this is in reference to my 97 F250 LD....4.6....i just had my truck tuned up due to rough idling and some knocking....the mechanic changed the plugs, cleaned the EGR ports....right after this was done a code popped up....after taking it back the mechanic said the left rear plug wire was bad....the one that collects moisture due to bad design....he said the contact point at the plug was a little rusty but managed to clean it up w/compressed air and dilectric grease.....this fixed the poor running condition, but it still knocks under load, especially when pulling my jon boat which isn't that heavy.....any thoughts??? can that plug wire cause the knock??

 

Possible, but not probable. I would say that you probably have some carbon built up in the cylinders.
You can try cleaning the Mass-Air sensor first. If it is dirty, it will not properly measurew airflow and can make it run too lean causing pinging.
A good injector cleaning probably wouldn't hurt either.
Jimmy

 

is there any fix for the carbon buildup?? this symptom only pops up when the truck is good and warmed up too....

 

There is the possibility that your EGR system isn't functioning correctly, even if the ports were cleaned out. My 4.6 did the same thing until I cleaned the ports myself, and changed the non-working parts of the EGR system.
Here is my reasoning: EGR is designed to reduce emissions by reducing maximim temps within the cylinder when it fires. Without EGR gasses, temps rise to the point that the fuel-air mixture detonates rather than burns smoothly. This detonation, which sounds like marbles rattling around in a can, is called pinging. Pinging is a classic symptom of no/poor EGR function, a too lean condition, or of carbon buildup in the cylinder. This will be worse, by the way, when using higher octane fuel.
When considering the highly tuned state of these computerized engines, the need for proper operation of the EGR system becomes even more critical. So, the first thing I would check is the EGR system.
Are you still getting MIL or CEL code indicators?
If so, you probably need to clean out the orifice tube, or re-clean the EGR passage in the throttle body, replace the DPFE (Differential Pressure Feedback) sensor and or the EGR valve or solenoid.
On my 4.6 with 98K, I had to replace all the sensors, the EGR valve, clean the orifice tube, and clean the EGR ports. It wasn't hard, and I did all that work in about an hour, even though I had never worked on a Triton motor before.
My mileage went up too, from 12 to 18 mpg.