I've dealt with this issue before on my 98 Ranger 2.5L and our 93 Ranger 2.3L. My 98 is what is bothering me. It's got 186,000 well cared for miles and the spark knock is happening a lot more. I use to have a Superchip installed and ran 93 Octane, and the spark knock wasn't as bad, but it still did it at WOT. Now that I removed the chip and changed back to 87 it does it most all of the time 50mph and above. It can't be an ignition problem anymore if it ever was. At 180,000 miles I installed 8 SP432 Motorcraft Platinum plugs, which had the same long part number listed on my VECI label under the hood. I also installed a set of Accel Superstock Spiral Core wires. The coil packs are Accel Super Stock Ford EDIS Coils. It wasn't as bad after I did the tune-up and the Super Chip was still installed and still running 93 octane. The chip was removed because it again kept throwing random computer errors up. It needs to be replaced again. This will be the second time I've replaced the Superchip. I've talked with other Ford Ranger owners who had the same spark knock problem even with 3.0s and most of them said the computer had to be replaced to remedy it. Is it time for a computer replacement on mine? Could it cause excessive spark knock? Nothing else has happened or is wrong with this 98 2.5L which has 186,000 miles, it still gets 22-24 MPG in the city. Of course 300 miles after the warranty is up the 4R44E Automatic has started slipping again in 2nd. Other than the worst automatic transmission ever made, this Ranger has been a really good truck. And That was a remanufactured Motorcraft transmission from the Ford Dealer, or so they say it was remanufactured. Could the slipping be another indicator of computer malfunctions? I doubt it on that, but what do you suggest?

 

Welcome to FTE.

Well if you have the stock computer chip back in it & it's still pinging on 93 octane, you could have combustion chamber carbon deposits, causing hot spots.

These engines aren't desiged to operate on high octane fuel & our owners manual says it's use, over prolonged time, can cause engine deposits & driveability problems, but at 186K I suppose it's earned the right to have a few deposits!!!! lol

If you think carbon deposits are the problem, try running most of the present tank of gas out, add a bottle of Chevron "Techron Concentrate Plus" at the specified per gallon treat rate, refill the tank with Chevron or Chevron/Texaco fuel & drive most of the treated gas out, with some spirited interstate runs & daily rpm above 3K rpm, for two or three miles, to remove those deposits.

Also be sure you have the Ford specified heat range spark plugs installed.

Another possibility is a dirty MAF sensor. So check it & if dirty, pull it to clean with spray "throttle body" cleaner, then check up stream in the air box & see why dirty air is getting to the MAF.
Typical problems are a mis fitting air filter, over oiled, foam or gauze type air filter, air box not properly buttoned up.

Just some thoughts for consideration.
Let us know what you find.

 

I've always added a bottle of fuel injector cleaner each 3,000 miles when I change the oil. It's not always been Chevron brand, usually the cheapest brand, since they contail the same chemicals. The oil never gets to stay in the engine anymore than 3,000-3,500 miles. I always use a quality brand oil, usually Shell 5W30 or Motorcraft 5W30, and there's never been any other oil filter on except Motorcraft FL400S. I'm actually running 87 octane, with no Superchip installed. I took the Superchip off because I thought it was bad again, but it turned out to be loose/corroded battery cables. But I will leave the Superchip off anyway since of course my transmission is slipping again. When I did the 180,000 mile tune-up I tried some of the Seafoam Injector cleaner run through the Brake Booster Hose. Just about the amount it said, 1/3 pint. That really cleaned the combustion chamber out good, and improved performance and mileage by 1 point for awhile, and reduced rough idling. I have replaced the MAF sensor, since I thought it was causing a rough idling problem. Which it seemed to clear it up a bit, but now it's just because of the open element conical air intake kit, I've had on there forever. The Seafoam is basically like the shop injector service but without using a vacuum bottle, you just pour small amounts at a time, plug the hose up and idle it partway, and it blows all the carbon out the pipes. The Motorcraft plugs I've put in, were the same number the truck came with new. If I have to guess, it's deposits from all the time running 93 Octane when the Superchip was installed. But it's nothing to tear down the motor about. Although our 93 Ranger 2.3 does the same thing and it's never had a modification at all. It's got 220,000 on it and starts up with the slightest turn of the key, no matter how long it's been sitting. It's like Christine, I think it's got a soul!