By Brett Blackburn

High-quality fuels are essential to the reliable functionality of everyday vehicles, and to those ends, the TOP TIER™ Gas program has long been a successful means to ensure those high-quality fuels are widely available to drivers everywhere.

TOP TIER+™ is a voluntary standard that seeks to elevate the quality of gasoline fuel throughout North America, with the primary goal of providing greater deposit control to keep engines running cleaner and more efficiently. To participate, fuel marketers must ensure that every pump at every station dispenses fuel that adheres to the program’s quality standards—including the use of approved detergent additive packages, control of intake valve and combustion chamber deposits and more—making it widely available to drivers throughout the marketers’ service footprint.

In 2025, TOP TIER+™ formally introduced an update to the standard—the first of its kind since the launch of the program in 2005. Enter TOP TIER+™ , an elevated performance standard that aims to account for modern fuel injection technology commonly found in today’s passenger vehicles.

Because a majority of major North American fuel marketers participate in the program, the update to TOP TIER+™ will have a significant impact for many fuel marketers operating throughout the continent. With this in mind, this article will explore the coming updates to TOP TIER+™ , and what fuel marketers can do to prepare.

 

Drivers Behind TOP TIER+

The original TOP TIER program was launched when port fuel injection (PFI) engines were the most common engine technology throughout the car parc. It sought to elevate gasoline quality throughout the marketplace above the baseline standards established by the U.S. Clean Air Act in 1995, which phased out leaded gasoline, regulated fuel additives, and established standards for reformulated gasoline (RFG) and ultra-low sulfur gasoline (ULSG) to control smog-forming pollutants and tailpipe emissions from vehicles.

But much has changed in the 20 years since the program launched. Today, as original equipment manufacturers (OEMs) have sought to achieve fuel economy gains across all areas of the vehicle, gasoline direct injection (GDI) engines have effectively replaced PFI engines in modern vehicles for their ability to deliver improved fuel economy via more efficient combustion. That change has driven the development of TOP TIER+™, which will focus on evaluating gasoline’s ability to contribute to enhanced fuel injector cleanliness as well as other important criteria.

 

The Importance of Fuel Injector Cleanliness in GDI Engines

Why a focus on fuel injector cleanliness? It helps to understand the operational differences between GDI and PFI engine architectures.

GDI engines differ from PFI engines by placing the fuel injector directly in the combustion chamber, where it can be more precisely controlled by the vehicle’s engine control unit (ECU), and thus utilized to a highly efficient degree. There are major advantages to this setup, including improved fuel economy, increased power and torque, and reduced emissions. These performance advantages are why GDI has become the dominant engine technology today.

Comparatively, in traditional PFI architectures, the fuel injector is located outside the combustion chamber. Here, fuel is injected into the intake and then delivered over the intake valves into the combustion chamber. Fuel naturally flushes over the intake valves and prevents excessive carbon deposit buildup, creating a type of natural cleaning cycle for the valves.

In GDI engines, that cleaning cycle does not exist. Injectors are instead located in the hottest and most intense area of engine operation, where elevated pressure and temperatures can cause carbon to build up prematurely on the injector and piston tops at mileage as low as 20,000. PFI engines, by comparison, rarely see comparable buildup even at significantly high mileage. And because GDI efficiency depends on fuel injection precision, excessive buildup can be a significant disruptor, negatively impacting the engine’s efficiency, power, and emissions early in its operational life.

Drivers won’t likely notice fuel economy losses in real time. However, over the course of the vehicle’s service life, such buildup can have a significant impact on the vehicle’s fuel efficiency. Taken across the entire population of GDI engines, it’s a blow to the fuel economy gains the technology was specifically designed to achieve.

 

How TOP TIER+ Targets Premature Fuel Injector Deposits

TOP TIER+™ performance standards will be based on fuel performance in a series of new tests that are specific to GDI technology. They will evaluate the fuel’s ability to contribute to greater injector cleanliness, as well as particulate matter generation and pre-ignition performance.

One of the most significant performance requirements is that fuels will be required under TOP TIER+™ to actively clean up fuel injectors rather than simply prevent the generation of further buildup. The new specification requires 50% improved injector performance compared to a dirty reference test, measured through long-term fuel trim—a numeric indicator of how much the engine must compensate to achieve as-designed performance. TOP TIER+™ additionally measures injector pintle performance. The pintle is inside the injector and precisely controls the fuel flow out of the injector based on what the Engine Control Unit tells it. The shorter the time it takes to open to inject fuel, the optimal the vehicle’s performance. The longer it takes, the less efficient the combustion cycle, requiring overcompensation with more fuel and therefore more carbon build up on injector.

By helping to eliminate deposits from already dirty injectors, this should make for a significant benefit for the entire vehicle population. TOP TIER+™ formulations should be able to help restore some fuel economy and emissions performance to even older-model vehicles, as GDI engines have existed in significant numbers since roughly 2010.

 

How Fuel Marketers Can Prepare for TOP TIER+

To achieve new levels of performance and to meet TOP TIER+™ certification, fuel marketers will need to source new additive chemistries that can contribute to fuel injector cleanliness.

How do such chemistries work? At a basic level, high-performance deposit control additives attach to carbon deposit molecules on the fuel injector. The additive then pulls those molecules into the fuel stream, where they combust along with the fuel within the combustion chamber. Finally, any associated emissions are mitigated by the vehicle’s catalytic converter.

Over time, the effects can be dramatic. A GDI engine that is serviced with high-quality fuel will continuously regain efficiency that had been hindered by excessive injector buildup, restoring the engine’s operation closer to its original design intent.

The deadline for TOP TIER+™ compliance is set for February 2027. Fuel marketers intending to upgrade their formulations by that time should begin working with their additive technology partners now to ensure proper formulations. Depending on your market needs, your partners may also be able to help further differentiate your fuel formulations.

The bottom line is that TOP TIER+™ should deliver real benefits for modern engine technology. GDI engines’ ability to meet their full potential depends on it.

 

Brett Blackburn is a Regional Product Manager of Consumer and Professional Fuel Additives for Lubrizol.