Finding and Fixing One of the Most-Ignored Downsides of Modern GDI Engines

Carbon build-up can destroy an engine. Intake valves get gummed up with build-up, and then nothing works correctly.

Back in the 1980s, it was common for your average family sedans to produce less than 150 horsepower from engines that weren’t all that small. I still can’t believe we drove 3.3-liter Pontiac 6000s making maybe 135 horsepower, and that was good. Technological advancements since then have engines more efficient and powerful. One such piece of tech that’s become ubiquitous is Gasoline Direct Injection, usually called GDI. But it has drawbacks too.

What Is GDI?

Until around 10 years or so ago, most vehicles had port injection. This means that fuel is sprayed in with the air mixture, washes over the valves, and is combusted – creating power. In direct-injected engines, the fuel intake is squirted directly into the combustion chamber. The result is a more complete combustion cycle, using less fuel. Making more power from less fuel allows automakers to use smaller, more efficient engines that still give good performance.

Seems Like a Good Thing, What’s the Problem Here?

Gasoline is caustic, which isn’t always a bad quality. Back in olden times, people used gas to clean dirty metal tools.

In port injected engines gas is continuously washing over the intake valves. This has the effect of cleaning off any build up of carbon, oil, or other contaminants that build up during normal operation. In a direct-injected engine, the backside of the intake valves stays dry, no gas is being washed over the valves. Gas is being directly injected into the combustion chamber, remember? Oil and carbon deposits are still building on the backside of the valves, but there’s no fuel washing all that crap off.

That carbon build-up can destroy an engine. Intake valves get gummed up with build-up, and then nothing works correctly.

How Do I Know if My Car Has GDI?

Finding out if your car has GDI just by looking at the engine is a bit tricky since there’s nothing really visually obvious that’s unique to them. On your vehicle’s plastic engine cover, there may be a big sign that with the letters “GDI,” though. That would be a dead giveaway! Try checking the vehicle’s owner’s manual, too.

If all else fails, a call to the dealership’s parts counter should give you an answer if your car is direct-injected or not. Or, you could always just Google “is make/model direct injected” and you’ll find your way to an official spec sheet eventually once you sidestep a few Quora threads.

How Do You Fix It?

Some automakers have noticed this carbon problem and have attempted to engineer it out. Toyota’s new M-series engines found in the latest Camry and Corolla use both direct and port injection to keep the backside of the valves clean. Oil manufacturers have also added solvents and other chemicals in certain brands to help mitigate build-up, too.

But if and when excess build-up occurs, you’ve got to clean it off. Depending on the make and model of car, it could be a fairly involved process. More often than not, it involves the removal of the valve cover and intake manifold. From there, you can media blast the gunk off the back of the valves.

Many people use walnut shells, which are strong enough to scour off the build-up, but soft enough to not damage engine parts. To media blast, a technician will blow highly-compressed air mixed with, in this case, walnut shell pieces into the engine, which scrapes off the build up. At the same time, they’ll use a vacuum to suck up the excess dust and walnut shell pieces that go flying. 

Where Could I Get This Taken Care Of?

Most dealerships or independent mechanics worth their salt will have knowledge about carbon build up on GDI engines. Some brands are more proactive than others with recommending (or not) services to media blast or remove carbon build up on valves. 

What Happens if You Just Ignore It?

Well, you’ll have a lack of performance for one. The intake valves won’t be operating quite right, and your computer will try and compensate for it. Likely, the check engine light will turn on.

Eventually, serious damage could occur. A friend of mine’s dad had a 2013 Kia Soul with around 140,000 miles. The car had issues with a random misfire and suffered from generally low performance. A compression test revealed that cylinder one was low, so something was not getting a good seal.

Here’s what the engine looked like:

Finding and Fixing One of the Most-Ignored Downsides of Modern GDI Engines
Finding and Fixing One of the Most-Ignored Downsides of Modern GDI Engines

The car burned an exhaust valve. According to internet message boards, and conversations with technicians at the Kia dealership’s parts desk, this is fairly common for cars that have excessive carbon build-up that has never been cleaned. My friend’s theory is that poorly running engines (especially misfiring ones), tend to run lean, which raises the temperature of combustion dramatically. Eventually, that excess temperature burns engine parts, in this case, a valve.

Finding and Fixing One of the Most-Ignored Downsides of Modern GDI Engines
Finding and Fixing One of the Most-Ignored Downsides of Modern GDI Engines

This could have been avoided with a bit of preventative maintenance. The removal of the intake manifold and media blasting is somewhat more intense than say, dumping a bottle of “injector cleaner” in the car’s gas tank. You know, like that Lucas stuff the parts store cashiers are always pushing while they ring you up? Still, a bit of media blasting earlier could have saved this engine from a costly valve replacement job.

GDI engine might take a bit more work to maintain their port-injected-only counterparts, but I think it’s worth it. The real-world benefits to both power and economy can’t be underestimated, and there are some great engines on the market now that use this technology.

Kevin Williams

Kevin WilliamsKevin's been into cars his entire life, anything from the tiny kei cars in Japan, to the maybe not-so-good American barges of the 1980s. He's flipped more than 25 cars, only lost money twice, and has known how to make his dollar stretch as far as it can. If he ain't talking about cars, he's probably snacking on something sweet and cakey. Contact the author here.