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The vehicle is a 1997 F150 4.6 Auto 4X4. At highway speeds, it wants to spark knock pretty consistently when the engine is under a load. Third gear climbing hills is the worst, and even overdrive cruising up moderate hills is bad too. It seems to only want to do it over 2300 RPMS. I am getting good fuel mileage, well, normal fuel mileage. I haven't seemed to have lost any power. When I use premium fuel it seems to help quite a bit. I have heard that 3 probable causes are knock sensor, mass air flow sensor, or carboned up engine. I have tested the Mass Airflow Sensor with a multimeter and it tested perfect. I have been running injector cleaner such as Seafoam and Techron quite a bit lately, so I don't think its a dirty engine. I have been told that the knock sensor is located in the middle of the valley, under the intake manifold. What else could it be? I want to rule out all I can before I take the top of the engine apart. I have no check engine light and no trouble codes.
I finally took the truck to Ford to have them try to fix it. They cleaned the maf sensor(which I already have done), and they reflashed the computer($238 total). It helped quite a bit, but didn't totally stop the pinging. The only time it pings now is when your in 3 gear (auto) and climbing a big hill going 65+ mph. I can pretty much tolerate that amount of pinging. The truck climbs hills in overdrive fairly well, so it shouldn't be too much of an issue. Hopefully it doesn't go back to its old ways eventually.
I have the same issue now. I posted a bunch of times on my header change...everything else is resolved. Now I am down to the knocking while speeding up while going up hills.
Do you have anymore to add to the thread? All suggestions are appreciated.
Well the truck slowly went back to its old ways. I have been pulling the appropriate fuse to reset the KAM about once a month. I have been putting premium in it when I pull a trailer and that stops all pinging. Still pings when in 3rd gear above 2500 rpm on 87octane. May return to ford eventually.
I found a vacuum leak. I hate to say that I am not sure what it is called. Its the black tube that is in the shape of a 45 deg bend. It is the same size as a 3/4" heater hose. On the 4.6 it goes from a black box to an inlet right by the idle air control. Replacing that got rid of the pinging that was really bad going up hills. But I still have that knock like yours. I have heard sea foam is something to try if you think its from a carbonbuild up. I have plans to try that before the knock sensor replacement.
Thanks for keeping this up to date.