Some things to check on pinging Ranger 3.0 engines. The 3.0 Vulcan Flex-fuel engine is very prone to pinging. They are set up to run on up to 85% ethanol, so they have more advance, a bit more compression, and the chambers tend to carbon up.
•Buy a service manual
•Check for vacuum leaks. Hoses, and the intake manifold gaskets.
•Sea foam the engine. Be careful- feed it in too fast and you can seriously damage the engine. Go in through the vacuum port just behind the idle solenoid. Get a friend to keep revs at about 1500, feed in just enough to make it run rough. Suck in about 2/3 can, shut it down and let it sit about 20 minutes. Start it up, feed in the rest of the can, hook the vacuum line back up and go for a hard drive. It will smoke like hell, if you have sensitive neighbors, do it out on a back road someplace.
•Check the EGR valve, make sure it is operating smoothly. You can apply a little vacuum to the EGR valve, it should open easily and the engine will almost stall.
•Check the metal EGR tube- mine had a huge split in it. Check the 2 pieces of silicon tubing that go from the EGR tube to the DPFE sensor, they sometimes get plugged. Do not use vacuum tubing, this is high temperature stuff. Find a dealer that buys it bulk, the individual tubes from Ford are stupid expensive.
•The old DPFE sensors have a habit of going bad. It measures the flow through the EGR tube by pressure drop through an orifice. Check the input and output voltage. I forget what it should be, it’s in the manual.
•By-pass the hot water going through the intake manifold. Sometimes helps.
•Run colder spark plugs. Original factory plugs were a #AGSF32 (not sure of the letters), later they went to #22, some people have gone down to #12. I am currently running AR-93, Autolite racing, 2 steps colder than stock.
•I know this will cause some arguments, but after all the above, my truck still pings a bit on some brands of 87 octane, does not on others. If I am not sure of a particular brand, I just put in the 89. Ten cents a gallon is a lot cheaper than engine parts. I do not get hung up on running 87 octane just because "the manual says ...". I run whatever works best in my vehicles. 6 vehicles with well over 200,000 miles tells me I'm doing something right.