Fouls out plugs but does not use oil - 1991 Ford F150

Are the plugs wet yes/no? If so what is it antifreeze or water also knowing what kind of car it is will help a lot because of the design but if it's antifreeze and a 4.6 engine the thermostat/crossover gasket is leaking and antifreeze is running down the heads and into the spark plugs chambers on either engine bank this is provided that you are using antifreeze in your radiator if it's water same thing if your using it to cool the motor but if not and water is present the inner fender splash guards are missing and big puddles of water when hit will splash the water inwards towards the engine and will run into the cylinders also high pressure car wash will do it look at your coil on plug boots if no moisture is there they could be soft or cracked and the positive coil firing voltage is jumping to ground and is not firing the plug/s involved and they should be blackened with soot smell the plugs and feel the metal casings if slippery there's antifreeze if just wet water none of the conditions described are present change the mass air flow sensor and I almost forgot to tell you to bend the spark plug boots back and forth if the are bad they will break and also roll them in your fingers looking for brittleness and cracks also you may have a bad batch of gasoline in your tank check all above first and open the throttle body plate with your fingers if it's very black inside a good cleaning with Berrymans fuel injection cleaner and a change to higher octane brand name gas will correct this and I'm not there so if your using delta,valero,usa liberty or any other garbage fuel this is a indication of why your having the problem there's no detergents in those fuels and they are made from the crud at the bottom after the name brands have been refined and the higher the octane rating the more stable the fuel burns but the junk fuels burn very quickly and varnish build up is eminent in the cylinders your injectors and your throttle body the junk fuels make it build up at least 3 times faster than higher quality fuels and there's no detergent helping to keep things clean so if you think that saving 10 cents a gallon is worth the cost of replacing injectors or other components plus labor maybe $600-$800 think again and if a tow is involved well I guess you've hit the jack pot oh boy 3am on the side of the road good luck a taxi mechanic here in nyc 50+ years of repairs and motors with 450,000 and still running is where this came from and next time give your specifics on the vehicle my genies on vacation and the crystal balls still on loan from new years in Times Square but I tried my best good luck stephen