Unintended Consequences Drive GDI Engines to Your Shops - Part 4 - Intake Valve Deposits
A well-documented gasoline direct injection (GDI) problem is intake valve deposits, caused by the absence of intake valve washing.
Why is this important for NOLN readers? Owners learn of GDI issues — including reports of a leading manufacturer replacing cylinder heads due to excessive intake valve deposits at only 20,000 miles, the same OEM introducing a completely redesigned GDI engine for 2017 and expect their service providers to know what’s going on.
This series provides valuable training because, as reported by ASNU, “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 per month being trained.”
So this article provides condensed information to “improve your presentations instantly,” as Kit Sullivan suggested in his August article.
Note: Series information originates from sources that manufacture, test or report on GDI engines. We also recommend personal research, with thousands of Society of Automotive Engineers (SAE) technical papers and articles on GDI deposit issues listed by category in our May article.
Why review previous NOLN articles for GDI problem details with sources?
• GDI represents the fastest-growing vehicle engine technology, often rushed to market due to government mandates for fuel economy and emissions.
• Consumer Reports’ article titled “Direct-injection [GDI] engines improve performance and save fuel, but at a price;” subtitled, “Cars with this technology might end up in the repair shop more frequently”
• Consumer Reports adds, “But those engines are also having reliability problems, something automakers are trying to keep quiet.”
An unintended consequence of reducing emissions via positive crankcase ventilation (PCV) is increased intake valve deposits. This is more challenging and costly for GDI engines because, according to Leman Public Relations, they can arrive for repairs “…with mysterious complaints. Problems can affect GDI engine performance in as little as 3,000 miles. Neglected treatment may require a costly upper-end teardown.”
The root problem is, when compared to port fuel injection (PFI), GDI engine design provides no intake valve washing. (See fig. 1 and 2) This problem’s severity is shown by more than 1,000 SAE technical papers and articles containing all the words — gasoline direct injection valve deposits.
An example: “A concern is [GDI’s] propensity to form deposits on the inlet valve…these deposits can lead to poor drivability and deteriorating emission performance.”
To reduce engine emissions from blow-by, OEM’s replaced the crankcase dump tube with PCV, which increases intake valve deposits. That’s a greater problem with GDI, as more blow-by contaminants enter the crankcase due to increased unburned fuel, increased compression and reduced-tension piston rings.
How does PCV increase intake valve deposits?
The PCV system routes oily crankcase vapors into the intake manifold where they can cause sticky coatings on intake valves. When augmented by the exhaust gas recirculation (EGR) system’s exhaust particles and heat, these intake valve coatings accumulate and bake into larger, harder, crusty deposits. (See fig. 3.)
AA1 Car’s article, “Intake Valve Deposits in Gasoline Direct Injection Engines” adds, “The thicker the carbon deposit buildup on the valves, the worse the driveability problems.”
Adding to the problems, intake valve deposits impact critical air swirl and tumble in GDI engines. Intake valve deposits restrict airflow and interfere with stratified and homogeneous combustion, a technology that can involve variable manifold tumble flaps where carbon and vacuum leaks wreak havoc.
SAE technical papers report that intake valve “deposits greatly affect driveability and exhaust emissions” by “absorbing fuel during acceleration and releasing fuel during deceleration” and “insulating the heat release from the cylinder, and this phenomenon is the cause of bad fuel vaporization.”
This is also a worst-case scenario: Intake valve deposits can eventually prevent proper valve closing and cause burned valves with compression loss and huge repair costs.
To illustrate the severity of this issue, the following OEMs resort to expensive and complex dual-injection technology by combining both GDI and PFI:
• Toyota D-4S
• Lexus 2GR-FSE
• Audi EA888 (see fig. 4)
• 2017 Ford Ecoboost 3.5L V6 - Gen 2
The Solution – Preventive Maintenance
Bosch reports that GDI changes the maintenance program. Informed customers understand that preventive maintenance intake valve cleaning provides their best return on investment, when the alternatives are walnut shell blasting with clean-up or a mechanical teardown for an engine head rebuild and/or replacement.
Return Customer Concern
Being informed matters, as customers research and assume to know more about GDI problems than uninformed service providers. Word-of-mouth on uninformed service providers drives customers away, while customers return to the informed.
We’ll move downstream into the combustion chamber, addressing GDI fuel injector and combustion chamber deposits, and top it off with a read on trend indicators.