I have a 1993 F150, 5.0, E4OD. It has developed a sputtering sound which gets worse under a load. If the engine is idling or cruising (w/o a load) you cannot tell there is a problem unless your listening for it. This has been going on for over a year and it's driving me nuts.
I did a compression check thinking it was a valve or rings, it sounds alot like a bad cylinder. No real weird findings. I replaced the cap, rotor, wires and plugs - no change. I checked for sparkplug wire routing (crossfiring), good-to-go there also. Ran "high-dollar" injector cleaner through it - still no change. This past week I started pulling the engine apart really hoping to find a collapsed lifter - they all looked good to me. So while I had the whole top-end torn off I had a real lapse in judgement and put a new long-block in it thinking that I would just cover all the bases. Fired it up - problem is still there!:o Told wife - got a real nasty look and went back out to the garage.
Initially, when I first fired it up, the truck appeared to have been fixed. I believe now that that was nothing more than the computer running closed loop (hope I got that right) and running off of it's default until all the sensors started inputting info to the computer. As the engine started to idle down and warming up ( I was watching the engine oil pressure guage), the sputtering noise returned. I'm now thinking it has to be a sensor, a smog issue or even bad injectors. I'm at the point now that it may be going into the shop to get looked at by someone other than me (shade-tree).
When I pulled the upper manifold off it was full of crud. This led me to believe that there was a bad valve or rings. This crud was started from the back of the butterflies on the throttle body all the way to the intake ports on the heads. The valley was in great shape (a little brown) but that was it. A few of the piston skirts were scuffed also. Other than the large amount of black crud in the intake the engine looked good for 141,000 miles.
Anybody have any ideas?

 

have ya checked the exhaust...maybe cat starting to get clogged?

 

Thanks for the reply. I hadn't checked that. I'll have to give it look see. The thing about it is that after initial start up when the battery had been disconnected, the engine sounded "normal" again. It returned after it had warmed up.

 

My 302 in my '92 eventually let loose because I let it run too long like that. The first catalatic converter was plugged almost solid. I had reamed all of the guts out of the one I could get to.

I would suggest getting a new exhaust made at a shop, it will be cheaper than a new Ford factory Y pipe with cats, trust me I priced it all out.

Also would bee a good time to throw on a set of headers!!

 

Thanks FordMan,
I recently had to put the OEM manifolds back on. I found a crack in my JBA's (out of warranty now). I know what you mean about the performance difference.