#GasolineDirectInjection

Dear Sajeev,

I have a 2015 Honda Fit LX manual, purchased new. From day one I noticed a slight momentary hesitation under moderate acceleration when the engine was cold. I took the car to the dealer after a few weeks but they could not duplicate the problem. I dropped it off again and left it overnight, hoping a cold engine would allow them to experience the issue. No luck.

Fast forward 57,000 miles. Same problem persists and is reported to dealer via phone several times. The check engine light comes on. Dealer says the code means an #3 cylinder misfire. They say the fuel injectors are clogged and charge $1,300 to replace all four injectors. Honda of America throws in $1,000 of goodwill money because fuel injectors are not covered by the 60,000 mile powertrain warranty.

Two weeks later light comes back on. Same code. This time another dealer pulls the head and finds carbon buildup on all four piston heads. They clean up the engine, clean the throttle body and declare the vehicle fixed. Total charges paid for by Honda of America under goodwill claim except $217 for the throttle body cleaning. That was yesterday and I will know within days if the original problem persist.

Tech rep was awesome. He recommends I get the fuel injectors and throttle body cleaned every 30,000 miles. My question, what caused the carbon buildup? Does the buildup damage the engine even if later cleaned up? Should I dump the Fit? It is an awesome commuter. I average 44 mpg summer and 39 winter.

Brian writes:

Hi Sajeev,

You are my go-to guy for in-depth automotive knowledge. (Wow! Honored. – SM)

My brother has been having a heck of a time with his 2012 Mazda3 Skyactiv. It’s got about 70k miles on it, and in the past 2 years it’s been in and out of the shop. It started with high engine oil consumption (more than a quart per 3k miles, and going up to this day). Then the ignition coils needed to be replaced. Then the MAF and oxygen sensors needed to be replaced. Right after those were fixed, he had to take it back to the shop because there is now a misfire in one of the cylinders.

What’s going on here? My only guesses are worn piston rings causing engine oil to run into the combustion chamber (then down the exhaust and ruining the O2 sensor), or malfunctioning PCV, a broken EGR system, intake valves with a lot of carbon deposits, or simply “bad luck” with this car.

Hope you are able to shed some light on this mystery. Thanks!

TUV Nord, a safety testing and certification agency, has issued a report commissioned by an environmental group that says that modern engines that use gasoline direct injection (GDI) of fuel emit more small particles in their exhausts than modern diesel engines. Particulates raise concerns over possibly causing cancer. GDI has proliferated as a means of increasing power, improving fuel efficiency and lowering CO2 emmissions but TUV Nord says that GDI engines put out 1,000 times more harmful particles than traditional gasoline engines and 10 times more than the latest diesels. The study is based on a sample size of three cars, a Ford Focus with a 1 liter EcoBoost engine, a Renault Megane with a 1.2 liter Energy TCe, and a Hyundai i40 with a 1.6 liter GDI engine.

“The cost of a filter to eliminate particle emissions from GDI cars is low (around EUR50 [~$68 US]), with no loss in fuel efficiency and a big societal benefit. Despite this, carmakers are delaying fitting filters on GDI cars,” the Transport & Environment advocacy group based in Brussels said in a summary of the report.

“Ask an Engineer” is hosted by Andrew Bell, a mechanical engineer and car enthusiast. Andrew has his MASc in Mechanical Engineering from the University of Toronto, and has worked on Formula SAE teams, as well as alternative fuel technologies in Denmark and Canada. Andrew’s column will explore engineering topics in the most accessible manner possible.