<!--StartFragment --> I have a 99 Ford Ranger (4cyl 2wd) with a manual transmission. For years I was able to get by with running regular unleaded in it with no issues. Over the last year or two I haven't been able to do it without problems. If I run regular gasoline in it my engine makes a noise that sounds like ping-pong ***** bouncing on a sheet of aluminum when I'm doing around 55-60 in fifth gear. My little four banger doesn't have a lot of juice to it, and that speed is just a little high for fourth gear and a little low for fifth gear. The problem is MUCH more noticeable if there is any kind of an incline (if I'm going up a really steep hill/mountain pass I basically have to slow down into third or fourth gear to keep the truck from making the noise).

I presume that is what is known as "pinging". If I run higher octane gas it is far less noticeable (but still there). I'm coming up on 100K miles on the truck. I recently changed the spark plugs and set them to the proper gap but that didn't really help the problem. So, any ideas what I can do fix the problem? I'd like to be able to run regular unleaded again...

I'm guessing it may have something to do with the oxygen sensor, but I don't really know what the heck I'm talking about and it's just a wild guess on my part (I don't know all that much about cars). Anything else I should be looking at?

 

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Has the fuel filter been replaced, a lean condition due to low fuel pressure could cause this problem.

 

Yup as Ken has suggested a dirty fuel filter can cause low fuel rail pressure & a lean mixture, which would lead to engine "ping".

A dirty MAF sensor can lie to the computer about air flow & cause the computer to get confused about what the engines load really is & cause fuel trim problems.

Combustion chamber carbon deposits can cause "ping" too.

Did you replace the spark pugs with the correct heat range???? Too hot a plug can cause this.

A intake side unmetered vacuum leak can cause problems like this too, so check all your vacuum lines & the PCV hoses & connections for any loose fitting, cracked, split, or disconnected vacuum hoses.

Loose intake manafold fasteners or faulty, leaking intake manafold gaskets are a possibility.

From your description of it coming about slowly over time, being worse on hills & getting better with higher octane fuel, but not changing with new plugs, makes me want to lean more toward the problem being combustion chamber carbon deposits.

So you might try 5-6 tanks of Chevron or Texaco/Chevron gas, with a bottle of Chevrons "Techron Consentrate" in the first tank & run most of that first tank out, before refilling & see how it respondes to that.

A couple of >3000 rpm 3 mile interstate runs would be good, or a 20 mile intestate round trip run, with some high rpm's thrown in will help with carbon removal.

The Techron is very good for cleaning up combustion chamber deposits.

Let us know what you find.

 

Mine does this too ('98 Mazda B2500). I take it on the highway, floor it in 4th gear and run it up to about 80mph, back off to 60, floor it again up to 80, and do that back and forth about 5-6 times and it fixes the problem for a couple of months.