I have a 1997 Ford F150 XLT 4x4 4.6L V8. I used to put regular unleaded in the truck and it had a sound like the one you hear when you are shaking a spray paint can. This happened when I accelerated to above 50-60 MPH. My mechanic friend who also drives a F150 told me to put premium gas in it to smooth that out. Guess what, that worked perfectly. In older F150's with older engines, regular unleaded gums up the system. Since I have been putting premium gas in the truck it drives without that clacking sound in the engine. Now of course there may be something more going on in the engine which I freely admit but if you think putting premium gas has no effect, you would be wrong.

I also today(May 3, 2019) put mid grade 89 Octane in my truck and so far it also is driving without that clacking issue.

 

Maybe you've got carbon buildup causing pinging, and the higher-octane fuel is masking the problem?

 

I would agree. I learned this from a YouTube Mechanic named Scotty Kilmer. If I clean out the carbon deposits then regular unleaded would be fine.

 

Dump a bottle of Redline SI-1 in the tank, fill it with regular gas and drive it, then use top tier gas, like Chevron, Shell, etc and you should be good to go. Techron works well also to clean out carbon and injector mung. No need to run premium. Regane also works. whatever cleaner you use make sure it has PEA in it and it will clean the system and remove combustion chamber build up.

Another thing that helps on these trucks is installing an oil catch can in the PCV line going into the throttle body. the vapors (water and oil) from the PCV system will condense in the can and stop it from coating the inside of the intake and going into the combustion chambers. I only have to empty my can when I change the oil.

 

Would using the Redline SI-1 or Regane safely remove the "Clacking" sound when I use regular unleaded gas? I am concerned those additives may make things worse and require major engine work. Its my primary vehicle so it has to run. My goal is to remove the "Clacking" sound both at acceleration and first start idling, be able to use Regular unleaded gas and clean out the carbon deposits. Thus the truck's engine runs smoothly. It only has 174K miles on it for a 1997.

 

A "clacking" sound that comes during acceleration and goes away with higher octane is probably engine knock (also called pinging). It causes a lot of damage in the cylinders. Don't drive like that! Cleaning out the carbon deposits with additives like were mentioned above might solve the problem. Or you can use higher octane gas. Otherwise check the forum for '97 - '03 F-150s where people have specific knowledge of your engine hang out.

For older F-150s with older engines regular unleaded does not typically gum up anything. In our case (not so much for your newer '97) usually retarding the timing is the fix for engine knock.

And as several people have already said, on the '96 and older engines there will be little, if any, gain from using high octane, and possibly even slight losses. It should only be used as a Band-Aid to address knock (and cleaning carbon deposits or retarding timing would be a better fix then.

 

Zombie150,
The PCV line Oil Catch Can, I've never heard of such an apparatus. If you don't mind, please provide a part number and picture of it installed, this has peaked my interest. Thank you