Technical
Gasoline direct injection systems Diagnosing and servicing GDI
By Bill Fulton
F
or those of you who can recall when the manufacturers first came out with the port fuel injected systems, you will remember it wasn’t long before we saw some predictable problems surface on these vehicles, such as olefin and diolefin buildup on the pintle area of the injector causing a restriction. We have all done the chemical cleaning process through the injector rail to improve or eliminate the common lean conditions. In addition, carbon buildup on the back of the intake valves was also a common problem. If you can recall, the European manufacturers used a walnut shell blasting unit to clean these valves. With the introduction of deposit resistance injectors (DRI), the pintle restriction has been greatly improved, but not completely eliminated. Due to the efforts by the American Petroleum Institute (API), the Society of Automotive Engineers (SAE) and the Environmental Protection Agency (EPA), modern-day toptiered gasoline detergent additives have been increased to nearly eliminate this problem. Have you noticed over the last few years that
Photo: Thinkstock
Gasoline direct injection (GDI) introduces the fuel charge directly into the combustion chamber instead of via an intake runner. GDI systems differ in terms of operation and operating voltages. Servicing these systems involves diagnostic and repair challenges and precautions unique to GDI. In this article, Bill Fulton offers insight to aid in understanding these issues. when the OE manufacturers come out with a new system, there always seems to be new problems that surface over time and mileage? That’s truly the case here when addressing the modern-day gasoline direct injected (GDI) systems. But before we address these predictable problems, let’s look at the dynamics of these systems.
The fuel tank Let’s begin at the fuel tank. There is a low side supply side and a high pressure side of the GDI systems. There are two systems known as mechanical returnless systems and electronic returnless systems. On the mechanical returnless systems the supply side fuel pressure regulator is in the tank and part of the fuel pump module. To my knowledge, GM is the only manufacturer that still supplies a conventional fuel pressure test port to check for low side supply pressure with the conventional fuel pressure test port. Go figure. Ford supplies some through model year 2010, only to eliminate it in model year 2011. A T-fitting adapter can be purchased from the OTC people to manually use your conventional fuel pressure test gauge. Normally, the low side supply pressure will usually range between 50
14 | ASP April 2018
