Toyota D-4S: Port Fuel Or Direct Fuel Injection? Why Not Both?

d-4s

You may soon see a Toyota vehicle that combines both direct fuel injection and port fuel injection. This innovative system, known as the D-4S or Dynamic Force Engine, incorporates port fuel injectors in the intake manifold as well as a direct injection fuel pump. Toyota refers to this system as “superior” (the “S” in D-4S) and initially introduced it in the Lexus GS SUV with a V8 engine. However, the D-4S system is different from the “cold start” or “dousing” injector systems found in V6 engines from the early to late 2000s.

The direct fuel injectors in the D-4S system function similarly to other direct fuel injection systems, while the port fuel injectors are not there to clean the intake valves but rather to provide fuel to the engine. Both sets of injectors work together to achieve the best fuel mixture in the cylinder. However, it’s important to note that port fuel injection and direct fuel injection systems each possess individual advantages and disadvantages.

Port fuel injection, under specific conditions, can offer better vaporization. However, port fuel droplets may drop out of suspension upon contact with the intake valve before entering the combustion chamber. On the other hand, direct fuel injection excels at cooling the combustion chamber and controlling fuel trims in certain conditions. Nevertheless, direct injection can produce soot due to a lack of vaporization at specific engine speed and load conditions. Additionally, port fuel injection can deliver more torque in certain circumstances.

Toyota utilizes a blended approach, combining both port and direct fuel injection to optimize performance, emissions, and fuel efficiency. Determining whether the port injectors, direct injectors, or both are active depends on several variables, including throttle position, load, engine speed, and temperature.

D-4S Engines & Models

More and more engines are now equipped with the D-4S injection system. It was first introduced in Lexus GS models in 2007, followed by the Toyota/Scion FR-S F86 in 2012. In 2015, the Highlander and Tacoma also received the D-4S system as an option. Most recently, the four-cylinder engine used in the 2017 Camry received the D-4S system. To identify an engine with this system, look for port fuel injectors and a high-pressure fuel pump.

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How It Works

According to Toyota, during low-to-medium engine loads, the D-4S system utilizes both direct-type and port-type fuel injection together, or one of them, to create a homogeneous mixed air and fuel mixture, contributing to stable combustion processes. During high engine load ranges, only the direct-type fuel injection is used to cool down the intake air with the chilling effect of fuel vapors, improving charge efficiency and anti-knock properties. Under specific conditions, the intake valves open to allow the homogeneous air/fuel mixture into the combustion chamber, and fuel is injected during the first half of the intake stroke.

During a cold start, the system times the opening of the port and direct fuel injectors to decrease emissions and achieve stratified combustion. Fuel is injected into the intake port from the fuel injector assembly (for port injection) immediately after a cold engine start and during the exhaust stroke. Fuel is also injected from the direct fuel injector near the end of the compression stroke. This results in an air-fuel mixture that is stratified, with the area near the spark plug being richer than the rest of the mixture. This process allows for a retarded ignition timing, which raises the exhaust gas temperature and promotes rapid warmup of the catalysts, improving exhaust emission performance.

The changeover from port to direct injection is impossible to detect without a scan tool. The Electronic Control Module (ECM) controls the fuel pump, calculating low-pressure fuel demand based on the vehicle’s state and signals from various sensors. Fuel pump control is achieved using a three-phase Pulse Width Modulation (PWM) control system.

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Similar to other late-model Toyota vehicles, the fuel pump stops when any of the Supplemental Restraint System (SRS) airbags are deployed. This feature minimizes fuel leakage.

Both sets of injectors use the same fuel pump to provide fuel pressure to the fuel rail for the port fuel injectors and the high-pressure fuel pump on the engine. The pump should produce 51 to 73 psi while running and for up to five minutes after the engine has been turned off. If the pump fails, neither system will function.

The high-pressure fuel pump can generate 435 to 725 psi. Earlier D-4S Lexus V8 models with this system featured a return line to the tank on the high-pressure side of the fuel system. However, newer models use a spill valve and improved pump solenoid control, resulting in a more efficient and returnless system. The spill control valve, located in the inlet passage of the fuel pump assembly, regulates the pressure by allowing uncompressed fuel to spill back into the low-pressure side of the system when the direct fuel injection system is not in use. When the spill valve is open, the pump operates quietly since it’s not compressing fuel. Moreover, under certain idle conditions, the usual ticking sound of the pump is eliminated.

The direct-injection fuel injectors in the D-4S system are equipped with a special clamp that continuously pushes on the high-pressure fuel injector rail using the force of a spring. This prevents the fuel injector assembly from moving when fuel pressure is applied during engine start-up with low fuel pressure. The clamp reduces vibration and noise while ensuring a reliable seal. When servicing the high-pressure side of the fuel injection system, it’s essential to replace these clamps along with the recommended fittings.

Other manufacturers, including Audi and Ford, are also adopting the Toyota D-4S dual-injection system, which offers the best of both worlds while avoiding carbon buildup on the intake valves. As component costs decrease, we can expect to see these types of systems incorporated into more engines.

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Article courtesy ImportCar.

FAQs

Q: What is the D-4S system?
A: The D-4S system is Toyota’s Dynamic Force Engine that combines both direct fuel injection and port fuel injection to optimize performance and emissions.

Q: Which Toyota vehicles have the D-4S system?
A: Various Toyota and Lexus models have been equipped with the D-4S system, including the Lexus GS, Toyota/Scion FR-S F86, Highlander, Tacoma, and Camry.

Q: What are the advantages of the D-4S system?
A: The D-4S system offers better vaporization, cooling of the combustion chamber, control of fuel trims, and improved torque under different conditions.

Q: How does the D-4S system work during a cold start?
A: During a cold start, the D-4S system utilizes both port and direct fuel injection to decrease emissions and achieve stratified combustion, promoting rapid warmup of the catalysts.

Conclusion

The Toyota D-4S system combines the advantages of port fuel injection and direct fuel injection to optimize performance, emissions, and fuel efficiency. By utilizing both types of fuel injection under different engine conditions, Toyota ensures the best possible fuel mixture in the cylinder. The D-4S system can be found in various Toyota and Lexus models, with more manufacturers adopting this innovative technology. As the industry continues to evolve, we can expect to see more engines benefit from the dual-injection capabilities of the D-4S system.

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