97 f250 light duty 4.6...118k.....i've noticed some light knocking in my engine since the weather has turned colder....this did not occur during summer....any thoughts would be appreciated......seems very odd to me....thanks for any help...

 

Go through all your basic maintenance first - at 100k needs plugs, wires, clean MAF & TB, replace fuel filter, PCV Valve, air filter and clean fuel injectors. Check for vacuum leaks.

I have run into a lot of 4.6's that I have reprogrammed the PCM and that eliminated the spark knock but you have to get the maintenance done first if it hasnt been done yet.

 

Try doing a search on piston slap, although this problem occures more in the 5.4l and 6.8l v10 I do believe it happens ever so often in the 4.6's. Does it go away a short time after you start it?

 

Along with the tune ccoram is reccomending use SeaFoam in the engine to clear away the deposites in the engine. you can add it to the tank but best results happens when you run the engine remove the pcv valve stick the pcv hose into the sea foam can and suck up about 1/3 of the can, shut off the engien wait for about 30 min then restart. It will smoke like crazy (white) for about thirty min go for a drive until it clears up. You will see a vast improvement, At least I did on my 4.6.

Lance

 

Yeah I forgot to mention something along those lines - I've had really good luck with Mighty Intake System cleaner. You spray it into a vacuum port while the engine is running and it de-carbons the engine. Same basic principle as the Seafoam.

 

i've heard of this Seafoam stuff....pretty easy to find?? also forgot to mention that it only happens once the engine is warmed to operating temp.....i cleaned the MAF about 18 mos ago....probly start there and do the "decarboning" as well.....thx....i assume the carbon buildup on the piston tops causes excess heat due to higher compression, thus the knock??

 

roger that, you are correct.Lets hope that is all the problem is.