Ford F150 - Loss of power 2000 5.4L

AJW · Posted: Thu Jul 03, 2008 10:32 pm Post subject: Loss of power 2000 5.4L

Hello All,

I've got a 2000 5.4L 4x4 with 140,000 KM's that has recently developed a strange loss of power when the engine is hot, and ONLY when its completely warmed up. When its cold it drives and accelerates normally (even better now that the new plugs are in).

Upon acceleration it seems the more gas I give it, the less it accelerates until I hit about 2500 RPM or more and then it acts more normal. Its almost like the engine is choking or something, but does not sound like it. No weird engine noises at all, and I usually pay pretty close attention because any little weird noise drives me crazy.

That being said, I've checked the air filter (K&N) which is totally clean and not overly oiled, I've cleaned the MAF. I've replaced the fuel filter which was a tad bit plugged. I've replaced all the spark plugs which were still the factory ones I believe. I've checked for vacuum leaks and everything seems fine there as well as the PCV valves (which I don't think would cause this anyways). I've also run injector cleaner about 3 tanks of gas ago. The transmission fluid level is fine and I'm kinda scratching my head here...

Two things have coincided with the development of the problem.

One, its gotten pretty hot here and it seems that as soon as it got hot, this problem started and its been hot ever since so I can't test it in colder weather. By hot I mean over 30 degrees celsius (I'm from Canada) so that'd be about 90 farenheidt (but really the truck shouldn't act like this in that kind of weather). The truck acts like this regardless of whether the air conditioning is on or not.

And two, I fueled up where I normally do and have never had an issue with getting bad fuel from the gas station. But it is possible that I got a bad batch or the sludge sitting in the bottom of the tank.

The engine runs as smooth as ever and doesn't have any hiccups at all. No jerking or anything like that which would indicate a possible misfire. The tone of the engine doesn't sound any different, it just lacks power until the RPM's get up a bit.

Do you think its as simple as bad fuel or any other things I could check? Possibly a plugged catalytic converter?

screwon23s · Posted: Fri Jul 04, 2008 12:13 am Post subject:

well, that sounds like a problem that i once had. i dont know if your enegine is the same as mine but in mine every cylinder has a coil and a couple of the coils went bad. once i put the new coils in it worked perfectly.

nickl911 · Posted: Thu Nov 13, 2008 2:24 pm Post subject: 97 expedition 5.4

i have the same prob i changed 8 coils and cats and all 02 sensors air and fule filter and no codes but it feels like im towing a train i cant get the tires to break free in the dirt but over 2500 to 3000 rpm it hauls just getting it there is the prob

headers high flow cats exhaust

metblu1 · Posted: Thu Nov 13, 2008 5:04 pm Post subject:

sounds like as soon as you cracked the throttle you get to much fuel untill the engine is sucking in enough air to mix with the fuel. make sure the fuel pressure regulator is not losing vacuum off idle. a quick drop when you first come off idle and then with steady throttle you stablize. vacuum can ok? Maf could be clean but still bad. And also the barometer that measures altitude for proper fuel mixture could be usually part of the maf or map sensor. mine was bad in my cougar, 4.6 was reading i was at 10,000 ft elevation wow was my junk off... hope i helped ay .

surfsean24 · Posted: Fri Nov 14, 2008 6:06 am Post subject:

Check the coils and your plug wires. I had the same problem which turned out to be the plug wire being fouled up in the boot. It would runn fine when cold and stumble on light acceleration, but if I floored it and the tranny dropped a gear it would be fine. If you don't have an error code yet, you should be getting one soon for a cyl misfire. If you get a code, find out what cyl it is, swap the coils, and clear the code. If the code comes back for the same cyl, the coil is fine. To get a code to kick, I wouldn't rev the engine up. I would keep it at an RPM where the engine stumbled. If you can get a code it will make your diagnosis easier.

stimy2001 · Posted: Fri Nov 14, 2008 6:14 am Post subject:

I had the same problem and turned out to be a weak fuel pump. When the pump would get warm it would start failing. If I stooped and fueled up the problem would go away until the pump warmed back up. The cold gas cooled the pump down and caused it to work better. You might want to try this it will not work on a full tank but 1/2 or below it always worked. Drove me crazy until I thought about what was going on. You also might want to check the fuel pressure when it acts up.