I have a 1986 f150 with a 351HO engine. What brand spark plugs were originally used in 86?. I want to change plugs and need some recomendations. Reason for changing plugs to get little better perfomance and gas mileage. The truck only has about 3000 miles on a rebuilt motor.

 

Motorcraft, of course. Read the VECI label, usually on the core support near the hood latch, but sometimes on the air filter cover. It specifies the plugs & other info. You should put ALL the truck's details & history (as much as you know) into your signature so it shows with each post, as this page explains:

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Phone apps don't always show signatures, so you may need to switch to a real browser in desktop mode on your phone, or just use a desktop/laptop computer. Put your location in your profile & upload an avatar of the truck. The more pics you post of the truck, engine, wiring, labels, & undercarriage, the more likely we can help you. Not all its details are relevant to these issues, but you don't necessarily know which ones are relevant, so just put everything in now.

 

I never noticed any issues with various sparkplugs in my 1993. I don't know if the older trucks were less finicky than they are today.

I've used many brands through the 200,000 mile life that truck had.
For the cost of Motorcraft at autozone, you probably aren't going to over-spend when considering an Autolite option.

 

I believe Motorcraft plugs are made by Autolite anyway.
the Newer F150 come with NGK plugs made in Japan.

 

...and Ford electric fuel pumps for these trucks were made by Bosch; but Bosch-branded fuel pumps are NOT built the same way as Ford/MC-branded pumps. Just like Jaguar S-types came off the same assembly line at the same time as Lincoln LSs, but they're NOT built the same. If you want a Ford/MC spark plug, buy a Ford/MC spark plug. And buy the one Ford recommends for your specific application.