Ideal Fuel Pressure For A Supercharged 1Uz Engine

The stock fuel pressure for the 1UZ-FE motor is 290kpa (2.9bar, 42psi). This can be measured with the vacuum line to the FPR disconnected and plugged to prevent leaks and an inaccurate reading. The base fuel pressure should be anywhere from 35 to 38 psi, and the fuel pump should be able to maintain this pressure under load. A drop in fuel pressure under boost may indicate that the fuel pump is not keeping up with the engine's demands. Upgrading to a high-capacity fuel pump can help address this issue, but it is important to note that this may also require upgrading the fuel line size and converting to a return-style fuel system to stabilize fuel pressure and prevent vapor lock.

Fuel pressure drop under boost

A drop in fuel pressure under boost can be caused by various factors, and it is important to identify the root cause to ensure optimal engine performance and avoid potential issues. Here are some possible reasons for the fuel pressure drop and steps to address them:

Fuel Pump Voltage

It is important to ensure that the fuel pump is receiving adequate voltage. Check the voltage at the battery and the fuel pump under different load conditions. If there is a significant voltage drop, consider rewiring the fuel pump with a larger gauge wire to provide sufficient voltage and rule out electrical issues as the cause of the fuel pressure drop.

Fuel Line and Regulator

The size of the fuel line and the location of the fuel pressure regulator can impact fuel pressure. Upgrading to a larger fuel line, such as -8AN for higher horsepower applications, can help stabilize fuel pressure. Additionally, relocating the fuel pressure regulator closer to the rail can improve fuel pressure stability by reducing the distance the fuel has to travel. This may require fabricating a return-style fuel system, which involves sending the fuel past the regulator back to the pump or tank.

Fuel Pump and Injectors

A faulty or inadequate fuel pump can struggle to keep up with the engine's fuel demands under boost. Ensure that the fuel pump is in good condition and capable of delivering the required fuel volume and pressure. Additionally, leaky or faulty injectors can contribute to fuel pressure issues. Inspect the injectors for any signs of leaks or damage and replace them if necessary.

Fuel Pressure Regulator

A faulty or incorrectly adjusted fuel pressure regulator can also lead to fuel pressure drops. Check the fuel pressure regulator for any signs of damage or leaks, especially if the fuel pressure fluctuates rapidly or drops significantly under high boost. You may need to adjust or replace the fuel pressure regulator to maintain the correct fuel pressure.

Fuel Blend and Engine Condition

The type of fuel and its blend can impact fuel pressure. Different regions may have variations in fuel blends, which can affect fuel pressure and injector performance. Additionally, engine condition and tightness can play a role. A tighter engine may require slightly larger injectors or fuel pressure adjustments to compensate for the fuel pressure drop.

Fuel System Components

Ensure that all fuel system components are properly installed and secured. Check for any kinks, leaks, or restrictions in the fuel lines, as well as the correct installation of O-rings and other sealing components. A restriction or leak in the fuel system can lead to fuel pressure drops under boost.

Fuel Pressure Sensor and Tuning

It is important to monitor fuel pressure using a fuel pressure sensor and log the data for analysis. Compare the logged fuel pressure values with the expected fuel pressure for your specific setup. If the fuel pressure drop is confirmed, adjustments to the injector scaling or fuel pressure compensation in the tune may be necessary. This can involve creating correction factors or adjustments based on the deviation from the static fuel pressure.

Fuel pump voltage

When choosing a fuel pump, it's essential to consider the voltage requirements and ensure your vehicle's electrical system can provide the necessary power. Most fuel pumps operate at 12 volts, but high-performance fuel pumps may require higher voltages, such as 13.2 volts, to function optimally.

In a forum discussion, a user with a Lexus mentions that they are considering a Bosch 044 fuel pump for their 1UZ engine. They seek advice on whether this pump will be adequate for their needs, including possible future modifications involving tuning and forced induction. Another user responds, recommending the Bosch 044 as a high-quality pump that can support up to 600-800 horsepower.

The thread also discusses the importance of fuel pressure regulators and their role in maintaining the correct fuel pressure. It is suggested that a higher-spec fuel pump will cause the regulator to return excess fuel back down the return pipe, and this setup can be run long-term without issues.

