The probability is 100% that whoever installed your engine and EFI system did not install a PPRV. PPRV stands for "positive pressure relief valve." Basically, it's a check valve that goes between the fuel pump(s) and the injectors that prevents fuel drainback to the tank giving you quicker start-ups after the car has been sitting.
If you ever pushed the relief stem on an OEM EFI Schrader valve you will likely remember the squirt of gas that is emitted. The pressure that produced that squirt of gas does the same thing at the injectors at startup, initially fueling the cylinders for a quick start. If you do not use a PPRV then you need to do a key on but do not start the engine until the fuel pump(s) slows down, indicating the entire fuel delivery line is full.
You can find PPRVs from almost all AN hardware suppliers. They are just one-way check valves. The trick is getting one that is essentially invisible to the fuel pump's delivery process — i.e. low opening pressure, high flow and a good seal.
The best I've found so far comes from the Australian AN supplier,
Speedflow. This is a link to the valve I use, click here =>
Speedflow USA 610-10-BLK. They are not inexpensive but they do work and they provide a low, blow open pressure (around 3 to 5 psi) along with good sealing and fuel system back flow prevention performance.
The valve should be installed in the fuel system feed line as physically close to your fuel pump as possible The PPRV is supposed to help you prevent/mitigate the drainage of fuel in the fuel line back to the tank. The closer to the injectors you place it, the less effective it is. The closer to the tank (but after the fuel pump) you place it, the more effective it is.
Detroit uses in-tank fuel pumps and integrates its PPRVs into the fuel system right after the fuel pump, inside the fuel tank. The closer you can get to mimicking the OEM plumbing model, the closer you will get to OEM-style start-ups.
p.s. My fuel system uses a -10AN feed line. For a n/a application of around 7 liters, you can easily get by with -8 hardware instead of -10.
p.p.s. The other 100% you don't have it bet, I would make, is that the fuel system designer/installer did not install a Schrader valve on your fuel rails. It is a good bet that there is a ⅛" NPT port on one or both of your fuel rails that has a pipe plug installed in it instead of a Schrader valve. Take out the plug and put in a Schrader valve.
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