In need of help before dropping 1000s, I have a 04 f150 stx 4.6 supercrew AOD. Lift and 19'' 33x12's ..its lacking severely in power after you get to 50mph. Up until that it has plenty of torque drives great but once you get over 50 like tring to hold 70 on the interstate it has to constantly drop out of overdrive into 3rd. I have no rpm gauge but I'd guess it's 3800 to 4000+rpms all the way up to 70 then i have to slowly back off untill it goes into overdrive and repeat..heaven help if there's a slight uphill grade then it starts losing speed fast. Also when im holding speed on level it shudders a little nothing bone shaking just noticeable..first i was told it was the cats, plugs and coils. The intake gasket, plugs and coils and radiator where replaced about 300 miles ago. The cats test ok.the only codes i got where misfire #3 before I replaced plugs and coils. None since. The gearing is 3:73. Is my daily driver so any help would get you kinds of gratitude thanks in advance.

 

personally just sounds like you're asking a lot from that little 4.6

a change of rear gears would help acceleration and keep rpm up so it doesn't have to downshift in OD.

shudder I have no idea - do you think its motor or suspension? Bumping it in and out of OD would help ascertain an RPM related vibration

could always read rpm using a blue tooth adapter and an app or a handheld etc...

 

The "shuddering" sure sounds like misfiring to me. Did that go away after replacing the plugs? If not then I suspect you still have a misfire that's hurting power.

 

You’re just going to have a love affair with that O/D OFF button on the shifter.

The 4.6 really doesn’t start waking up in a stock truck until right about 3800 RPMs. You’re going to need every bit of that to push around heavier wheels and tires now.

 

but that would just be addressing the symptom not the problem..the shuddering may be a miss its definitely drivetrain related. I plan on replacing the plugs and coil packs. Ive owned many cars,trucks over the yrs, with slipping transmissions worn rings/ cylinders and so on but ive never experienced this its like the gearing is double what it should be in 4th/OD..its like pulling a house in hight gear. I noticed when it snowed the other day I put it in 4wd and the back wheels would spin for a second or 2 before the front would engage.no clue if that has anything to do with it....what if someone replaced the transmission with a 4R75w instead of the 4R70E it came with?.. And the 33's wouldn't add THAT much to the topend gearing would it? .....just thinking out loud.

 

If you still have the original coil pack, dont replace them. just replace the rubber boots and the plugs. The original coils rarely fail, but the rubber boots break down and the springs can get crud on them. so just cleaning and replacing the boots usually does the trick and you can do all 8 for the price of one new motorcraft coil.
Also, don't buy the plugs from ebay or amazon there are too many fakes out there. get them from a local supplier or known reputable online source.

 

if you get some kind of a scan tool you could see the engine rpms, with that info + mph (Id take it from a GPS source), your rear gear ration + tire size (I'd get it from the tire manufacturer's site) you can calculate the transmission gearing and verify.

I need to check forscan and see if it will show you the misfire counter or not, I know you can't change much for programming on older trucks with it but still might be a good diagnostic tool.

 

When was the last time you read the DTCs? Autozone and others will read your codes for free.
As others have said shudder (feels like a trans problem but generally isn't) is generally a ignition problem like a coil or plug but it can also be injector related. Every so often it is a good idea to clean the Mass Air Flow sensor its an important input to the computer.

 

From the orange clip to the blue
I have a obd2 scanner but it doesn't give me live data just checks maf,egr, o2, and cats with an op normal..runs great till 65 hits OD and it's like pulling a house.. it loses speed the whole time in OD...Also could the fuel pressure be dropping when the RPM's do? What would cause that to happen hypothetically?.
subject I've seen this in 3 other threads with no answer,people looking for the same thing with no anwsers... in the pic i broke the orange socket side and the clip won't stay..i can't find the fuel line from the blue clip to the orange ANYWHERE.no store nor website, but I walked a local junkyard and found one. looked like itd been hit by a train but it was there. Found a guy that worked there showed him we walked to office .and the brains of the operation told me it was to much of a hassle to take the fuel line off for 6in..i explained 3 times its just the small line from pump to filter. After a few seconds he replied I wanna get it running before we part it out😲😲😲. I've searched and still nothing.

 

I use Torque Pro for OBD. It shows live data although I don't remember if it will show misfires.

Dorman has a fuel line repair kit
https://www.oreillyauto.com/shop/b/f...004-ford-f-150