Piston Slap: Start With Spark Plugs!

Sajeev Mehta
by Sajeev Mehta
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.

Sajeev answers:

What codes did you get with a scanner?

Supaman replies:

Haven’t scanned the codes because more often than not the CEL light doesn’t trigger.

Sajeev answers:

There’s a (remote?) chance that an intermittent code isn’t triggering the light. So scan now.

Supaman replies:

Hey Sajeev,

Took matters into my own hands and decided to throw some new parts at the Mazda. I bought new spark plugs and ignition coils and decided to dedicate a Saturday to replacing them. What was supposed to have been a three-hour job turned into eight hours of wrenching, ughing, cursing, awkward body positioning, pulling and beer (yes, beer lol).

Anyway, inspecting the forward bank of spark plugs, I found oil coating the middle plug (see pic). The forward left plug was clean (save for carbon deposits I suppose) while the forward right plug had just a hint of oil on it. This (along with the many forums I looked up) tells me my valve cover gasket is bad. I was able to use a clean cloth and mop up as much oil as I could before placing new plugs and coils into the forward bank. Apparently, the leak was so bad it made it up to the coil itself at some point.

The rear bank of plugs were clean, except for signs of normal wear. After buttoning everything up and taking it for a test drive, the hesitation and stuttering are gone and she drives as great as she did 20,000 miles ago. While at it, I cleaned the throttle body, replaced the intake port gaskets, and cleaned the EGR valve and MAF sensor. Of course I know this is a temporary fix and I’ll have to replace the valve cover gasket, hopefully sooner rather than later. Just wanted to give you a heads up and to anyone that works on their car, believe me, it’s a money saver.

Total cost in parts? $95. Total labor? 8 hours on a Saturday and a six-pack of stout. Thanks again!

Sajeev concludes:

I did a similar job to a Duratec Sable with well over 200,000 miles. While the plugs were toast and the EGR was coked up to near complete blockage, the motor still ran reasonably well. A good cleaning and new plugs were all it needed: odds are your coils were fine, just like mine were.

Working on wrong-wheel drive cars with bulky DOHC V6 engines is no fun, but the basics? The basics gotta be done.

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.


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  • Speedlaw Speedlaw on Dec 11, 2014

    I've learned to replace plugs at the 60k interval, no matter what the book says. I had bad coils in my MDX, dealer said "if it doesn't toss a check engine light it doesn't exist". I replaced the coils and plugs, and "poof'....perfect idle. Two trips to the dealer with "all is working properly", to boot. Thanks guys. (really, you fix five cars and can't get this right ?) Plugs are a lot like o2 sensors. Over time they degrade, but don't activate a check engine...and usually so slowly you don't notice day to day. Only when you replace them you discover the fifteen horses hiding in the corner of the barn.

  • SupaMan SupaMan on Dec 15, 2014

    The car is nearly 110k and the engine is still purring smoothly. I'm wondering whether or not I should even bother changing the other gaskets like I said I would but I guess prevention is better than cure. Thanks again Sajeev!

  • Jeff S This would be a good commuter vehicle especially for those working in a large metropolitan area. The only thing is that by the time you put airbags, backup cameras, and a few of the other required safety features this car would no longer be simple and the price would be not much cheaper than a subcompact. I like the idea but I doubt a car like this would get marketed in anyplace besides Europe and the 3rd World.
  • ScarecrowRepair That's what I came to say!
  • Inside Looking Out " the plastic reinforced with cotton waste used on select garbage vehicles assembled by the Soviet Union. "Wrong. The car you are talking about was the product German engineering, East German. It's name was Trabant.
  • Inside Looking Out To me it looks like French version of Hummer. The difference is that while American Hummer projects power French little Oli projects weakness.That vehicle reflects the bleak future for EU. For now they have to survive coming winter but in general population collapse it coming soon, Europeans will be gone in the long run. Only artifacts like this concept and legends will remind us about advanced and proud civilization that populated that small continent the civilization that in the end lacked will to exist.
  • Conundrum "the plastic reinforced with cotton waste used on select garbage vehicles assembled by the Soviet Union." Nah, wrong. But it's Posky, so should I be surprised? That body material, Duroplast, was invented by Germans, used on the East German Trabant car and dulled many a saw blade when trying to cut it.https://en.m.wikipedia.org/wiki/DuroplastThe Soviets made regular sheet tin cars. Nothing fancy, they just worked, like Soviet farm tractors you could repair with a pipe wrench and a 14 lb maul. They exported quite a few to Canada in the '60s and '70s and people used to swear by them.I suppose this new Citroen Ollie has LED lights. If they fail, does one go to the Dollarama for a $1 flashlight, then rip out and use those LED "bulbs" for a repair?I think this Ollie thing is off the rails. The Citroen 2CV was ingenious, both in chassis and especially suspension design and execution, but where's the innovation in this thing? Processed cardboard panels, when corrugated tin, a Citroen and Junkers favorite fascination would be just fine. Updated with zinc coating from circa 1912 and as used in garbage cans and outdoor wash tubs ever since, the material lasts for decades. Citroen chose not to zinc plate their 2CVs, just as the car industry only discovered the process in the mid 1980s, lagging garbage can manufacturers by three-quarters of acentury, with Japan holding out until the mid '90s. Not many 1995 Accords still around.This Ollie thing is a swing and a complete miss, IMO. Silly for silly's sake, but that's the modern day automotive designer for you. Obsessed with their own brilliance, like BMW and Toyota's crews creating mugs/maws only a catfish could love, then claiming it's for "brand identity" when people take offense at ugly and say so. They right, you wrong. And another thing -- hell, Ford in the 1950s, if not well before, and innumberable Australians found that a visor stuck out from the roof over the windshield keeps the sun out when necessary, but Citroen delivers first class BS that an upright windshield is the solution. And as GM found out in their newly-introduced late 1930s transit buses, flat windshields are bad for reflections, so they actually changed to a rearward slanting windshield.This design reeks of not applying already learned lessons, instead coming up with useless new "ideas" of almost zero merit. But I'm sure they're proud of themselves, and who gives a damn about history, anyway? "We new young whiz kids know better".
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