Unintended Consequences Drive GDI Engines to Your Shops - Part 3
Foundation recap; Part 1 (see May issue for details, sources, etc.) addressed how:
Due to emissions and CAFE fuel economy mandates, manufacturing turned to gasoline direct injection (GDI) engine technology that now arrives in shops suffering from unintended consequences as they age.
· GDI engines differ from previous engines — including port fuel injection (PFI) — in ways that change their “…repair process and maintenance program.”
· GDI engines arrive “…with mysterious complaints. … Problems can affect engine performance in as little as 3,000 miles. Neglected treatment may require a costly upper-end teardown...” Note: costly.
· GDI engine owners can research and assume to know more about their GDI problems than uninformed service providers. Word-of-mouth on uninformed service providers will drive customers away, but customers return to the informed.
· Information in this series originates from sources that manufacture, test or report on GDI engines. Dig for yourself, including the thousands of SAE Papers and articles on GDI problems listed by category in Part 1.
· This series provides a valuable training tool because, “In 90 percent of the motor industry, keeping up-to-date with changes in technology is beyond most workshop owners’ budget. … Technicians could spend at least 10 working days of a month being trained…”
Part 2 added to the foundation (see July issue for details with sources):
· Carbon deposit engine design issues
· GDI increased engine deposits
· Deposits interfere with GDI’s exacting requirements
· How we drive and
· Typical driving impacts GDI engine deposits.
Now let’s address another foundation issue before moving into specific GDI engine component service opportunities.
Ethanol Gasoline Mandate Problems
Part 1 introduced a root cause of GDI engine problems: While direct injection (DI) functioned well in diesel engines since Rudolf Diesel’s 1892 patent, experts worry that due to differences in diesel fuel (called “gas/oil” in Europe) vs. gasoline components and combustion and their byproducts, GDI may never prove the best choice.
Auto Guide’s article “Should You Buy a Car with Direct Injection?” (figure 1) addresses a significant ethanol/GDI issue — injectors.
“Another problem with direct injection is with ethanol fuel. Ethanol is known to speed up the corrosion rate of some metals that are used in an engine. With the higher pressure of a direct injection engine, and thanks to the fuel injector being exposed to in-cylinder explosions, there’s a higher chance of a problem or failure.”
Service providers should know with GDI injector pressures at 2,200 PSI and higher (vs. PFI injectors at 40–60 PSI), “…professionals must also be aware many [GDI injector] manufacturers might require a complete fuel rail replacement when a single fuel injector is replaced for safety reasons.”
To avoid redundancy, we’ll assume familiarity with ethanol concerns. You’re likely aware engine problems caused by the ethanol mandate motivated automotive groups, including numerous manufacturers, to take legal action against the EPA — as covered by sources such as Fox Business.
Knowledge of ethanol issues turns critical when diagnosing today’s engines.
Throttle Body Deposit Problems
Don’t take our word for it; you can research more than 200 SAE papers and journal articles containing all the words, “Gasoline Direct Injection Throttle Body Deposits.”
Just remember, as the weary gold prospector grumbled, “It takes lots of digging to find the nuggets.”
Nugget example: SAE Paper 2001-01-1202 reports that in GDI engines, “Throttle body deposits will build over time to a point where either the blade cannot move freely or airflow is significantly reduced at the so-called limp home mode position of the blade. … Either condition results in a potentially dangerous or non-functional engine running condition.”
This SAE Paper continues, “Naturally this is something that needs to be prevented and cannot be compensated for by the engine management system or cleaned up by [fuel] additives since there are none to be introduced in that area.”
Emission Controls Increase Deposits
Those of us who “go way back” recall engines with road draft tubes, better known as dump tubes or blow-by tubes. So named for good reason; while located high enough on the block to minimize oil loss, these tubes dumped blow-by combustion and crankcase vapors with oily droplets, including lots of hydrocarbon, directly into the atmosphere and onto the road.
Soon after 1958 when GM learned these road draft tubes expelled about half of the polluting hydrocarbons coming from gasoline engines, positive crankcase ventilation (PCV) — already developed during WII for deep-water fording tanks — replaced road draft tubes and became the standard emissions control system. (See figure 2 for a recent diagram.)
SAE Paper 200-01-2856 documents an unintended consequence: crankcase contaminants, routed by the PCV system into intake air, contribute to intake valve deposits.
How? The PCV system routes oily crankcase vapors and droplets — with a baffle, screen or mesh to reduce droplets — into the intake manifold where they can cause sticky coatings on intake valves. When augmented by exhaust gas recirculation (EGR) system’s exhaust carbon particles and heat, these intake valve coatings bake into larger, harder, crusty carbon deposits. SAE Paper 2002-01-2660 confirms, “A concern is [GDI engine technology’s] propensity to form deposits on the inlet valve. …these deposits can lead to poor drivability and deteriorating emission performance.”
Future articles address how preventive maintenance offers a valuable intake valve deposit service opportunity and present other GDI engine service opportunities. Plus, we’ll end with future service trend indicators.