What could it mean when an engine accelerates strong at heavy throttle, then become unresponsive up to wide open throttle?

I ask because both my Prelude and my Ram suffer from a similar problem. If I hit the gas up to 3/4 maximum, my Prelude accelerates strongly then becomes flat with no change to power if I go WOT. My Ram accelerates strong up to only 1/2 throttle, then totally flattens out.

Prelude has K&N intake, 4-2-1 aftermarket exhaust and newish NGK plugs and wires (haven't yet replaced the distributor cap and rotor). 266,000 miles.

Ram has a round open-element style intake and brand new exhaust work including a high-flow catalytic converter and Turbo Thrush muffler. (170,000 miles).

Both vehicles run premium BP gasoline.

Running old engines, I suspect the answer to my problems is simply old age/wear and tear, but I'm just curious as to what could cause a fuel-injected engine with no CEL to run flat at WOT but strong prior to that. In comparison, my Dad has a 2004 Ford Expedition with a Triton 5.4 V8 and 170,000 miles that runs strong as hell even at WOT...

 

I was going to say clogged cats but I see youve covered that. slipping clutches?

 

adjust your throttle cable at the throttle body to make sure the throttle plate is opening up all the way when you go WOT. the cables like to stretch over time. also get a hold of a timing light and check your ignition timing. if the light seems choppy when you use it, i'd spring for a new cap and rotor if you've already done the plugs and wires.

prelude sounds like an timing issue to me though. how does it idle?

 

VeeSykkz: My Prelude's clutch is a bit soft, but I don't think it's soft enough yet to start slipping. The Ram is an automatic.

full Circling: I can't honestly say I've ever thought of the throttle cables. I'll check them out later today. The Prelude idles fine though it'll sometimes high idle (1,100-1,200 RPMs) in neutral after driving.

 

Check tips

 

high idle is prob from a big plastic screw that backed out inside of your fitv on the intake manifold. take it off and tighten it back up. make sure to seal it back up when you put it back on w/ some permatex ultra grey, or get new OEM gaskets if you do. fixing the high idle prob wont fix the power problem entirely, but it will def help.