Which is correct?
[Pump] - Rail] - [FPR] - [FMU] - [Return tank]
or
[Pump] - Rail] - [FMU] - [FPR] - [Return tank]
Im guessing it goes [FPR] - [FMU]
No its not, it says nothing about the FMU
I checked
What is a fuel system FAQ wrote:
Fuel system modifications
In the turbocharged kingdom, fuel is the king, queen, and town drunk. Most people will buy a fuel management unit (FMU), that goes in the fuel system and increases fuel pressure in a ratio with the amount of boost. Here is how an FMU goes in:
...--[Fuel Rail]--[FPR]--[FMU]--[Return Line]--...
Yes, the FMU goes after the FPR. (Ironically, in some fuel systems, the FMU completely replaces the FPR, this happens in the Hahn turbo kits for the Eco, but only because the FMU they picked also has a boost onset pressure, which regulates the pressure when you are not in boost as well). The FMU takes over after the FPR is fully open (in boost, you are making positive pressure, the FPR is maxed out at 0 PSI), and increases fuel beyond that, usually in a ratio with boost.
Now people who buy fixed rate FMU's are usually just buying the maximum ratio FMU they can buy, which really isn't all that smart. Buying a 12:1 FMU increases fuel pressure 12 PSI for every 1 PSI of boost, and it does this OVER stock pressure. So lets say your FPR at 0 PSI is putting out 55 PSI of fuel pressure, but you are boosting at 10 PSI with a 12:1 FMU... You are adding 120 PSI to your fuel system! This is WAY over the amount of pressure the pump is capable of supplying, and is WAY too much fuel for the injectors.
The best thing to do is to buy an adjustable FMU. These can adjust the rate, usually from 1:1 through 12:1 so you can pick and choose what the best ratio is for you.
Lots on the FMU, right from the FAQ...
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