Direct Injection Could Be Maintenance Nightmare

June 29th, 2011
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?

-tgriffith

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  1. Doug
    December 10th, 2013 at 22:43 | #1

    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.

  2. Randy
    June 30th, 2011 at 07:30 | #2

    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.

  3. June 29th, 2011 at 16:02 | #3

    Direct injection has been about for some time now I dont see why Holden built GM 6s should have extra trouble in z Caddy or Buick

  4. Jim Redd
    June 29th, 2011 at 12:19 | #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.

  1. November 6th, 2013 at 16:02 | #1
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