my 87 F-150 has recently started acting up by "missing" while its driving as if the engine stops for only a fraction of a second. it causes the cab to shake and the RPM's to bounce around. this issue started by it only happening maybe once a month but recently as the weather got cold it happens every time I drive it and it happens constantly. (see video)
I've recently replaced my whole distributor with a new ignition module and the majority of the fuel system for a separate issue i was having a few weeks ago. but the issue i was having ended up being my distributor drive gear broke loose. the truck drove fine for about a month then this started. I've read the codes from the trucks computer and i got
-33 (EGR valve fault)
-25 (knock not sensed during dynamic response test) ill add more about this later
-44 (thermactor air system fault)
i unplugged my knock sensor as i read if its faulty it could be telling my ignition to retard timing momentarily. this did not fix the issue.

maybe im getting a bad ground somewhere?
maybe a vacuum leak?
ive also tried cleaning the MAP and replacing all plug wires, cap, rotor ext. that as well didn't solve the issue.
i read somewhere that someone found corrosion in some connection for there coils. so i cleaned about every electrical plug i could which also didnt help.
does anyone know what might be causing this???
i dont know if its important but it seemed as if it does it more often when its cold... i also haven't seen any evidence of it happening at idle just while under load (accelerating and in cruise)

 

I would pull the EGR and make a blank off plate for it so you can rule that out.

I dont like the way the speedo also jumps the same time the tach jumps and to me that tells me it is electrical in my book.
I think there is a ground for the computer over by the battery and because it is by the battery it can fail so I would look at that as it is easy.

The second place to look at is the computer. Pop the top and look at the capacitors. They have been known to go bad, leak, turn brown.
If they have leaked / turned brown the computer is bad and needs to either be replaced or the cap replaced.
Bad caps have been known cause all types of problems.
I got nothing else at this time.
Dave ----

 

A friend of mine had a very similar problem and after he did a lot of parts swapping it turned out to be the fuel injector.