2003 5.4 F-150 4x4 V-8 L with 4R70 auto transmission
285/70/17


So real quick question... when I'm driving down the road in high gear sometimes around 50mph my truck will "act" like the peddle is let off for like 1 second by itself. It happens so fast it's almost not noticeable, but of course I notice it. What could this be? I'm going to do a full tune up soon including the spark plugs, coil packs, fuel injectors, fuel filter, throttle body sensor, transmission fluid change and filter only. Not a flush unless I read different on here. And a new belt. I'm thinking of changing the differential gear oil too. But not sure if I should. I plan on driving to Alaska from the East coast in a few months and want it in tip top shape. And I'm doing everything I can think of to save gas. I did the Gotts mod and new muffler on it and getting a tuner. I really want to see if it's possible to change my 4 speed to a transmission with a extra gear. (6speed) Is that even possible? Any advise would be VERY appreciated.

 

If it feels like it bumps under slight acceleration it's a misfire

I wouldn't replace the factory coils unless you had an issue specifically with them.


They make stand alone controllers for the 6R80E but I don't know of anyone that has attempted that swap by itself yet. Especially on a 4wd truck

 

I'd change the entire PCV system, hose valve and all. The 5.4 is noted for these being an issue and considering yours is a 2003, it's over due if it hasn't been changed. The rear axle fluid and front axle fluid is supposed to be changed every 35,000 miles IF it has the T-Lok axles. You may have a T-Lok on the rear only or you may not have one at all. You'll find the axle code on the door frame to find out if you do or not. The axle fluid requires a friction modifier which is alcohol based and is hydroscopic, for the T-Lok axles only. An open axle does not need the modifier. If the transmission fluid hasn't been changed or you don't know when it was changes last, I suggest a flush using a high mileage fluid to get the extra seal swell agents for the seals.

 

On your trip you are going to be in overdrive most of the time. And with your 2 sizes oversize tires, it will be geared as high as the engine will pull it. The 6 speed wouldn't help on the highway.

 

Makes sense I guess. So your saying the truck is going to be working in (high gear) the gear low enough to be pulling the tires and truck. Just seems like extra gear would pull my RPM's down a little to reserve fuel. It turns about 2k or a little more going around 80.

 

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It says "B6"
I will definitely replace the axle fluid and trans flush like u said and replace the PVC system.

 

I guess I'll check each coil? I thought it would be wise to replace them all with new motor craft coils or what ever is better.

 

I wonder if I can change the gears in the rear end to make the truck better on gas?

 

B6 is 3.73 limited slip. Changing the gears will not help with gas mileage - even if it did, I doubt the gears would pay for themselves before the truck dies. If you get over 15 mpg on the highway, be happy.

 

6th gear in the 6 speed is almost exactly the same ratio as 4th gear in the 4R70W. In fact the 4th gear in the 4R70w is slightly higher geared. The 6 speed has a much lower 1st gear and 2nd gear, etc. If you could put a 6 speed in your truck, it would be much faster off the line.

I did some more research and found at least 3 different ratios supposedly for the 4R70W. So, I don't know what it is but it's still close enough to the 6 speed that the highway gearing would be close to the same.

 

I don't see the rational of changing a transmission for gas mileage when the total cost of the conversion will be way more than any savings in gas plus all the other intended expenses.
The computer is not capable of controlling 6 speeds.
At 2000 rpm cruise, you don't want to run the motor slower because it does not have enough torque to pull the truck's weight of about 5500 pounds depending on what else you have in the truck.
If you have a 3:73, the OD ratio is .77.
3:73 TIMES .77 = 2.87 rounded off for final; drive ratio.
If you get lower in gear ratio the motor is not turning enough RPM to make enough torque and will down shift even more consuming the gas you think you will save.

Leave things alone otherwise do the Belt, coolant hoses, fluids, brakes etc.
The studder you have in OD is a faulty coil.
You may change all 8 coils or use a Scanner to find the faulty one, otherwise take a spare coil along.
You seem to want to spend a lot of dollars to save pennies.
Your best bet is to know the truck mechanically, have tools and some common parts that could fail and leave the rest to fate or whatever happens like everyone else has to take a chance on for a trip like that like what would you do if a fuel pump failed?
Good luck..

 

Your right. I'll just do basic preventive maintenance and leave the rest to do if something happens. I appreciate all of your replys!!!

 

Years ago, my folks went to Alaska in a 77' f250 back in the early 80's, with a slide in camper in the bed. & did everything, as far as , "preventive maintenance " much like you are doing, which is very good!! Dad even took oil and filters along to change along the way. If I recall correctly he put on about 8800 miles that trip, so he changed oil & filters twice! He just disposed of the oil at truck stops or waited til they got back. So if your coming from the east coast...you could feasibly nearly double the amount miles. Depending how far you get into Alaska.

The next biggest/best thing that they did that saved them from on the road costly repairs was a spring loaded net like thing that extended about 10-12 inches above the hood and full width of the truck. It was mounted in front of the grill so it helped to protect the headlights and radiator and windshield. If you get off the beaten trail a bit you will be happy that you have it. Dad said that without it, they probably would have needed to replace at least 2 or 3 radiators and windshields. The road rock is not small up there, (at that time anyway & 2-3" rock was small), and the on-coming Semi's would scatter and throw the rocks everywhere. Maybe a good grill guard or heavy bumper combo will maybe do it today? Also a good set of mud flaps.

Are you pulling a camper?

 

The Alaska Highway is now fully paved so the rock issue is a lot less than it used to be.

 

Oh I'm sure that it is...a heavy duty bumper and grill guard still could not hurt....the moose and elk and whatever else that might wander out in front of you can still really make a mess. The spring loaded net still might not be a bad thought , as it helped keep the bugs off the windshield too....and if the OP gets off the beaten trail, those roads probably will still have similar road rock.