I have a '98 with a 4.6. A few weeks ago I was driving my truck when I started hearing this chatter noise coming from the engine, especially under load. It wasn't loud, but it was noticable. I usually run 87 octane gas. When I refueled, I filled up with 92 octane. The chatter was gone. I thought maybe I had bad gas. So I went to another gas station the other day and filled up with 87 octane. I the truck ran fine the first half of the tank, but the second half of the tank I started hearing the chatter again. Not as bad this time. So I filled up with 89 octane and everything seems to be good.

Does this sound familiar to anybody? What does it sound like? Is it detenation? just bad gas? Is it severely hurting my engine?

Thanks in advance.

 

That sounds very familiar. Unfortunately I don' know what it is. I use to always use 87 octane until I heard the noise in my engine. I completely laid off the cheap gasoline and my engine is noise free. From time to time I do use the cheaper gas and the noise comes back.

 

Sorry to hear that. You have now joined the "4.6 pinger club". Pinging is the noise you hear, moreover preignition cause by carbon builup in the combustion chamber. My buddy had the same problem as you, as do alot of other 4.6 owners on this board. We fixed my buddies with some stuff called "seafoam" you can get it at a marine supply house. It removes carbon and you suck it into the intake thru a vacuum hose directly out of the can. It smokes while its being used but stops after that, its o2 and cat safe. worked for my friend.

 

I have experienced the same knock/ping in a 98 4.2l at 27 k miles. Goes away when I use premium gas instead of regular. I have tried techron treatments and octane boosters to no avail. My mechanic says engine and egr are fine. That leaves mass air flow or knock sensor. Since gas mileage is good and engine is smooth except under load at about 2000-2500 rpm it must be carbon still or a knock sensor. I'll try that sea foam before a new knock sensor. Sure hope some of the experts on this forum can give us some answers.... Anyone know where a knock sensor is located?? Thanks

 

So if its preignition cause by carbon builup in the combustion chamber, why does higher octane gas stop the pinging? Will the pinging hurt anything, or do I need to do something about it now? How serious is it?

Thanks

 

The higher octane gas stops the pinging because it burns slower, thus eliminating the predetonation. Most will agree that pinging is bad for the engine, but to varying degrees. I "try" not to let any of my engines ping because it probably isn't good, but I've got a 2.3L turbocharge 4 cyl in a Thunderbird that has pinged forever regardless what gas I run and it still runs great at 115,00 miles.

 

Detonation is not a good thing. It may be tolerable to some drivers, but not this one.
If the cause is carbon buildup on the piston, that will rob power and gas mileage.
If the cause is bad gas... changing gas should solve it.
If it is experienced only under load at a certain rpm then timing is off(too far advanced) and should be corrected. That is where the "knock sensor" comes in. Replacing that should solve that problem.

But as we both have found out , just running premium gas stops it too. Because it burns slower and cooler.

Anybody know where the knock sensor is located???