The MR1 Fuel Injection System Function

[Konnie]

Ask:
Explanation of the MR1 Fuel Injection system, including the purpose of the bypass valve and its motor and how the pressure is regulated.

Background:
As I strongly suspect that something is wrong with my 2006 Yamaha AR 230 Fuel Injection System I plan to diagnose it by adding fuel pressure gauge(s) and use the YDS app.
But before I attempt performing the diagnose I want to make sure I completely understand how the MR1 fuel injection system works.
I've done a bunch of on-line reading, searched this site and watched YouTube videos regarding the principals of fuel injection (mostly conventional) but I still don't have a good understanding of the MR1 fuel injection system.
How is the fuel pressure controlled? With the bypass valve?
There is no return line to the tank!
Here is a link to my thread that leads me to believe that I have an issue with the fuel injection.

https://jetboaters.net/threads/mr1-engine-not-running-more-than-6-000-rpm-at-times.37218/post-635849

Any help is greatly appreciated!!!

 

[84rzv500r]

the bypass valve has nothing to do with Fuel Pressure it is more like an Idle Air Control valve as it allows air to bypass the throttle plates which on an MR1 are not servo controlled but mechanical. The ECU uses the bypass servo to add more air and it adds more fuel when the ECU is commanded into either no wake mode or off throttle steering system to raise RPM's to a preset value and maintain. The fuel pressure is a deadheaded rail at ~47 PSI that is provided via the in tank fuel pump regulator assembly. what fools everyone is that the return is in the tank. the ECU turns on the fuel pump relay at key switch on and if it doesn't detect a running engine it turns it off until the engine is running.

@Robb235 has some great posts from his MR1 XR1800 build and I have some of this documented in 2004 AR210 repower with MR-1 HO's

 

[Konnie]

This is a great help! Truly appreciate the explanations!

 

[Beachbummer]

Oreilly or AutoZone will loan you a gauge with a T and some clamps that you can add in line to test pressure.

Mine was dead on at 50psi.

Is it one engine or both? With a barb and a length of hose you can swap the fuel engine inlets and test if the problem migrates with the pump swap.

 

[Konnie]

Thanks!
The only issue is with the port engine.

 

[v4tuna]

Thanks!
The only issue is with the port engine.

Did you get this resolved

 

[84rzv500r]

I haven't had time to get to it... I have a couple spare gear reduction units.. Its on the list