Truck Repair: Engine Pinging, ford explorer sport, vacuum leaks

Question
This engine pinging has been driving me nuts Im wondering if you can help
1994 ford explorer sport 4x4 5 spd 119940 miles.
Symtoms: when I push my truck really hard there is a pinging in the engine.
DOesn't happen in first, but around 3k+ in the rpm band in second and third and forth and fifth gear.
I recently replaced the spark plugs and I've replaced the wires too. The engine is being properly cooled I just replaced the radiator.

I heard that if the engine is running too rich or too lean pinging can occur. I noticed a while back that my 02 sensor is loose in its mount, never tightened it. maybe that could be the problem.
My check engine light is on too, I checked the flash codes and it came ot to be something about the egr, never really looked into it further.

I sometimes smell gas fumes whenever its on but no noticeable change in level over time, at least more than is normal.
someone also suggested that it could be weak valve springs but for most of last month it didn't ping at all, after the installation of my cone filter.

Any help you can provide would be great. Thanks in advance.


Answer
Hello Joe,
First of all, why not tighten that o2 sensor. If it needs to be grounded, it could be giving a false reading, which would cause a improper mixture, which could cause pinging.
Then, a vacuum leak can cause pinging. If the EGR valve is not seating closed, it is the same as a vacuum leak. Look for any other possible vacuum leaks also. The installation of the cone filter could have made enough difference to compensate for a leak. Just for jollys, why don't you stick the old filter back in and see if the pinging returns.
I would still service the EGR.
Van