My 93 4.0 V6 explorer knocks horribly at about 25000rpm and up under throttle...especially if on a long grade. Higher octane fuel does help but does not eliminate the problem. I tried fuel system cleaner and it too helped but not cured. I recently put on an IFAB air intake and have a flowmaster cat back exhaust so I am wondering if the air fuel ratio is wrong? I was told the stock computer would be able to adjust accordingly to the new higher air flow but the knocks definetly got worse with the intake. Any suggestions? Anything I can program in (chip etc...) or might new plugs help? Thanks al lot for any advice...Take care...Matt

 

25,000 Rpm Ping is the least of your concerns. That engine should have blown up, if it could even overcome internal friction enough to spin that fast. I know, there's an extra zero there; just having a little fun with you.
Ping or spark knock is a fairly common problem to the early 4.0 OHV and is discussed quite frequently on these boards. The following treatments seem to cure ~90% of cases:
1) Decarbon the cylinders. Seafoam or equivalent seems to work well. Alternatively, get out on the highway and run the truck in 2nd gear so you can run the engine at 4000 RPM for a while to burn the carbon off. Ford has even recently issued a TSB that encourages drivers to regularly "get on the throttle" to get the engine RPM up and keep carbon from building up.
2) Clean the MAF filaments. Filaments get dirty -> computer "sees" less air entering the engine -> computer feeds less fuel into cylinders so it runs lean -> engine pings. Security torx bits can be found at most parts stores or tool outlets
3) Vacuum leak or intake leak downstream of the MAF. Engine runs lean and pings.
4) Loose lower intake manifold bolts. Allows a small vacuum leak which causes the engine to run lean and ping. Usually tightening the bolts to spec is enough, but occasionally the gasket needs to be replaced. This is common enough, that I periodically (once or twice a year) go out and torque these bolts as preventive maintenance.

There you go, the most common fixes, in no particular order, and it may take a combination of the four. None is real expensive or difficult. Try those and see if your problem is fixed. If not, come back and we'll see what else we can come up with.