I recently got my hands on an 08 5.4 lariat, I drove it home just fine, then out it started losing power, I mean throttle to the floor would barely get it off the line. I've changed all plugs, new fuel filter, which looked like it never had been changed, changed the oil and filter, the filter weighed about two pounds drained, flushed the coolant system, ran engine flush through it (before oil change) and followed the directions to the letter. Now with all plugs changed, it runs great! EXCEPT it still has no acceleration. It occasionally tries to shudder but if I idle it up it stops. What I did notice by chance was the transmission radiator was getting extremely hot with it in park and only idling. This tells me that the problem may be the transmission. I checked the fluid at heated temp, and it's passed the full mark by about an inch but it's as pink and clear as can be, like brand new oil. When I'm on the road and I floor it, I can get the rpms to 4k but it feels like I'm trying to tow a train behind me and it just won't go. I live in Denton, TX and around here you NEED take off power or else these idiots will ran into your *** when getting on the highway. So should I get the transmission checked out? Btw, it's 4wd, and 4h and 4l work like a charm. I was almost thinking the fuel pump wasn't working great because after I changed the fuel filter and turned the key forward to fill the fuel lines, the pump made an awful sound, kind of grindy. But it hasn't done it since the lines got filled with fuel. I've also changed the air filter and checked the pcv for cracks and 90% of all other vacuum lines. The second day I had it, yesterday, it ran like a brand new truck for five minutes till it got warm. I accidentally smoked the tires because I wasn't expecting it to take off the way it did, it was awesome. But now it's like I've got a Briggs and Stratton trying to push the truck. Sorry for such a long post, just trying to give as much info as I can think of. The check engine light was on, it threw codes 0344, 1000, 0022, 0012, 0340. But after I changed everything and reset it, the light hasn't come back on yet. I know those codes point to the crappy timing system, but if it were timing, wouldn't the idle be consistently bad instead of when everything heats up? Any help would be greatly appreciated. Thanks!

 

You may want to go to a muffler shop and get the cats and exhaust checked for restrictions and excessive backpressure.

What weight oil and brand of filter did you use?

I'd siphon some tranny fluid out so it's not above the full mark warmed up idling in Park.

 

Havoline 5w20
Bosch filter

 

Check the brakes and make sure they aren't sticking. You should be able to do this by putting your hand on the center of the wheels after driving it to verify they aren't overheating.

 

Will do. I'm going to disconnect the cat also to see if anything changes.

 

Unhooked the cat, ran better, but after about fifteen minutes it started feeling like I was towing something. I got to the house and checked the brakes, the rotors are searing hot, all four. I didn't use the brakes that much while driving. Are all four calipers bad or is it in the brake system? I can replace all four but it's a waste of money if it's the brake booster or something simple like bad fluid.
Oh. And the check engine light came back on.

 

It's throwing new codes, misfire on nearly all cylinders. Starting to think it's the timing system. Guess it's time to put it in the shop and have it looked at. Almost wondering if it's cheaper to drop a brand new engine in it.

 

"New" 5.4 3 valves are quite expensive. You can't buy new, just used and rebuilt - and a reman with installation is about 7 grand.

I'd get the brakes looked at by a pro first.

 

I don't think it's the brakes, when I start it and just let it idle and warm up, it starts running like crap after it's warmed up.

 

^^^

Higher priority - you can drive a truck that runs like crap but you can't drive it if the brakes are burning up.

 

With all 4 calipers sticking, I would at first suspect the master cylinder since it is common to all 4. Of course all 4 calipers could be sticking too. And it could be the flexible brake hoses collapsing on the inside instead of allowing the spring in the master cylinder to pull the caliper pistons back releasing pressure on the pads.

Brake rotors get hot from just normal use, but if you place you hand on the middle of the wheels, it shouldn't be all that hot. You should be able to keep your hand on the wheel. If the wheel is too hot to keep your hand on it, then the brakes on that wheel is sticking.