Direct Injection Could Be Maintenance Nightmare

2011 Cadillac STS

Cars with direct injection: Trouble waiting to happen?

Writers across the automotive blogosphere are guilty of using the words “direct injected” as an adjective meant to give some punch to the description of a new engine. I am no exception:

Buick will offer a no-extra-cost 3.6-liter direct-injected V6…

But what does “direct injected” really mean? Many readers of this blog are enthusiasts and know exactly what the term describes, but for others, it’s just more techie jargon that sounds cool in front of the term “V6.”

I’ll briefly describe what it means, but more importantly, ask if direct injection is the savior some automakers believe. Some evidence is beginning to crop up that could translate to future maintenance disasters.

First, for the uninitiated:

A direct-injected engine injects pressurized fuel directly into the combustion chamber, rather than into an intake manifold where it gets mixed with air and then enters the combustion chamber.

The results of direct injection are improved fuel economy and cleaner emissions due to a leaner fuel burn, which Ford, GM, Volkswagen, Hyundai and others love to tout in advertisements and press releases.

The problem, though, is pretty dirty.

Engine apartAuto Observer reports that the issue lies in the tendency of direct-injected engines to build up a layer of carbon around the intake valves that can significantly affect the performance and economy of the engines over time. The dirty grime builds up in a DI engine because, unlike a port-injected engine, there is no constant spray of fuel to keep the deposits washed off the valves.

The repair can be quite expensive, though some guys at a BMW forum swear that “giving the car a good flogging” once in a while burns the deposits off. Maybe… but that’s probably not a substitute for dropping the bucks and having the valves cleaned.

Volkswagen has known about the DI problem for quite some time, saying in a patent application that the carbon deposits can have extremely negative effects on performance.

Owners of Cadillac’s direct-injected V6 have also reportedly started to complain, though GM remains adamant that it has engineered around the problem.

Whether the problem exists only in the Caddy owners’ heads or not, it’s becoming quite clear that direct injection still has some hurdles to clear before automakers roll out the technology across the board.

Would you buy a vehicle with a direct-injected engine knowing about the potential carbon layering problem?


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  1. I have 2012 hyundai veloster and its a gdi. Ive had issues and hyundai really doesnt have a answer. They did an induction service and it didnt really help. I had to do that a few times to get the valves clean. I run pennzoil platinum 5w30 and a fram ultra filter. I change my oil on or before 3,750 miles which is what hyundai says to do. I also run tectron complete fuel system in my car atleast twice between oil changes. Ive changed the pcv valve twice and so far so good. I usually go 10,000 miles then do a crc intake valve fogging through the induction and so far its worked to keep everything smooth. Hyundai doesnt really know what else too do. Its a known issue. Alot of beemer folk say not to baby the car so once in awhile ill get her out on the highway and run her in 4th gear and keep the tach uo around 4000 rpms for ten minutes. Some say it cleans the valves. Who knows hopefully the car will last me a few years.

  2. I will definately be avoiding GDI and turbos for as long as I have the option. In fact, I distrust GDI so much Id buy a hybrid first.
    Its not just the intake gunk that bothers me… 3000 psi of fuel pressure??? Thats nuts. This technology is a equivalent to a tsunami thats still miles out at sea. And when the public begins to scream a lot of car makers are going to paying big bucks to settle class action suits.

  3. It’s interesting that the much more thorough combustion of direct-injected engines should result in carbon crud deposits on the valves. After all, more thorough combustion should imply higher combustion temperatures and less emissions. I suspect that car makers will design valves to operate at higher temperatures, which should help prevent carbon deposits from forming. These types of engineering challenges are common and every new technolgy produces some unwanted effects that must be addressed. Remember when unleaded fuel was introduced in the early 1970’s? (well, some of you young pups weren’t born yet.) Valve seats tended to erode because they lost the lubrication provided by tetra-ethyl lead compounds in the fuel, which had to be addressed by using hardened valve seats. The whole lead-valve seat thing was a byproduct of higher compression engines. My 1953 Ford tractor runs fine on unleaded fuel because the low-compression engine never needed leaded fuel in the first place.

  4. I’ll just stick with the car I have… a regular, normally aspirated, port injected 4-cylinder. Nothing fancy but it works without breaking the maintenance budget.

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