Pinging at WOT?

You have too much total timing. The computer adds a set amount of timing so backing your initial timing solve the problem. DO NOT floor it until you can confirm the timing and adjust accordingly unless you like picking up engine parts off the floor. That loud embarrasing sound is two flame fronts fighting each other in teh combustion chamber (nasty stuff, the worst). So lay off and wait till u get it sorted out.

Find out where ur timign is. Ideally, set it at 10 and start adding 2 degrees at a time. So start at 10, take it for a test drive. No pinging then add 2 degrees. Keep going until you hear pinging then back it off 1 degree. TEst drive, then you should be good to go. Also, always use premium gas if ur gonna run advanced timing. If u wanna run cheap gas run 10 degrees of initial. If ur already at low timing (10 degrees) and still pinging try ur ACT sensor.

Pinging is caused by a number of things:
1.) Hot spots in the combustion chamber such as carbon deposits from high mileage or excessive oil consumption.
2.) Wrong heat range on the plugs.
3.) Too much initial spark advance.
4.) Lean fuel mixture.
Lean fuel mixture breaks out into several sub categories:
A. Vacuum leaks
B. Air entering the intake without passing through the MAF
C. Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D. Leaking exhaust gases from EGR valve at WOT.
E. Clogged fuel injectors.
F. Fuel injector wiring problems causing injector not to deliver rated flow.
5.) Computer problems: (computer problems are not common like sensor problems)
A. ROM has bad data in fuel or timing table. This should also set a code in the computer.
B. Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one.

Have you dumped out the codes?
Here's the link to dump the computer codes with only a jumper wire and the check engine light. I’ve used it for years, and it works great.
See http://www.batauto.com/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/article...c-iv_codes.html

Great info thanks!

A real common cause of "pinging" is the MAF sensor being dirty. It is especially comon with car that have a K&N air filter (an over-oiled filter can gunk up the MAF pretty good).

If you do an online search, you can probably find info on cleaning it. The process is a little more involved than I could briefly describe here.

It's pretty simple to do. All you need to do is get the right "security torx" bit, and some electrical contact cleaner. The sensor wires that you need to clean are very fragile, so you have to be real careful. You sould not touch them, just spray them with he contact cleaner. If any gunk needs to be brushed off them, I'd suggest just hitting them with the just the little bit of fuzz hanging off a cotton swab, and no the end of the swab itself. That's how fragile they are!

I don't believe that a gunked up MAF will throw any codes, but it is a cheap and easy fix to try first. It's worked well on a couple of my rides.