In another forum, a user seeks advice on the minimum fuel pump requirements for their 1UZ engine conversion. A helpful response suggests comparing the fuel pressure of a stock MA70 7MGE Supra fuel pump to the Ford pump or the specifications of the Bosch 910 pump. The user ultimately decides to go with a 7MGTE (Toyota Supra Turbo) fuel pump, which is expected to provide sufficient flow for potential engine modifications.

It's worth noting that fuel pump voltage is just one aspect of fuel delivery and engine performance. Other factors, such as fuel pressure, regulator, injectors, and engine tuning, also play crucial roles in achieving the desired performance from your 1UZ engine.

Fuel line size

The fuel line size for the 1UZ engine depends on the model of the car and the year it was manufactured. For example, the 1993 SC400 has the fuel return line on the rear of the driver's side fuel rail, while the 1995 LS has the fuel line on the passenger side. The 1UZ-FE engine also has different fuel rail designs, with some being round and others square.

When it comes to choosing a fuel pump, it is essential to consider the minimum requirements. For instance, a stock MA70 7MGE Supra pump should be adequate for a standard engine, while a 7MGTE pump would provide around 30% more flow. If you are planning to modify the engine, a higher-flow pump, such as the Falcon or Bosch 910, may be necessary.

Additionally, the use of a rising rate regulator is recommended when boosting a motor with an NA ECU and no other fuel control. The stock fuel pressure for the 1UZ engine is 290 kPa (2.9 bar or 42 psi).

Fuel pressure regulator

A fuel pressure regulator is an essential component of a vehicle's fuel management system, ensuring the engine receives the precise amount of fuel it needs for optimal performance. These regulators are designed to maintain stable fuel pressure, preventing fuel starvation or flooding, and can be adjusted to achieve the perfect balance for fuel efficiency.

There are two common types of fuel pressure regulators: return style and blocking style. Return-style regulators, also known as "bypass" regulators, are widely used in performance fuel systems. They maintain fuel pressure by redirecting excess fuel back to the tank, reducing the pressure in the system. This type of regulator offers several advantages, including faster reaction to changes in engine load, more consistent and accurate fuel pressure, and reduced lean condition spikes. Additionally, it is easier on the electric fuel pump, resulting in lower heat generation, reduced noise, and prolonged pump life. However, a drawback of return-style regulators is the need for additional plumbing, as they require a return line with extra hoses and fittings.

Blocking-style regulators, on the other hand, do not have a return line and are typically used in stock fuel systems. They work by blocking the fuel flow when the pressure reaches the set level, preventing excess fuel from returning to the tank. While these regulators are simpler and more cost-effective, they may not provide the same level of precision and control as return-style regulators.

When it comes to the 1UZ engine, the stock fuel pressure is 290 kPa (2.9 bar or 42 psi). If you are considering boosting the engine or making modifications, a rising rate fuel pressure regulator may be beneficial. This type of regulator increases the fuel pressure in proportion to the boost pressure, ensuring that the engine receives the necessary fuel enrichment under boost conditions. However, it is important to note that the stock ECU and fuel injectors may have limitations, and you may need to consider upgrading to a standalone ECU or piggyback system for more precise fuel management.

Injector scaling

The first step is to determine if injector scaling is necessary. Injector scaling is only necessary if you run out of MAF or have extremely high cylinder loads. If your setup is stock, you should be okay without injector scaling.

The next step is to load the correct injector data with the stoich change for E85. Log your fueling/inj pw and make sure they are in the safe range and you don't run out of fuel pump.

In this example, we will be looking at a 2005 USDM STi. The only relevant mods are a K&N Typhoon and Perrin FMIC. The car is adding fuel, which means the computer is compensating for a lean condition. The injector flow scaling was increased by .5 cc/min increments, but there was no noticeable difference in the AF corrections.

The next step was to decrease the injector flow scaling instead of increasing it. At one point, 3 cc/min was added, and the car wouldn't start, so the value was reverted to .5. There was still no real difference. The scaling was increased to 508.25 cc/min on injectors that are supposed to be 500 cc/min.

In this example, we will be looking at a Subaru STi. We will be using EcuFlash for making our tuning changes and RomRaider for our logging. The two parameters we will be focusing on are the injector scaling value and the latency table.

