Ok some background on the truck.... It's an old state truck apparently they were having the same problem. It has new cap, rotor, plugs, and fuel pressure regulator. When I initially started driving the problem seemed to change when you switched tanks. After testing the fuel pressure the rear tanks fuel pressure was low and didn't change when you disconnected the regulator. I corrected that by replacing the rear fuel tank pump. Fuel and flow are correct now. I've run both tanks dry and refilled with 89 octane and the fuel looked clear without any seperation after a day. I also ran the self test on the computer which gave me the TCS error code which has since been cleared. Currently it's not showing any codes. The distrubutor advances as it should during the test. I've been leaning toward the spark-knock sensor. Since there's always spark knock before the problem happens. I would think it would trip a code though.
Under acceleration would the computer advance the distributor until it detected the knock and then back off or is it a set amount?
It seems to be worse or sooner when it's warmed up. So my second thought is that this is one of those vehicles that has two tempature sending units one for the gauge and one for the ECM. Would keeping it in a cold loop cause this? Although I haven't been able to locate a second sending unit and the book doesn't mention one.
I really appreciate the help with this guys, this thing baffles the hell out of me everytime I drive it.
McGyver
P.S. When I went to the Ford dealer to buy the friction modifier I told them which one I had and they had to get a different bottle then the one they normally sold. I told it them it was for a E4OD in a 93 F150. It was in a white bottle where the other one was in a yellow. Any thoughts on this?