F350 460 pinging under load
 

F350 460 auto 1992 dually 2WD 120 K miles.
My cat is half empty as half the honeycomb inside was broken and the exhaust system was whistling. Could not rev more than 1200 rpm without whistling. Cleaned the inside of the cat and now no more whistle. Engine runs better but pings under load at about 1800 rpm. Could the pinging be cat related ? I dont know if last time I fueled I took regular gas (87) or premium. I will check all vacuums.
What else should I check ?

Timing sounds to be off a bit

An engine is nothing more than a big air pump. You removed a restriction from the system, by cleaning out the cat, and now you can move more air through your engine. The problem is that the EFI isn't compensating for that extra air flow. My first thought would be the Speed Density type of EFI you have just can't keep up but there are tons of folks that put headers and free flowing exhaust on their trucks without issue. Maybe someone will chime in with more on this. This leads me to think you may have a sensor that may be telling you truck something wrong. Think O2, water temp, Air temp (does SD have air temp?), etc.

I don't know everything about EFI 460s, but I've learned a lot since I bought mine a few years ago. This could be something simple. Bad gas, bad plugs, timing a little off like stated above, high water temp, vacuum leak, etc.

I would check the timing first, and then I would check to see if there were any stored codes...

You said your cat died which could have been from excessive heat from a lean condition. I had a vacuum cap fall off the tree below the throttle barrel that would make the truck ping up hill but idle fine because it was such a small vent. Timing wont suddenly go off unless it has been pinging for longer than you knew. By the way I always run reg fuel with no detonation.

update to F350 460 pinging under load
 

Thank you guys for your input. Vacuums in engine compartment seem OK. There was a leak caused by rust in one of the two steel pipes on top of the catalytic converter. I repaired that but cannot put the truck under load before a few days. I am not sure it will make a difference. Meanwhile, I will try to pull the codes, first time I do that. I found the procedure on a post by conansky who refers to Ford Fuel Injection. As for checking and ajusting timing, I dont know yet how to do it, but I will find.
I want to keep that beauty as long as possible, so do you think I should find a Haynes manual or other reference ? All i have now is the Ford Service Manual on CD and I dont find it very practical.

Check for proper EGR function?

Yeah, get yourself a Haynes manual. I have one for every vehicle I have ever owned. It's one of the first things I do when I buy something new. They lack some detail but are a great over all reference. And your CD can fill in any gaps that you need.