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The easiest way to increase fuel supply to any car is to increase fuel pressure. This article is focused on our beloved Lexus Flagship LS400 ( Celsior) and SC400 ( Soarer).
With low boost application, FMU ( Fuel Management Unit) is the easiest way to increase fuel supply to the demanding need from forced induction of Lexus cars. Most OEM fuel regulator also have similar to the a FMU. However, most are 1:1 ratio. 1:1 ratio means one pound of boost the FMU will increase one pound of fuel pressure.
For the Lexus V8 forced induction application we are aiming from around 10:1. Too much fuel pressure will have negative effects on the fuel system and fuel flow rate. Therefore, its not the more the better. Balance is what we are looking for. With less than 8 psi, we are pretty safe to use FMU.
The basic fundamental function of a FMU is to increase fuel pressure as the boost or positive pressure increased from forced induction like supercharging or turbocharging.
Please read more about the function of a FMU in here Function of FMU. There are many company makes FMU. Some of the popular makers are Vortch, Paxton and B&M. They all serve similar function.
However, I chose Cartech FMU not only its an awesome looking piece of art, but this baby allow adjustments. The range is from 4:1 to 12:1 and anything in between is fair game. As stated from the above link, the ratio is the boost pressure and fuel pressure.
Where to install the FMU? The 1UZFE setup is pretty easy. The FMU is used in the return fuel line. Return fuel is the fuel line goes back to the fuel tank. Most car have two fuel lines. One goes to the engine and other return the fuel to the tank.
Imagine this, if you put your thumb at the end of a garden hose, the water would increase pressure and spray further and harder. This concept also apply to the FMU and the function is pretty similar. For the U.S. 1UZFE ( I am not sure if the J-Spec are the same, therefore, I do not want to assume. You know what happen when we ASS U ME?
In the U.S. Spec Lexus LS400 and SC400, the return line is the easiest place to install the Fuel Management Unit is at the area of the master brake booster. Here are some pictures might help to locate the return line.
The brake booster area is a perfect location to attack this modification. Since the engine fire wall is angulated, you would need a L-Shape (90 degree angle) to mount the FMU.
The return line will be connect to the FMU and the second outlet will be continue the return line. Unless u know exact fuel/boost ratio, its always better to get a larger (higher ratio like 12:1) FMU and you always use a bleeder valve to lower the ratio. Its almost like a manual turbo boost controller.
The first picture is the location of the brake booster and the braided stainless steel fuel in is after market. OEM line run similar path. The connection is where the FMU to be connect. Remember to tight all the connections to avoid any possible fuel leak.
I hope you enjoy this brief crash course article on Lexus V8 like the LS400 and SC400 fuel management unit. Remember, this is for low boost application. This is not advisable for greater than 8 psi. With low boost supercharged or turbocharged application on Lexus V8, this will solve your fuel demand from forced induction.
The stock Lexus V8 Fuel System is designed for natural aspirated V8 engine and it works very well. However, if you are interested in forced induction like supercharging or turbocharging your Lexus like LS400 or SC400, then a adjustable fuel pressure regulator is very important. The stock provide around 28-34 psi of fuel.
Adjustable fuel pressure regulator (AFPR) allow adjustment throughout the range. Why is this FPR important? FPR allow fine fuel adjustment during idle. Secondly, non intercooled forced induction system would benefit much with greater fuel pressure to atomized the fuel and keep the combustion chamber cooler. Higher fuel pressure acts as a medium for cooling. Currently, I set my idle fuel pressure at 38 psi.
One of the easiest way to change from a stock FPR to an AFPR is to remove the oem RPR and replace it with afpr. However, there aren’t any bolt on AFPR. Some Supras might have the bolt on style, but I have seen one yet. Secondly, the bolt on AFPR might not fit perfectly due the location and the design of the engines are slightly different.
I am still looking for it and once I find it and I will let u know. Meanwhile, I used an universal AFPR from Aeromotive. This AFPR can handle over 1000 rwhp and its plenty for my setup. I also installed a fuel pressure gauge and I can feed back instantly.
Before you start messing with the fuel system. You must take precaution. Fuel is a dangerous chemical if it is not handle properly. The best thing is to let the car rest over night. The engine is cooled and the fuel pressure dropped to zero. Disconnect the battery and they you are set to go.
The first thing I did was to remove the OEM return fuel line banjo. I simply remove the nut and cut the return line. Do this slowly and you see some fuel leak out from the engine. Do not worry, since the fuel pressure drop to zero over night, it would not be much. Just some towels and prepare to clean it up. To install the new after market Adjust Fuel Pressure Regulator, I have to get a 10 mm adapter to 6-AN (Male to Male). I left the oem fuel regulator in place just incase one failed and second would still work.
In this setup (two regulators) the oem fuel pressure is the lowest fuel pressure I can set. The new regulator only good for after 34 psi. Confusing? the limiting factor is that the oem regulator is in front of the new AFPR and therefore the new regulator can only regulator pressure greater then the oem regulator. If this is confusing, you can remove the oem regulator and get a banjo with 6-AN.
I did this setup because its fail safe system. I mounted the AFPR at around the passenger side and connect the return fuel line to the driver side where I reconnect the new return line to the oem line. Pictures below will tell a better story and data from Lexus Repair manual.
FUEL PUMP PERFORMANCE
Application psi (kg/cm²)
ES250 & LS400 38-44 (2.7-3.1)
REGULATED FUEL PRESSURE
At Idle w/Vacuum At Idle w/o Vacuum
Application…………. psi (kg/cm²) ……………psi (kg/cm²)
ES250 ………………. 33-37 (2.3-2.6) …….. 38-44 (2.7-3.1)
LS400 ………………. 28-34 (2.0-2.4) …….. 38-44 (2.7-3.1)