The injector scaling value is displayed in cc's per minute (562 cc's per minute in this case). The latency table is a 3D table where the horizontal X-axis is the battery voltage and the vertical axis is the manifold pressure. The vertical axis, however, is not being used, as the 3 rows of data are the same. This system is manifold pressure-referenced fuel pressure, which means that as the manifold pressure goes up and down, so does the fuel pressure.

The key element is that this system should maintain a consistent differential fuel pressure, which is the difference between the fuel pressure above the injector and manifold pressure below. As we raise the fuel pressure or the differential pressure, the injector finds it harder to open and flow fuel, and hence our dead time or latency value increases.

Latency, dead time, or battery offset is the difference in time between the length of the pulse width that the ECU provides the injector and the length of time the injector is actually open and flowing fuel. If we don't account for this properly, it will bring in weird problems with our fueling, particularly as our battery voltage and pulse width change.

In this example, we will be looking at a Holden Commodore SS. We have a few parameters here for our injector control: our flow rate vs pressure, offset vs pressure vs voltage, and short pulse width adder. The flow rate vs pressure is essentially the injector scaling, telling the ECU what the flow rate of the injector is going to be relative to the pressure delta. The offset table is our injector dead time, and the short pulse width adder defines the difference between the theoretical perfect linear flow of the injector and the actual flow at very small pulse widths.

Tips for Injector Scaling

• It is important to have a known good calibration for your mass airflow sensor first. If you upgrade your mass airflow sensor tube and your injectors, you will end up in a situation where you've got an error between your commanded air/fuel ratio and your delivered air/fuel ratio, and you won't know where to correct it.
• The scaling numbers will be affected by ethanol content and fuel pressure. If you're going to be running a dedicated E85, that's going to massively affect the scaling number you need for your injectors.
• If you upgrade the fuel pump to a high-flow pump, you might find that it bumps up the base fuel pressure slightly, which then means that your injectors will flow a little bit more fuel.
• The process for injector scaling involves gathering two data points and using our logger to look at our closed-loop trims, which will allow us to assess the quality of our injector scaling. We want to look at two very different injector pulse widths – one at idle and one at higher load or higher RPM (part throttle).
• If our low and high pulse width tests both show positive trims, that means that the closed-loop system is adding fuel, so we are naturally a little bit lean. In order to add fuel, we want to reduce the scaling number, which tells the ECU that our injector is smaller, so it provides a longer pulse width to get the volume of fuel that it wants.
• On the other hand, if our low and high pulse width tests are both negative, this means that we are rich, and the closed-loop system is removing fuel. We need to increase the scaling, essentially telling the ECU that we've fitted a larger injector, so for the same volume of fuel that the ECU wants, it will provide a shorter pulse width.
• This is an iterative process, and you are not going to get this right in one shot. While latency has less effect on our fueling at higher load and higher RPM, there is still going to be some effect, so we need to check that our higher pulse width fueling trims are still on point.
• We can use the combined error to guide us on the magnitude of our changes. For example, if our trims at idle and our higher pulse width are all positive or all negative, we can use that error to make a relevant change to our injector scaling.
• We should be able to get our scaling, particularly at higher RPM, dialled in within one iteration.
• We can then start looking at our idle trims and latency table and start dialling in our latency. As mentioned, there is a bit of toing and froing with this, as every time we change the latency, we still need to check that our higher pulse width fuelling trims are still on point.
• When it comes to our latency values at different battery voltages, the technique of dealing with this is really up to the individual. Personally, when scaling injectors, I will just make an overall change to the entire table. The general shape of the table will not change, only the specific numbers.
• Our charging system in our car is designed to maintain our voltage pretty much bang on 14 volts, in fact, somewhere between 13.8 to 14.2 is where we normally are. So, 14 volts is the key critical column in this table that we want to know is right. If we find that we need to increase this entire table, we can just highlight the entire table and make that change.
• The alternative, if you want to be fussier, is to disable the alternator, pull out your alternator fuse, which will bring your voltage down to probably 12, 12.2, and then as the battery voltage drops down, you will end up down in this lower voltage area.
• Once you have your scaling within that +/\- 5% but ideally +/- 3% at both idle and higher RPM, you also need to test your wide-open throttle performance during a ramp run or at full-throttle acceleration run and log the air/fuel ratio.

Frequently asked questions