I give up. My 99 4.6L pings unless I run premium. I have a K&N filter, so I thought it may have fouled the MAF sensor. I've cleaned the sensor with no improvement. At 66k miles I've been led to believe that it's not the plugs but I'm considering replacing anyway.

 

I am in the same situation. My 97 pings a whole bunch upon accelerating, I cleaned the maf and it helped for a day or so and now it does the same thing. I am going to change the plugs soon and see if that helps any. Dosent matter what gas I run in it either.

 

I have had this forever with my '97 150, and can only get it to happen on demand when hauling my horse trailer. My parents had it in their bronco and the dealership could never get it fixed. I had new spark plugs done 10 months ago. I took it in today to get something flushed, don't remember what, but I hope this gets better because at the end of the month I will have to haul from Dallas to Houston, and don't want to be along side of I-45 with no engine.

I have only ever used 87 grade fuel and am about to turn 130,000 miles.

What is the MAF?

 

It's the maximum air flow sensor, and is mounted between your air filter and intake. The K&N filters have a light oil coating which can foul the sensor. It's relatively easy to clean but you have to be careful.
I found a posting 10-12 months ago on this site where someone had posted pictures and instructions on how to clean. I don't have it anymore but it should be easy to find.

 

I got the same thing(pinging that is) if I use anything less than 93 octane. With 93 it goes away. Ive seen a simliar post on here a while back about this issue. Do a search for pinging or detonation, im sure you will find it