Couldnt find my original post on this, so heres a new one.
94 4.9 5spd 2wd
Truck sits a lot because I drive OTR and am not home very often. Few months ago she developed a miss. Engine rattles/vibrates during acceleration but hardly at all cruising. Tried injector cleaner, thinking fuel was bad. No change. Put new plugs in, #2 plug was broken when I pulled it out, and a couple were caked in sludge looking crud, but none were fouled, all looked to be burning good. No change. Was going to do new wires/cap/rotor, but the wires wouldnt snap down onto the cap, and I ran out of time and energy before I could replace them.
I noticed that one of the tabs that hold the pcv line in the valve cover was broken off, leading me to think its stuck in the valvetrain causing the issue, but I cant remember if I had noticed that long before this issue happened or not.
I also remember an issue similar to this I had on a 91 4.9 that turned out to be a broken starter (after I had given the truck away, of course), and this truck has had an issue of taking its sweet precious time starting for a long time, so there's another possibility.

I've done a couple 700 mile round trips across Texas since the issue started. Fuel mileage has remained consistent (which has always been kinda low thanks to the 4.30-4.56 gears the previous owner put in it for some retarded reason)(M5OD-R2+235/75r15+3000rpm@70mph=4.30-4.56 gr according to my calc's) but she does seem a tad under powered (obviously if its running on 5 cylinders). No leaks of any kind, exhaust smells normal, no white or blue smoke.

I have heard horror stories about the ethanol in the fuel eating at the rubber fuel lines and tiny chunks of rubber clogging injectors and regulators, so that's a possibility.
My biggest fear is that its a busted valve spring or rocker arm, which is a bit beyond my comfort zone mechanic-ing wise.

Just trying to make a mental list of all the things to check when I get back to the house. Any thoughts or ideas are always appreciated.

 

My experience is with older carbureted engines, but I wonder if you have checked for codes in the computer? It really can be your friend at times. Take the truck to any automotive parts store and ask them to scan the computer. Normally, there is no charge as they hope to sell you parts.

 

If it is skipping under load I'd look at the plug wires.

 

Check all your hoses for vacuum leaks

 

ugh...vacuum leaks....theres something Im not looking forward to searching for...lol

 

Do a search on Youtube for vacuum leak smoke test.
Using that is an easy way to find vacuum leaks.
Dave ----

 

https://www.bing.com/videos/search?q...69CE&FORM=VIRE

 

I had a 96 300 six that had a miss and I found the fuel injector for the dead cylinder wasnt working. It ended up being a bad connection somewhere in the harness. I just ran a extra wire from the computer harness to the injector. A cobble job but it worked. Dont know if thats what you have but its a shot.

 

I'm a carburetor guy, but start with the easy stuff before digging in and spending big money.
-Good grounds between battery engine and body
-Check all electrical connections, tight and clean
-inspect plug wires. If the don't look good change them. If cap and rotor are old or look bad change them.
-if you have a timing light check timing
-old gas? station sold you watered down gas?
-vacuum leaks
-fuel filter
-PCV valve
-compression test

A broken valve spring or rocker arm would probably cause some bad running, at idle and revved up. If its all stock I doubt you broke anything under the valve cover. Out of adjustment arms, if they are adjustable on the efi motors, maybe.