pings and knocks

[98SableGS]

I have a 1998 Mercury Sable GS 3.0L V-6. When I drive up a hill the motor pings and knocks. Could this be a knock sensor. The check engine light is NOT on for any code. What could it be. I have done a tune up on it with no positive results. Thanks for your answers.

[DistanceGuy1]

Here are some thoughts for you:

Using gas with a low octane rating can cause knocking. Always use the octane rating recommended by the vehicle manufacturer. With gas prices increasing, many owners have switched to a lower octane fuel in order to save money.

In addition, anything that increases combustion chamber temperature can cause knocking such as failure of the EGR, a cooling system problem, burning engine oil, or incorrect spark plug heat range.

A too lean condition, such as a PCM, fuel system or a vacuum leak problem, can also cause knocking.

On an older vehicle, especially one used primarily for stop-and-go driving, deposits can build up in the combustion chamber leading to the hot spots that cause knocking.

[98SableGS]

Thanks for all of the information. The check engine light came on the other day P1131. So I think that means I have a vaccum leak.

[DistanceGuy1]

I copied this for you from someone else asking about the very same code...the response is from a Ford mechanic...appears to be worth reading:

"The sensor is probably reacting to a vacuum leak of some kind, causing that bank to run lean. In this case, it's the bank one, upstream sensor - which is the one at the back of the engine, between the manifold and the cat. Often, air or vacuum leaks in the air intake, or a faulty MAF, will cause a lean code for both banks, but not always, so don't rule those out.

Also, with the engine idling, spray water with a garden hose all around the intake manifold and air lines. If there's a vacuum leak, it will suck in water and cause the engine to stumble. Sometimes, when the leak is bad enough, you can actually hear the slurping noise as the water gets sucked in.

So, check for leaks first, and clean your MAF, and if you don't find any other concerns after cleaning the MAF, disconnect the battery to clear the PCM, and see if the code comes back. I wouldn't replace the sensor yet, as it's not likely the problem. Oh, and I also wouldn't bother to change all the sensors, if one goes bad. Some people say you should replace them every so often, or change them all at once. I don't buy into that, nor have i ever seen anything in print from Ford that says it's true either. Replace the bad one, leave the rest til they go bad, unless you really wanna spend the extra money now. Of course, it's up to you - on your car, that back upstream sensor is really the only hard one to get at, but if you wanna do them all at once and be done with it....."