Hey guys, last weekend I changed my oil and replaced by spark plugs with autolites as my engine was running a little rough. Everything was fine and dandy and today I noticed again the truck was running a tad rough. Nothing too crazy but I decided to take a look under the hood while the engine was running.

Incidentally I put a hand on the number 3 spark plug wire and felt a knock through it. Grabbing onto the boot I could also feel a knock. I made sure the plug was in securely which it was. Unhooking the fuel injector made a change in the rpm's but the knock was still there.

I was wondering what you guys think might be the problem? I was thinking either bad lifter or bad rocker? My distributor is old I believe, I'm the second owner and the previous didn't take too great of care, could that be the issue? I thought not as if the plug were not firing there would be no change in RPM when unplugging the injector. I had champions in there previously and when I took them out there didn't appear to be any damage to the plugs, but I wasn't specifically looking for it either.

Anything you guys can add to a differential diagnosis and how to rule things out is much appreciated! Forgive my ignorance if I am thinking of the problem entirely wrong and let me know if I can clear anything up. Thanks!

 

Did you try feeling another plug, to see if it felt the same? How hard of a thump was it?

 

Thanks for the quick reply. I felt cylinders 1, 5, and 2 and none of them had the same thump. It didn't feel that forceful like maybe someone tapping the other end with a mallet.