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Thursday, March 17, 2016 - 06:00
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Tech tips come from a variety of sources, and some are certainly better than others. And as the technical editor for the magazine, I get them fairly often.

Recently, my friends at Bosch sent me one regarding the increasing problem of carbon build-up in GDI (Gasoline Direct Injection) engines that I knew I had to share. So, with all due credit to Stephen Albert, Product Manager – Port Fuel and Gasoline Direct Injection Systems for Robert Bosch, LLC, here it is!

GDI engines typically build carbon on the back of the intake valve (!) and along the intake runner (2). (Photo Courtesy: Bosch)

Addressing Carbon Buildup in GDI-Equipped Vehicles
Driven by strict emission laws and a growing demand for low fuel consumption, an increasing number of vehicles equipped with gasoline direct injection systems (GDI) are now being seen on roads today.  However, a common complaint about these vehicles has been the buildup of carbon deposits inside the cylinder head.

What causes carbon deposits in GDI-equipped vehicles?
The cause of carbon buildup can vary by vehicle make, as engine management systems can mitigate the carbon buildup in certain vehicles by something as simple as an ECU update. Essentially, carbon buildup occurs due to a combination of low quality fuel, short, frequent cold weather trips or positive crank case ventilation, which may leave an oily layer around the intake valve. These factors, in conjunction with the operating temperatures of the engine casing, lead to a buildup of carbon deposits.

Timing may also have an effect if the intake valve stays open long enough to be exposed to unburned fuel. Finally, the location of the GDI injectors in the cylinder head plays a significant role in carbon buildup because it does not allow for the fuel sprays to reach the back of the intake valve, making it difficult to keep the intake runners and valve clean. 

What is the impact of carbon buildup on drivability, performance, emissions and fuel economy?
With regard to drivability, one of the more common symptoms is a lack of power, especially when driving at higher speeds. Other symptoms could include cold stalling and cold-start difficulties, including rough running when the engine is cold. There is also the possibility of a failed NOX emissions test and/or excessive ping on acceleration.

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In some cases, carbon buildup may cause one or more cylinder misfire codes (P030X), which will result in fuel inefficiency and poor performance. This occurs when an insufficient number of cylinders fire while the vehicle is in operation.

If the presence of carbon deposits is not detected early enough or the buildup is severe, the check engine light may turn on and the vehicle is likely to fail inspection.

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