Expedition EB 2003 runs fine until after about 30min to an hour into operating temperature. Then it just seems to lose power. Feels like its being deprived of fuel. It's ******* with flat acceleration. Engine idle is fine, it does not feel like a hesitation it just does not have the power it does when cold. The vehicle has always been well maintained. This condition has been going on for about a year. About 6 months ago I had the dreaded manifold crack in the coolant passage. I replaced the whole manifold and while I was at it the spark plugs and coil packs. I changed the fuel filter as well. This didn't change the lack of power issue I am having. When the engine is cold its gets up and goes! but as the engine starts to get up to and into the operating temperature it seems I have to push further and further down on on the accelerator. The engine does not ping or knock but it feels like for some strange reason the computer is retarding the timing. I have run scans and it never has any error codes. I have cleaned the throttle body and MAP sensor with the proper cleaning sprays and still no luck. Any ideas?

 

The ECM could indeed be retarding the timing. It will detect spark knock long before you would ever hear it. At your next fill up try running 93 octane just to see if the engine power keeps up at the warmer temperatures. If it does spark knock is the likely issue.

 

That is a GREAT idea and something I'm going to try. THANKS!

 

Also dont overlook the IAC sensor. My wifes Excursion never threw a code and i never ran live data but I knew it was low on power but at only 107k when we bought it, I thought it was normal for the big X to be low on power thats when i remove the IAC and cleaned it, even thou it was clean it made a bit of a difference but not a whole lot, but thats when I decided to just buy a new Motorcraft just because at 154k and BAM!!! the thing felt like it picked up 35% of its power and with the swaped in 4.30 gears like thing whiplashes you on a acceleration. I have no clue how to test an IAC but worth to check it out.

 

Wouldn't there be a code if the knock sensor detected knocking?. On my other car the knock sensor(s) give a false signal and Code during inclement weather (maybe moisture).

 

No because that's what the knock sensor is supposed to detect. If you disconnect the wiring to the knock sensor you would get a code.

 

might also be worth testing your fuel pump pressure when it is up to "operating temp".