My 97' f150 with the 4.6l/auto and 115,000 miles has slowly started to knock and ping under acceleration. This seems to be mostly at temp and hard acceleration like to pass in a short distance by going from 45mph to 65mph. If I use premium fuel, $3 plus/gallon, instead of the lowest grade it seems to mostly go away. Outside temp and humidity do make a minor difference but supprisingly having a good sized load or the trailer doesn't. I'm aware that it is usually carbon deposits pre-igniting in the cylinders but is there a product that effectively gets rid of the carbon deposits or do I live with it until rebuild time? Truck does run very well and I have maintained it well in the 2 years/30,000 miles since I bought it.

 

I had the same problem with my 4.2 (before i rebuilt it). What I did to fix it at the time was change the "Intake runner control valves" there are two of them on the back of the intake. One for each bank. It seemed to fix the problem.

 

Could be your egr valve, the 4.6's tend to ping when it gets clogged.

 

Thanks for the replys. I'll have to check up on the "intake runner control valves". To be honest, mikemonce, I've not heard of them before this. I don't believe its the egr valve since I don't have any codes and I just went thru all the egr check, egr port cleaning after wrongly changing out the dpfe sensor to get rid of the insufficient egr flow code. That was about 8000 miles ago. I usually just apply vacuum to the egr valve at idle and see if stumbles and stalls...is that correct xtrford? If not, what method of checking do you use. Thanks again.

 

That is correct, when the egr valve is opened at idle there should be a noticable stumble in rpms,if this happens your egr is functioning properly. If you already check and cleaned the egr valve and dpfe sensor then you might start looking at either your maf sensor(dirty) or a reflash of your pcm at ford.