1999 Grand Marquis pings or knocks

[ortizmro]

I have a 1999 Grand Marquis LS, 4.6L V8, with about 57,400 miles on it. I use the recommended 87 octane gas.

Problem is, after the car warms up, it makes a noticeable pinging or knocking noise when accelerating lightly. Worse on a hot day, but it does it on cold and hot days once the car itself is warmed up. If I accelerate hard, it doesn't seem to make the pinging or knocking noise at all (or I just don't notice it).

Two years ago I noticed this same problem for the first time, and I took it to a Ford service shop and they "de-carboned" the engine. The problem went away for awhile, but it is back. The service advisor warned me that it would come back eventually. Before they de-carboned the engine, they had me try a fuel additive called 44K, which had no impact at all.

Otherwise, the car runs real smooth. I do not drive it very much or very far. I put maybe 8,000 miles a year on the car, doing mostly city driving.

I have been tempted to try a higher octane gas, but the Ford service advisor strongly advises me to NOT do that.

Anyone have recommendations?

Thanks in advance....

[weekender1]

i have the same problem. tried an injector cleaner that i added to the gas tank. it made a small difference, but the noise was still there. I tried a 10w30 oil but the noise got worse so back to the recomended 5w30.
it only occurs when im accelerating lightly while the trans is in a higher gear. once the trans downshifts, no problem. seems to me it's a question of driving style. this engine does not like to torque its way around town, but to be stepped on. just an opinion.

[fredjacksonsan]

Depends on the noise. If it's a very very light tapping, that's normal for an engine that is running lean (the way it's designed to do at light acceleration) Once you give more gas, the computer puts it to a more aggressive profile and more gas so the knocking goes away. If you get into a heavy knocking, that's not good. Does it sound like a diesel truck or just a light tapping sound?

[ortizmro]

Originally Posted by fredjacksonsan

Depends on the noise. If it's a very very light tapping, that's normal for an engine that is running lean (the way it's designed to do at light acceleration) Once you give more gas, the computer puts it to a more aggressive profile and more gas so the knocking goes away. If you get into a heavy knocking, that's not good. Does it sound like a diesel truck or just a light tapping sound?

It is not heavy at all. And happens more when I am lightly accelerating. Heavy accelerating never produces this sound. I would just like to know that it is not damaging to the engine. If it is "normal," then I will quit worring about it.

[fredjacksonsan]

Hopefully it turns out to be normal. : ) If not, you can go by my brother's creedo: "Drive it until it explodes!"

[ksaman2004]

Try to change the spark plug cables and coils. I had the same problem in my GM 97, but after I did that the noise goes away.
Hope this will help

[James Hurlburt]

could be one of two things.
Check the EGR passage in the thottle body for carbon buildup.
Also check the MAF sensor. Unplug it and take it for a ride

[WickedSix]

Sounds like the MAF sensor is dirty, might wanna clean the wires and reset the computer.