99 Explorer knocking

I have a 99 Explorer. Ever since I've got it, it has that"pre-ignition firing"
(I think that's what it's called), and on regular gas, which I use all the time(can't afford high test anymore!) when you go uphill or accelerate, you hear it kinda knocking . The dealership said it didn't hurt anything, and to try mid grade or high test. Has anyone else experienced that??
Also, how are the tranny's in the 99's? I've heard some horror stories.
I only have 56,000mi on this truck.
Thanks!

Is it a knock or sound like valves clanking around ? Try at least the midgrade to see if it helps.

Is it a knock or sound like valves clanking around ? Try at least the midgrade to see if it helps.


I have tried midgrade,but not more than 1 tank full. Saw no difference.
It's more like a knocking sound.

Try the premium see if it goes away. Usually only a "pinging" will happen with the fuel thing. A knock might be something else. How much for premium there? I pay about 1.65 that's all my car takes.

The knocking or pinging sound is when I accelerate. If it is the gas, does it hurt anything ??

Pinging occurs when the fuel is ignited before it's supposed to. My car takes premium fuel only. My Wife has a 01 Mercury Moutaineer although it doesn't require premuim we run it to make the pinging stop.

I have a 1994 with a 4.0 engine. I also have the same problem and have tried everything. The dealer said they can't repair it without tearing the engine down. The timimg can't be set I'm told.

I bought my car off the lot with 8 miles on it. I have since performed every routine maintenance on time. I've had nothing but problems since the day I bought it. It makes this humming sound, that was finally determined to be the idle air control valve, only replacing it doesn't fix the problem. I replaced the tranny when it was 2 years old. The motor that opperates the windshield wiper fluid stopped working within the first year. The CD player won't take CD's- it ticks and spits them back out. The driver side window came unglued from the track and had to be replaced. It makes that knocking sound you were talking about. The back windshield wiper won't even wipe. Something was wrong with the regulator on the engine coolant cap, my car overheated on a 110 degree day in July, and since it was so hot outside, it exploded the coolant system and the whole thing had to be replaced. I'm sure I'm not thinking of everything, but isn't that enough? Four more payments, and that piece of ish is out the door, and I will DIE before I ever own another Ford. Oh yeah, and now my check engine light is on, only when you check the engine it detects no problems. Oh and it was quite insulting to find out when I had a sripped drain plug that the ONLY place you could buy a new one was at Ford, and it costs $15. FOR A DRAIN PLUG!

I have a 99 limited explorer and the fuel injectors are rated for premium fuel only. Anything less, and I get pinging.

Not sure if this applies to your vehicles but some Fords do have a "octane adjustment" built in to the engine electronics. As far as I know this is a dealer thing involving re flashing the ECM.