At idle you should see 38 to 42 pound of fuel pressure if you remove the vacume line from the fuel pressure regulator it should jump 46 to 50 pound these are the same pressure you should see while driving. On a hard pull when manifold vacume drops this will raise the fuel presure slightly the fuel pressure should never be below 36 pound.

 

Mike7333,

I have 157k on the engine. It's seen mostly highway duty though, so it's not in too bad of shape. I changed the plugs/wires/coils last year, 30-40k miles ago. I did have one problem where a coolant hose was leaking above cylinder #4 (rear passenger side). There was some coolant leaking on top of the engine and might have seeped into the spark plug. I don't want to check it because it's a pain to get out. Sounds like I might have to...