1999 Grand Marquis pinging

[rtf4286733]

I have a 1999 Mecury Grand Marquis, 79 K. Light knocking /ping upon shifting into fourth gear , seem to happen once car is fully warmed up. Gradual acceleration no pinging, too the floor sounds like marbles. I did scan, no error code, all passed on obd 2. Decided to read / change plugs - all 7 looked light tan, normal, cyl # 8 cyl last bank right in front of driver- had lightcarbon build. Different than other cylinder. Replaced plugs & put in fuel injection cleaner. No difference. Initially suspected MAF or O2 sensor, but wouldn't that fail on scanner? No error codes, no check engine light. I'm leaning towards this #8 cylinder -- Intermittent coil opening @ hot temp, or drop in voltage? Plugged fuel injector for # 8 ? Also I've read that light pinging is normal for this vehicle. Please help, you thoughts, or ideas or experience with this would be greatly appreciated.

[way2old]

Does your scan tool read the sensor data? If it does, look at the baro on the vehicle. It is read in hertz and varies depending on altitude. We are at about 1000 feet and our reading should be around 156 hz. If you are reading a real low number, try cleaning the MAF and see if it helps.

[Roel1987]

Hey, I Have A 1997 Mgm With A Similar Problem, My Car Would Be Quiet When In Park. But When Trying To Pass Another Vehicle It Would Rattle Like My Engine Was About To Break!!! I Tried Using Higher Octane Gas And No Success. Finally I Took The Maf Sensor Apart And Cleaned It Real Good With Electrical Cleaner(4.99@autozone). And Booooom!!! Worked Like Brand New Marquis... I Also Noticed Alot Of Gain In Horsepower. I Guess It Just The Original Hp Got Back.

[callenmc]

I have been having this pinging problem with my 1999 Grand Marquis which I have 99,000 miles on the car. I have had Hyper Tech tunning on it since 10,000 miles. Car also would ping very bad under load and high rpm's. It seem to be better and sometimes no pinging at all when it would rain or heavy dew. No engine lights or codes. I also thought of the Massive Airflow Sensor. I finally pulled it out and cleaned it with carb cleaner, then thought, I shouldn't of used carb cleaner. Looked on line and found I shouldn't of used it. Took sensor back out and cleaned with electronic cleaner. Yes this solved the problem. No more pinging!!!!!!!