I'm posting this message in both the Engine and exhaust categories cause i dont know what is givin' me the problem!

I have a 97 F150 4x4 Ext. Cab (w/ 55,000 miles)...i have a question i can't figure out...

The exhaust or engine is making quite a bit of noise. The sound is very hollow sounding and much louder than the flows usually let out. This sound occurs at around 3,000 RPMs but only after sitting for about 9+ hrs. After a few high revs the noise will disapper. Along with the noise is a problem i am more concerned with...when the truck hits 3000 RPMs and the noise occurs there is a considerable drop in acceleration...even when floored the RPMs almost refuse to keep going up...my first thought that could relate these 2 problems together is the EFI...if it is clogged then the fuel wouldnt be getting to the engine (accounting for the loss in revs) and therefore the exhaust would make wierd noises...after the high revs however the truck runs as new (almost as if the blockage has been cleared)...another curious thing about it- is that the engine will not make this sound or have any trouble while in Park, only while in Drive (which makes me wonder if it really is the EFI)...i've taken the truck to 3 shops and no ones been able to fix the problem...please, someone out there has to have an idea whats goin on! Thanks in advance...


------------------
Brandon Warford
97 Red F150 4x4 Sport
big mudders, 3" lift and lots-o-goodies

 

Sounds like fuel-starvation to me.

------------------
Y2K™

XLT SC SB 5.4L 3.73LS

 

I had something similar that made me take it into the dealership to be checked out. Problem would occur when temperatures were hot outside and WOT from a slow roll. Tremendous noise forward of the cab would occur. Power would fade in and out but would eventually pick up speed and the noise would go away. The dealership checked for codes and there were none, but they also reset my ECM. To this date no more trouble. Knock-on-Wood. Comment was made in an earlier thread that possibly the torque converter is not locking up like it is supposed to do. The computer kind of looses its mind when the tempratures get warm not knowing what to do in order to prevent excessive emissions. When the temperatures get warmer the emission components begin to take over. I know my electronic trainy is effected, becuase performance begins to suck when the air is hot and humid. Just my .02$

------------------
99 4X4 XLT S/C with ORP
5.4L 3.73LS
Flow Master Dual Exhaust
K&N Filter w/ Intake Mod
Flex-a-Lite Black Magic 150 Electric Cooling Fan

 

Could it be that you have a plugged up exhaust? You stated that it makes a "weird" sound. This could be caused by a bad cat. converter or converter core parts going downstream and plugging up the muffler.
Had it happen on a Honda I owned, but it was high mileage when it happened.