ok, i got a weird problem here, but i think i got it figured out, but I'm curious what you guys think about the problem and my hypothesis.

the truck: 1995 F-150, 5.8 L, Vortech supercharger, E4OD, short tube headers, variable spark advance dial in-cab.

the problem: After the truck warms up, there is sometimes a misfire when the truck is idling at a stoplight. There is no misfire above idle... yet. The misifre is from the #4 cylinder. I know this because I have been replacing spark plug wires for #4 a few times now. The last time I replaced (and these replacements are just me swapping old spark plug wires that were probably replaced prematurely a month or so ago) the plug was actuall loose and there was a small degree or the white powder corrosion on the tip of the plug, and inside the plug wire. Everytime I replace, the misfire goes away for a few days, and then comes back. Sometimes, before I go somewhere, I just push that spark plug wire on a little more firmly and it wont misfire all day. So my thinking... exhaust leak on the #4 cylinder, ruining my spark plug wires (one by one...).


BUT: I mentioned the truck had variable adjustable spark advance in cab, so.... I discovered that i get the best fuel mileage (significantly) when the spark is RETARDED to the max on the dial (about 5-10 degrees). So since, the spark is more retarded that usual, the exhaust temperature is higher than normal. i think the higher exhaust temperature is adding to the problem of spark plug wires getting too hot so close to the headers. But than why wouldn't all my spark plug wires be causing misfires?


to recap: the exhasut temps are hotter than normal due to spark retard. A nagging exhasut leak is causing the #4 wire to give improper spark for idle speed.

Solution: replacement of exhasut headers with factory OEM exhasut manifolds, or better, higher quality shorty headers to handle the higher exhasut temperatures. Finally, getting a high quality set of splark plug wires with built in heat resistant coatings and such. Above all, I am interested in longevity of this truck.

How does this sound guys? Make sense, or am I way off? Sorry for the long story, and thank you for the help.

 

Sounds feasible to me. What you need to invest in if you dont already have one is an infared thermometer. That way you can check indivdual runner temps of the headers, maybe you have a partially stuck injector causing a lean cylinder, or a possible burnt valve or sticking valve.

 

i got a infared temp sensor, as well as a few thermocouples, so i may do a little down and dirty temp data for the headers. If I can significantly lower the header temperature, and potentially make the misfire dissapear by advancing the spark in cab, maybe I'll just do that. You can buy a lot of gas with the money saved in spark plug replacement and exhaust work...