Mr. FordFxr; I am the guy from last night with the 1986 f-150 4.9L 6 cyl, with the "Miss"-
Here is what I learned in school today; First, I took out the plug in cylinder #1, and hand-cranked to engine to find TDC, after playing with it a while, I got to what I thought was TDC (turned out later to find it was about 2 degrees off). I then carefully inspected the Damper and pulley for timing marks, and were NONE, other than the large notch (which when at TDC on #1, was located directly down at the bottom of the engine; near oil pan). I then took out a hack saw blade, and made my own small mark at 0 deg. TDC, and marked it with paint. After replacing the plug, I disconnected the spout, and started the engine. With the timing light on #1; my mark was seen at about 2 deg BTDC (2 degrees off). When I moved the light to cylinder #2; The "red" wide notch was exactly at 0 deg TDC. When I reconnected the spout connector, the tim.ing shifted to 12 BTDC on cylinder #1, then when I checked #2 (with "red" wide notch on damper) it was exactly at 10 deg BTDC. So, with it all, it looks like the timing is good (although I still do not understand why the factory timing mark is that far off, with no secondary markings aligning with either the passenger or driver side timing guages??).
However, the truck was still periodically "missing".
Next, I took some carburetor cleaner and went over intake manifold (at the head), and noted no difference in the engine idle. I did the same across the base of the carb. and TPS assembly, and had a very slight increase in idle. So, I tightened the carb a little bit (but not much, in as it was really not loose), and repeated again, with no change in idle speed. Also sprayed all of vacuum lines, and they seemed O.K.
Next, I took you suggestion from last night and removed the EGR valve. Upon inspection; this was the "nastiest thing" that I have seen in quit a while. It was horribly carbonized, and crusted up all over (on the rear diaphragm section). I cleaned it up and put the cardboard gasket in (Using a little RTV on either side of the cardboard), reinstalled it, and then started the engine, and it did in fact make a difference, but did not take care of the entire "miss", but it did help. Found out from Ford that this part is obsolete, but was able to have Ford locate one, which will be here Wdnesday (showed the parts guy at Ford, and he indicated "it was definitely shot!'). Now, I continued to investigate (with EGR Blocked off), going back to the electrical system; and noticed that when I pull the plug wires on #3 or #4 cylinders, it had NO affect on the idle. So I changed those two plugs, with the same results. Next, changed in a new set of plug wires (just in case), and again no better (in fact, I went back to the old wires). Now the truck is running "crappier" than it was originally. So now I am back to the original plugs and wires, and it is still running "nasty". The miss is now persistent, and not occasional as it was before. Could blocking off the EGR have something to do with this? I remain confused with what I am seeing.