out in other vehicles and this doesn't seem like that...but I'm just trying to think of everything.

Like I said in the very first post...I remember it getting much worse when I had a smaller spare on the rear passenger side for a 100 miles or so. This is the only weird thing. I don't think a smaller spare would cause worse misfires...but I don't know. There doesn't seem to be any play in the ujoints even though they are rusted up.

I bought the truck at 80k and it now has 160k. I've never done them so they're probably due anyhow.

 

If you have limited slip, different tire sizes can cause clutch chatter.

 

Update.

Well, I was at a loss so I put in that tiny 2oz tube of Dr Tranny's Instant Shudder Fix. I've had it for a few weeks but just assumed it wasn't the tranny so I didn't bother.

Put it in and I be danged the shuddering is gone. So, I suppose it was the Torque converter locking up. Also, the truck shifts like butter now. I didn't realize how bad it shifted until now. Even my daughter said something about it when I was taking her to school.

So, looks like I'll need to do a ATF fluid change soon. I'm at 160k (bought at 80k) and I've never done it. I'm one of those people that believed Ford that these trucks are maintenance free. I just wish these had a drain plug.

Not sure how long this Instant Shudder Fixx will last, but I don't want to push it. I'll update if anything else pops up that may help someone in the future.

 

I'd recommend you take it to a shop that has an exchange machine to do the transmission fluid change, and it takes Mercon LV fluid, not universal.