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Dual Port and Direct-Injection Technology: What You Need to Know About the Next Generation of Engine Design

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Editor’s Note: When working on the March 2018 TechSpec article about the 2018 Ford F-150, I came across the following statement in reference to new engines available in the truck: “significant upgrades including advanced dual port and direct-injection technology, plus spray-on bore liner technology.” Never before in my TechSpec writings had I come across an engine utilizing both advanced dual port and direct-injection technology, so I reached out to one of the smartest guys I know to shed some light on the subject.

  Gasoline Direct Injection (GDI) represents the fastest-growing engine market, but there are many unintended consequences associated with these engines as they age — not only in Ford EcoBoost engines, but many others, as well. In this article, I (a Ford fan) will summarize Ford’s EcoBoost redesign issues.

Following a 2013 class-action lawsuit, Ford announced their 2017 “all-new 3.5-liter EcoBoost engine.” Automotive News added that Ford’s clean-sheet redesign of the engine included a new block, cylinder head and turbos, in addition to a new intake system.

You could say, Ford’s original EcoBoost engine falls under the category of rushed-to-market engines. Why rushed-to-market? In response to mandates, with dates and fines, for improved economy and emissions, manufacturers sometimes rush new technologies. The US Congress passed Corporate Average Fuel Economy (CAFE) mandates for cars and light trucks, with requirements increased by increments to “54.5 mpg by 2025” (figures in flux). If OEMs don’t meet these requirements, there are fines. For instance, Mercedes-Benz paid CAFE fines of $30.3 million for 2006 and $28.9 million for 2007.

When an engine is rushed-to-market, sometimes there are design characteristics that can be overlooked. Deposits are often a prime cause for redesigns. According to SAE Paper 2002-01-2659, “Engine deposits are … the most critical of [engine design] characteristics.” SAE Paper 1999-01-3690 reported that early GDI engines, “suffered from severe deposit problems, which could not be overcome at the time.”

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Fig. 1: Port Fuel Injection (PFI)

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Fig 2: Gasoline Direct Injection (GDI)

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While GDI was great in theory, there was one really big problem: While port fuel injection helps wash intake valve inlets (Fig. 1), GDI sprays gasoline directly into the combustion chamber with no intake valve inlet washing (Fig. 2). SAE Paper 1999-01-1498 added that, “IVD (intake valve deposits) are unexpectedly higher in the GDI engines than the PFI … with no (or very little) fuel expected to contact the valves in GDI engines.”

GDI sprays gasoline directly into the combustion chamber under much higher pressure (2,200 psi or more) than PFI’s intake manifold spray (40-60 psi). Increased GDI contaminants blow past low-tension piston rings into the oil sump. Then, positive crankcase ventilation (PCV) passes oil-laden contaminants into the intake air stream where, according to SAE Paper 2002-01-2660, oily PCV crankcase vapors and droplets combine with exhaust gas recirculation carbon particles and heat to layer over sticky intake valve coatings and bake into deposits. This creates larger, harder and more crusty deposits in the fuel system.

Dual Fuel Delivery Systems: PFI Combined With GDI

Ford, and other OEMs, have combined PFI with GDI for “advanced dual port and direct-injection,” also known as dual fuel delivery. Examples include:
  • Redesigned Ford 3.5L EcoBoost and V6 engines
  • Lexus 2GR-FSE engines
  • Audi’s VW Group 3.0-liter V-6 and 5.2-liter V-10 engines
  • Toyota’s 2.0-liter in-line four-cylinder engines built by Subaru, and D4-S 3.5-liter V6 and 5.0-liter V-8 engines.

Dual fuel delivery systems with GDI and PFI attempt to combine the advantages of both systems, especially with PFI’s intake valve washing added to GDI’s increased fuel economy and precision. But dual fuel delivery significantly increases complexity and costs (see Fig. 3, Toyota’s D-4S [note yellow circles], and Fig. 4, VW Group’s Audi).

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Fig. 3: GDI and PFI close-up on Toyota's D-4S engine (note yellow circles)

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Fig. 4: VW Group's Audi

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A forum writer asserted that OEMs resorting to combined GDI and PFI have, “finally thrown in the towel concerning carbon deposits on the intake valves and added back port fuel injection that cleans the valves with gasoline along with the GDI system.”

So, Tammy Neal posed an interesting question when we were discussing this article topic. “Just because Ford’s engine was redesigned with this new technology, does that mean it actually fixes the GDI problems?” she asked.

It’s a wait-and-see proposition with GDI’s history of unexpected problems due to unintended consequences.

Remember, just because Ford redesigned their engine, the previous-generation engine problems don’t sputter off and disappear forever into salvage yards. Previous problem engines live on to arrive in shops, sputter and all, with customers hoping for a fix. That’s why it’s important to stay viable on aging engine issues, including millions of EcoBoosts.

Fig. 5: EcoBoost intake valve deposit at 20,000 miles

Larger, harder and more crusty GDI deposits often require preventive maintenance to prevent sputter, misfire, hesitation and loss of volumetric efficiency and power. It’s very important to keep reminding motorists that preventive maintenance can help avoid costly repairs down the road. Even drivers of low-mileage vehicles are at risk. Need proof? Check out Fig. 5, which is a tech’s borescope showing an EcoBoost intake valve deposit at only 20,000 miles.

Do dual fuel delivery systems eliminate the need for preventive maintenance? Certainly not — especially with deposit problems affecting both PFI and GDI engines.

The best way to fight engine deposits is to “deposit” preventive maintenance, to keep an engine functioning well and help customers avoid expensive repairs.

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