Piston Slap: Start With Spark Plugs!

Done Duratec’d Out? (photo courtesy: Supaman)

TTAC Commentator Supaman writes:

Hi Sajeev,

Haven’t visited TTAC in a while but I’m back! My Mazda 6 has now crossed the 101k mileage marker and all your nuggets of wisdom have helped keep this classic functional and beautiful. However, there’s another problem rearing its head that has plagued even the Mazda forums I’ve visited for a resolution.

It involves the car’s driveability at anything below 3000 rpm. Doesn’t matter whether the engine is just warming up or at operational temperature, the car will hesitate (sometimes violently) in a stuttering/bucking fashion when accelerating from a stop through the gears until I crest that magic 3000 mark on the tach. Out on the highway, passing in top gear is almost impossible because of the engine’s hesitation if revs fall below that number, requiring a downshift to 4th to keep them up. At first I thought my manual skills were to question but then I never started experiencing this issue until around the 87,000 mile mark. It has since gotten worse. Sometimes the bucking is enough to trigger the CEL but then it always goes away after a while.

Browsing the forums I’ve tried everything from cleaning the MAF sensor, fuel injector cleaner, throttle body cleaning as well as replacing the O2 sensor. I’ve narrowed it down to either spark plugs (some forum members replaced theirs but the problem came back hours later), the coils or possibly a vacuum leak. One post I read indicated a potential cylinder misfire. Even Mazda dealers were confounded.

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