Direct Fuel Injection: The Good, The Bad, And The Walnut Shells

Posted on: 29 May 2015

Have you recently purchased a BMW with direct fuel injection? Are you wondering what the benefits of such a system are, and if there are any disadvantages to it? If so, read on for everything you need to know about this latest fuel-feeding technology.

The Faster Fuel Feed Of Direct Fuel Injection

A conventional fuel injection engine sprays gasoline into your vehicle's combustion chamber at a rate of approximately 50 - 100 psi. Conventional fuel injection systems are a step up from fuel systems that rely on carburetors to control the flow of gasoline to the engine.

Some luxury car manufacturers have taken things a step farther, though. They've created systems that spray gasoline into vehicle combustion chambers at several times the velocity of traditional fuel injection systems. This high-powered fuel spray system is called direct injection and it has several benefits and a few disadvantages.

Better MPG And More Power

Direct fuel injection systems offer more complete fuel combustion, thus enabling the driver to get more miles per gallon of fuel and more vehicle power. How much less gas will you use and how much more power will you have? You can expect to use about 20 percent less fuel and have 10 percent more power than if you drove a vehicle that was powered by a traditional fuel-injected engine.

You can also expect to leave less of a thermal footprint on the world, considering direct fuel injection systems emit fewer carbon emissions than both carburetor-fed and traditional fuel injection systems. 

Of course, this is all contingent on your engine functioning properly.

When Direct Fuel Injection Goes Bad

Because of the high-powered rate that fuel is sprayed into the combustion chamber of your car, the airflow within the chamber can be disrupted. When this happens, your fuel will burn unevenly. When your fuel burns unevenly, bits of carbon are left behind as a combustion byproduct.

In direct fuel injection motors, the intake valve actually enters into the combustion chamber to deliver air and fuel. When it does, any combustion byproducts that happen to be in the chamber stick to your intake valve and build up on it. This carbon buildup is bad news. It prohibits the amount of fuel that can actually get to your engine, making your vehicle sluggish and in some instances, stopping your vehicle dead in its tracks.

In traditional fuel injection systems, the slower release of the gasoline from the intake valve allows the gasoline to linger long enough on the valve to clean these carbon deposits. In direct fuel injection systems, the fuel rushes forth with such force, that it never even touches these carbon deposits.

Cleaning The Carbon Buildup

If your vehicle develops carbon buildup on its intake valve, you have a few options for taking care of it. You can take your vehicle to a mechanic and ask them to replace your valve, or you can pull the valve out of your vehicle and get to work on scrubbing it with a carbon dissolving solution (available at most local hardware stores).

A third option, devised by BMW, is to have a mechanic blast the carbon buildup off of your intake valves with walnut shells. While it's a peculiar solution, finely crushed walnut shells have proven effective for cleaning carbon buildup without being so abrasive as to damage your intake valve.

Direct fuel injection systems offer drivers more power and fuel efficiency than ever before, yet, there are a few drawbacks to the design. If your new BMW becomes sluggish or bogged down, visit a BMW auto repair shop and ask them to inspect your intake valve for carbon buildup.