Hello all,

I have a 2005 Lariot 5.7 litre. This issue has been going on for a while but is becoming worse/more consistent, to the point where i can make it happen at any time while driving. The issue is, between the speeds of 40-50mph, if i accelerate, the truck will speed up but it makes a jerking/bumpy feeling. Almost like it is trying to shift gears but it can't. Given that info, if i go to accelerate in that speed range and this issue occurs, i can step on the gas hard, it will downshift and speed up quickly without the herky jerky motion. But if i try to lightly accelerate, it is a very bumpy/jerky ride until i get to just over 50mph.

I have been told a few opinions from different people who have had these trucks. One being my transmission could be going bad. The other being the spark plugs could be shot and need replacing (which i hear is a very long and pricey job on this engine).

Anyways, if anyone has thoughts, ideas, whatever, much appreciated to hear them before taking it in to a shop.

Thanks,
Jeff

 

Spark Plugs. VERY common. How many miles you have on it? Cheap (ish) if you do yourself. Search on this forum for how to or youtube "5.4 3v spark plugs." FordTechMakuloco youtube channel will be your best friend.

 

Could also be a COP.

 

Thank you, I will check out that channel.

 

I had similar symptoms this spring.

What I did:

• Dropped the transmission pan
• Installed new filter
• Replaced 5 qts fresh Mercon V fluid

Problem disappeared. Of course I already had new plugs/boots/springs the year before and no misfires.

 

Its always bad spark plugs that cause that jerkiness/bucking on light acceleration at 40-50MPH. It tends to be confused as a transmission problem.

 

You have classic misfire symptoms . Change the plugs and boots-- do a hospital clean job . use a small amount of dielectric grease on boot ends only . Contact spray the cop connectors and clean the high volt tab real well .How many miles on this bear . Plugs are now supposed to be changed out every 60k . If these are orig plugs have lisle plug extractor on hand first . Read the ford bulletin on these plugs . Soak plug base with carb cleaner overnight if you can . Of course blow out area with air gun first . The carb cleaner tries to work past threads and dissolve carbon holding plug tip Ford recommends turning plug an 1/8 th of a turn back and forth to help it flow.Then try 1/4 back and forth after a while . it won't harm the cyl in fact a lot of guys try to remove that carbon with carb cleaner with plugs out as it can break plugs going in . Don't mess with trans until your plug circuit first class. Don't cheap out use new boots on plugs. The new plug is the sp546 ,you won't have this problem with them .
Oil ,antifreeze,age/heat destroy boots it only takes a pin hole .Too many guys replaced trans for this problem and it was the plugs .

 

I never sprayed any carb cleaner before removing the plugs. Just ran a bottle of Seafoam in the tank before doing them. Then the day of, ran the engine for maybe 15-20 minutes till it got to operating temp (middle of temp gauge), then let it sit for 10 minutes before getting at it. Didn't break a single plug doing that, either.

 

Thanks for all the comments so far. This rig has 106k miles on it, and the plugs have never been changed as far as i'm aware. I'm hoping the plugs are the issue as you all suggest. I am not mechanically inclined enough or have enough time to mess with it myself, so i'll be looking for a shop to do this for me.

 

I understand, aint nothing wrong with that. Make sure they use the Motorcraft sp546 plugs. They should but doesn't hurt to reiterate that to them.