i looked on a couple of plug sites and supposedly lead fouling, which i don't have because of no lead in modern gas, will cause rough idling or hard miss only at higher rpm's. the color of plugs is consistant with lead fouling but not the symptoms. mine has a rough idle and a bad miss at idle and through the whole rpm range. doesn't make any sense. is it possible that the new cats could somehow have lead in them? or maybe antiseize got in the cylinders? i'm just grasping at straws here because i don't know what else to test.

 

also island time, you could check autolite, ngk, or accel web sites. i found these out from googling yellow plugs. they had very informative pictures, descriptions, and causes similar to what krooser sent. very informative but unfortunately, what i found didn't help my case.

 

From VDL Fuel Systems

Additives in the fuel – sometimes when you change fuel brands you will see a change in the look of the insulator. Usually it is a color change indicating a different dye or additive used in the fuel. It may have a yellow color tint or it may have a crystallized appearance. The yellow color typically is a sour crude having a high sulphur content, (western crude oil is a sour crude having a high sulphur content), or it can be from a high amount of lead additive. As for the crystallized appearance some tracks add a small percentage of alcohol to their fuel to absorb the water/condensation that gathers in their large, very seldom full, storage tanks. This alcohol with it’s water can give the insulator a crystallized appearance.

From automotive basics for the at home grease monkey

A red, brown, yellow, or white coating that forms on the spark plug insulator is a by-product of combustion, resulting from additives in fuel and oils. Usually, scavenger deposits, as they are called, have no ill effect and are quite normal. Sometimes, however, they can cause misfiring at high engine speeds under heavy loads. If the insulator is not too heavily coated, the plug can be cleaned, gapped, and put back in. Occasionally, even after cleaning, an invisible path for an electrical short circuit remains and a plug still misfires. Then you must replace the plug. (Under some operating conditions, scavenger deposits melt and form a shiny yellow glaze over the insulator. When hot, that glaze is a good conductor of electricity; the spark follows the deposits instead of jumping the gap, and the plug misfires. You can prevent the formation of such glazed deposits by avoiding sudden loads such as wide- open-throttle acceleration after a long period of slow-sized driving or idling. Once formed, the glaze is almost impossible to remove, and the plugs must be replaced.)

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That's all I can find. I'd start narrowing down possibilities starting with the cats since that's the last thing you did to the truck before this happened.

Try running it with a fresh set of plugs and no cats to see what happens.

 

thanks a lot dixie460. i'll definitely try that. I also got to talking to a couple o master tech's and one thing I learned is that if the temperature of the cylinders get too hot, the deposits left behind from the combustion process can burn onto the plugs causing the glazed yellowish appearance and rough running. 2 things I was told is that the egr valve can get weak. if that happens, the exhaust pressure can cause it to open when it is not supposed to and increase the cylinder temperatures. also, if there is trash in the injectors, the injectors will cause fuel to dump and pool on the piston heads causing kind of a minor explosion inside the cylinders instead of the injectors misting the fuel in and getting a controlled burn. that could possibly cause the temps to increase also. the egr valve I can remove and check. can't check the injector possibility until me and a friend build a device to pulse the injectors in a solution bath to clean them. when he gets the specs on building that, I will post them. I'm not a paying subscriber, so I don't know if I can do attachments or not. if not, send link to your email and I will send it to you so you can post it if you wish.

 

Dixie460. you rock. I took your advice about running without the cats. instead of dropping the cats, I removed the o2 sensor. truck ran ten times better than it has run in a long time. now I just have to figure out if the cats is the problem or the o2 sensor itself. thanks a lot man. I owe you a steak dinner.

 

Awesome, glad to hear it and you're welcome!

I can't seem to find it but there was a thread on here showing how to rebuild your fuel injectors, if you decide you need to do that. Pretty much all you do is replace the inlet screens, pintle caps, and o-rings. Oh and let them soak in B12 Chemtool overnight before reassembly. Maybe someone else has the link or can find it.

 

Here is the link to the injector rebuild thread, I used the parts and instructions from it, super easy to do.

https://www.ford-trucks.com/forums/1...d-install.html

 

found out something. if replacing catalytic converters on a 302 (not sure about other motors), replace muffler(s) as well. i was talking to a guy and he said that sometimes when the cats start to deterioate internally, the catalyst (honeycomb) can start breaking apart. when this happens, the trash from inside the cats will get into the muffler causing the baffles to get blocked up therefore causing exhaust to back up into the motor. this will dramatically increase the temperatures inside the cylinders causing the trash left over from the combustion process to burn onto the plugs. this will cause that yellow glazed build up on the insulator and electrodes which will cause a major misfire resulting in lost gas mileage, performance, and you beating your brains in for almost a year trying to figure it out. i went to drop exhaust at cats to test this theory and notice my tailpipe about to fall out of muffler. i took the system out from the cat back, installed a muffler and a turn down pipe and now the truck runs better than when i bought it. it even pulls hills in fourth gear, increases speed going up hill, and i now have to stay out of the throttle. this has been 9 months worth of headaches, but i finally got it. so, if anybody reads this and is replacing catalytic converters because they went out, do yourself a favor and replace the muffler as well. believe me, you wont regret it later. thank you so much to every one who posted trying to help me out with this and i hope i can return the favor one day.

 

Good info, if I ever come across yellow plugs in an engine that runs like crap, I'll have to (attempt to) remember your experience with clogged exhaust. Thank you for coming back and closing out the thread with what you found and did to fix the problem!

 

Thanks for sharing that with us. I'm gonna put that in my files. Glad you got it all straightened out and your truck is doing good.