my truck is bogging down in all gears(manual), it only bogs down when i try to put it under heavy acceleration. ive replaced the plugs, wires, cap,rotor,and fuel filter...still no improvement.what could this be? injectors? coil?sensor? i just need some answers as to what it may be and how i can fix it. im not to good with mechanics so please bear with me.
I recently replaced the coil on my 140000.00 mi 93 4.9. It would fall flat on its face (so bad you could not hear it running) when I would put it to the floor, any gear any speed or just sitting idling. If I held it long enough it would stall. If I got out of it in enough time it would run almost normal ( slight roughness). I could not find the source, switched tanks, replaced the fuel filter, popped the cap/rotor/wires and pulled the plugs and cleaned everything... no change. Just so happened that as I passed by the engine bay while it was running in the garage I heard it "snap" a few times than I knew it was spark leaking out. I could never "see" the spark but could hear it. Decided it must be the back side of the coil. Removed the coil and the plastic protector was bulged out from rust. $18.00 at Murry's and it runs like a brand new truck with 140000.00 miles on it.
BTW I never got a check engine light and I never bothered to pull the codes. The day I bought the reader was the day I heard the "snap".
Code readers are handy, but all they do is tell you what circuit needs attention. You still need to trouble shoot the circuit to find the actual problem. You can test the sensors with a meter if you find the proper readings for them. I bought an AutoXray, monitor, freeze frame, the whole works, about 4 years ago for $400 so it's not a $29 cheapo and I keep it updated. Still the most use I get out of it is turning off the check engine light for people. The analyzers mechanics use cost in the thousands to be capable of telling you exactly what part to replace and they're still not always right.
I also think it sounds like a bad fuel pump. When mine went, it would fall on its face when I floored it. Other symptoms were a hard shudder when starting. Usually it would not fire the first time I cranked it. I put in a Napa replacement pump for about $140, and haven't had a problem since.
assuming that the ignition, cats, etc and everything else are ok...a known remedy solver for part throttle/hesitation/bog is to install a restrictor plate reducing the holes to 3/8" inbetween the EGR & manifold.
On a 94, you can pull your computer codes with 5 minutes and a paper clip, and it'll blink out "morse code" with the check engine light (or you can use a continuity tester/multimeter and count beeps/needle sweeps). Check the following links:
Then look them up on the same sites, either 2 digit or 3 digit codes. It's daunting at first, but after one or two tries, it's boring simple. It'll give you a GREAT head-start on what to look at, and all you have to do is steal a paperclip from work.
Bogging under load will be either EGR (too much), like folks have said before, or a lean condition, probably caused by a bad O2 sensor (or a bad EGR, if it's not allowing any exhaust at all).
My 88 had both problems, got great MPG and had no power. It threw one code for "rich all the time" and another for "EGR valve not moving". "Rich all the time" caused it to run the engine lean, and the EGR valve really wasn't moving, so it was getting even more oxygen than normal under cruise because it wasn't being displaced by exhaust. Ford changed the EGR control system frequently, but on my 88, the vacuum solenoids were impossible to find.