Oil change Cures Knock!?!

[Stardust]

I'm a noob here so if this is a dumb question............well
I've got an '01 Ranger with the 4.0 V6. A while back it started to ''ping'' under light to heavy acceleration. Funny thing though it only starts at about 2300 to 2500+ rpm. I tried new plugs, varying gaps, SeaFoam treatments (de-carbon), cleaned the MAF sensor all with minimal results. The ping got so bad I thought I might bust a ring groove or whatever damage one might get from excessive ping. Not being the type to take my ride to a dealer$hip I started to just park it and take a head off to see if the piston tops and combustion chambers were carboned up.
Well it just so happened it was time for an oil change. After new oil (and filter).......NO PING!!?? None. WTF??

I just plain don't understand what's going on.

Oh yeah, after about a 1000 miles the ping is starting to come back!! Same RPM range but for now really mild and not all the time but I think it's probably going to get worse.

I'm really hoping you guys can tell me what's going on and how to fix it.

Stumped
Stardust

 

[Big Jim M]

There are a lot of things that add to the causing of a ping.. Air pressure, humidity, amount of H2O in the air.. Then the gasoline might add to the ping from tank to tank. It would be rare indeed that an oil change would stop a ping all by itself.
Ping is caused by too much timing advance, which at your RPM indicated is all in at that time.. OR too little fuel mixed with the amount of air ( a LEAN condition).. Or too much compression such as carbon build-up on top of the pistons..
Big JIm

 

[Stardust]

Yep I have to agree with you Big Jim. But I kid you not it stopped completely. The ping was a constant from tank to tank and all kinds of weather. Even high octane gas helped but very little.
It makes absolutely no sense! I've been a "shadetree'' mechanic for most of my 55 years and I'm baffled.

And yes when one thinks of ping or pre-ignition it's usually too much advance, too high compression, too low of an octane fuel or carbon causing excess compression or hot spots.

I must be missing something.............................

Thanks for the reply.

 

[DeanMLFlame]

my 91 4.0 does that but it's only when going uphill and around 1800 to 2300 rpm...in the original service manual that came with the truck it said it would do that occasionally but i didn't say why...

 

[0ldman]

Sure its not running warmer with thin, old oil?

 

[F150hybred]

I have been fighting the same thing also. You might want to keep an eye on my post for a POSSIBLE conclusion. http://www.therangerstation.com/forums/showthread.php?t=23229

 

[MAKG]

IF the oil is fouled or broken down, it might cause a ping. Are you consuming the oil as well? Oil is a significant octane reducer.

You might try putting some Mobil 1 in and seeing if that changes anything. Conventional and synthetic oils don't burn in the same way.

 

[JohnPi]

What kind of gas mileage are you getting?

I'm wondering if there is some sort of leakage of fuel to the oil, doing what MAKG is suggesting (fouling the oil), that might compromise the cooling and lubrication properties of the oil. That might explain hot spots that could cause detonation. Does the oil smell funny?