Ford Ranger / B-Series :: 4.0L Engine Knock - Tried Diff Additives But Nothing?

I too had this problem and tried different gas, gas additives, meticulously inspecting the cooling system to make sure overheating was impossible, found the jumper that allows me to back off timing 2 degrees, checked the computer for error codes, and cleaning the MAF sensor. Nothing really worked.

The solution is to decarbon the engine. It is all described in TSB 01-19-7, dated OCT 01. I did this and END of the problem. Pay attention to the part about not ingesting the PM-3 cleaner too fast to make sure you don't liquid lock your engine. The only important step they forgot was that you will need to replace spark plugs when you're done. You may also want to lay some newspaper under your tailpipe too, as the crud is gonna flow.

The TSB notes that the driver should have "periods of daily operation over 3500RPM to break carbon from cyl heads". They also note that you should NOT use mid-grade or super duper unleaded, as these increase the probability of carbon buildup.

This repair will cost about $30 if you do it yourself; if you can change a flat tire you can do this.