I have a 1992 F-150 300 6cyl 5speed. And it has a miss or stumble at cruising speeds 35 to highway speed. (shakes like fuel shortage) Clears out on acceleration and is barely noticed at idle. This is a second owner truck with 284000 miles on it and everything I have changed was OEM parts. I changed the fuel filter (OEM) and when I drained it. Fuel was black coming out. I have changed the Cap rotor wires and plugs. Firing order is correct. Problem seemed better after fuel filter but has since returned. I am totally stumped now. Codes show nothing. And am to the point of changing PCM or fuel filter again. I have not ran fuel pressure or compression test yet. Any Ideas? Thanks for any help.

 

Well to answer my own question and to help anyone in the future. Turned out that spark plugs today are not built to very high quality specs. The brand new plugs (Motorcraft) that I had installed were the issue. The #3 cylinder had such a high resistance that it was not firing. After the parts house and I armed with a ohm meter found this we also discovered that the plug with the least resistance was made by Champion. This was out of mfg's that they had in stock. So when buying spark plugs take your ohm meter with you it could save you time and frustration. Now my 300 F-150 runs like a champ.