Help please, I have a 1989 F150 with 4.9L and 4 speed overdrive manual transmission. It has 152k on it. It misses randomly. Most noticeable in 1st & 2nd gear but sometimes in OD as well. I have changed fuel filter and then distributor cap & rotor. Each time it runs smoother, but still misses randomly. Can't really narrow it down to a specific set of circumstances as to when it misses. Is there a system that controls spark advance that I should be trouble shooting? Thanks for any help offered.

 

When was the last time you changed the spark plugs and wires?

 

That is next on the list. Also saw a comment that sometimes plugs work themselves loose. I will do plugs & wires this week. Thanks for the tip.