I have an 07 4.2L 5 speed and the spark/labor knock is really driving me insane! I had a Ranger years ago that done the same thing from the time I got it with 40,000 miles and was never able to fix it and when I got rid of it with 220,000 miles it was still spark knocking but running strong. But I think neither should do it.
Here is what it does Under heavy acceleration I have spark knocking and also when I am holding 55-65mph on the HWY the spark knock is really excessive. If have have the cruise set at HWY speeds it is the same thing and if I am climbing an incline it is really bad.
I have no codes pending or otherwise and no check engine light on.
I have tried 93 octane 100% gas with no ethanol and it makes no difference.
I replaced the plugs with Motorcraft OEM replacement and it didn't change. Changed the plug wires put a K&N air filter on and replaced the plugs again but this time used Bosch Platinum +4 and still no change. I also cleaned the MAF sensor.
Other than the spark knock it runs pretty good other than a little bit of a rough idle.
So I am looking for some input on what to check or try changing next.
Also was there a TSB for the 2007 4.2L about spark knocking. I ran across some posts about a 4.2 TSB about spark knocking but I don't think it included my model year.
Its only caused by a couple things. Too much spark advance or excessive carbon in the combustion chambers that glows and causes pre-ignition. I think maybe its carbonned-up which also has the effect of raising the compression ratio. I would start right away using premium gas along with fuel system/injector cleaner in every tank of gas from now on. If this starts to work and the pinging stops, you can drop down to mid-grade and continue the program, finally getting back to regular. At that time I would suggest using a fuel stabilizer/cleaner every time you get gas. The 4.2L in the truck runs rich and you can expect carbon trouble if you don't regularly use an additive.
The low-restriction air filter simply allows more air to pass thru it. The electronic fuel injection system therefore is forced to add more fuel to the air because the MAF sensor is calling for it. The overall ratio of fuel to air is therefore the same - there is simply more fuel/air mixture to burn. The oil treatment on K&N-type low-restriction filters has been known to collect on the wires of the MAF sensor, causing a malfunction. For that reason only, I would suggest using a stock filter at least until you solve the pre-ignition problem.
You'll probably have to use a strong cleaner to reduce the carbon, then a maintenance additive to prevent it from re-forming. For the maintenance additive, I use Sta-Bil for Ethanol fuels, my favorite being the super-concentrated blue which is used at 1 oz to ten gallons. I haven't had to use anything stronger because I haven't had the problem you are experiencing. You might try Seafoam How to use SeaFoam to clean your Engine - The RIGHT way! which is safe and won't harm anything. You really should do the 'injection' method which is explained in the linked article, but I probably would just use it in the fuel where it works all the time. All this is assuming the carbon is actually the problem. It could also be a fault in the engine controls by allowing too much spark advance. In the old days we would get out the timing light and check the timing and adjust it at the distributor. I guess now they have to hook it up and do a diagnostic. Dealers and other shops now also do injection cleaning which is probably a good idea since you're having a severe problem.
Premium fuel is good for this on a temporary basis because it reduces 'ping' and also has more cleaners. I would keep using it and put in a can of Sea-Foam with each fill of 15 gallons or more.
If it doesn't get any better in the first few weeks, you probably should have the diagnostic done to see if there are any control or sensor problems. Most engines have a 'knock sensor' that could go bad and fail to send the signal to retard timing to prevent knock.