1990 Ranger 2.9 with intermittent Misfire

[MrGoop]

I have a 2.9 that I can drive for about 20 miles at 55 mph and it will start to misfire on one cylinder ( well it feels like one cylinder to me ). If I drive it a little harder say 65 mph it will start missing sooner. I have changed the plugs ( twice ), plug wires and fuel filter.
Any Ideas???

 

[RyanL]

With the truck running, pull the vacuum line off of the fuel pressure regulator to see if a little fuel is leaking out. I ask because mine was leaking a little (along with a lot of other guys around here) and from what I have heard the fuel leaks straight down into cylinder 6 making that one cylinder burn real rich (possibly causing your misfire). It's just something that you could check out real quick before throwing parts at it. My main issue ended up being a flaky TFI (ignition module which mounts to the back of the distributor).

 

[jhammel85]

How about the cap and rotor? Did you do those?

 

[RustedRanger]

The FPR don't have to leak to be bad...mine didn't. It also worked fine when I got fed up and took it to a shop to have it diagnosed...until I drove home lol It was then I found out my cousin had a pressure tester the whole time.