Reading some of the comments above makes me think that there is some confusion as to what changed on the later model FJR fuel systems.
The part 19 in the diagram mentioned above is the fuel pressure regulator as installed on the 03/04/05 bikes. It is vacuum referenced. The regulator has a diaphragm inside the can that is spring loaded to set the fuel pressure that the regulator "pops off". The vacuum signal modifies the spring load on the backside of the diaphragm such that the fuel pressure tracks intake vacuum. Excess fuel is returned to the tank. In this system the fuel pressure drop across the fuel injector is always constant. Fuel pressure varies constantly vs. the intake vacuum to maintain this.
The 06/07 bikes do not have that fuel pressure regulator nor do they have the fuel return line. Instead, there is a fixed fuel pressure regulator at the fuel pump so as to maintain a constant fuel pressure delivered from the tank to the rail. The pump still pumps the same volume and excess fuel from the regulator is still returned to the tank. Just the regulator is located immediately at the tank. The part #19 does not exist on the later model rail at all. The fuel flow is simply dead headed at the rail with no return line to the tank. In effect, you could run the 06/07 systems with the same fuel pressure regulator mounted at the tank instead and just leave the vacuum line off. Same sort of hardware just the location is changed.
Typically, port fuel injection systems have always relied on a constant fuel pressure drop across the injector. That way the only variable affecting fuel flow is how long the injector is opened...often referred to as the pulse width or the length of time the injector is pulsed open by the ECM. Since the tip of the injector is seeing vacuum (and the vacuum is changing with the engine operating conditions) the fuel pressure regulator is referenced to intake vacuum. Put a fuel pressure gauge on those systems and you will see the fuel pressure rise and fall with the changes in intake vacuum.
With the returnless systems the equation gets much more complicated since the fuel injector on time or pulse width is not the only variable affecting the amount of fuel delivered. For the same pulse width the injector will deliver more fuel at high vacuum than low vacuum due to the change in pressure drop with fixed fuel pressure. The ECM must not only calculate the amount of fuel to deliver but then make a secondary "adjustment" to the pulse width calculated to compensate for the fuel pressure drop across the injector at that instant. Anyone who thinks the ECM might be "slow" is barking up the wrong tree......
This all works fine....theoretically. The problem that surfaces, not so obviously sometimes, is that when one injector opens and closes it sends pressure waves thru the fuel rail. That is the water hammer effect mentioned in other posts. If the pressure spike in the rail happens to coincide with the opening or closing of another injector it was affect the fuel delivered without the ECM making any sort of compensation. This phenomenon is pretty difficult to pinpoint as the RPM and load it happens at and the cylinder(s) affected will change constantly. Most (all??) returnless systems that I have seen in the industry have a fuel pressure accumulator on the fuel rail to act as a damper to minimize or eliminate this water hammer effect. Especially 4 cylinder engines. Some V8's have a damper on each fuel rail to dampen the pulses from the 4 injectors on each side. Looking at the parts diagram for the 06/07 Yamaha I don't see a fuel pressure damper on the rail. Hmm..... Makes you wonder.......
The part 19 in the diagram mentioned above is the fuel pressure regulator as installed on the 03/04/05 bikes. It is vacuum referenced. The regulator has a diaphragm inside the can that is spring loaded to set the fuel pressure that the regulator "pops off". The vacuum signal modifies the spring load on the backside of the diaphragm such that the fuel pressure tracks intake vacuum. Excess fuel is returned to the tank. In this system the fuel pressure drop across the fuel injector is always constant. Fuel pressure varies constantly vs. the intake vacuum to maintain this.
The 06/07 bikes do not have that fuel pressure regulator nor do they have the fuel return line. Instead, there is a fixed fuel pressure regulator at the fuel pump so as to maintain a constant fuel pressure delivered from the tank to the rail. The pump still pumps the same volume and excess fuel from the regulator is still returned to the tank. Just the regulator is located immediately at the tank. The part #19 does not exist on the later model rail at all. The fuel flow is simply dead headed at the rail with no return line to the tank. In effect, you could run the 06/07 systems with the same fuel pressure regulator mounted at the tank instead and just leave the vacuum line off. Same sort of hardware just the location is changed.
Typically, port fuel injection systems have always relied on a constant fuel pressure drop across the injector. That way the only variable affecting fuel flow is how long the injector is opened...often referred to as the pulse width or the length of time the injector is pulsed open by the ECM. Since the tip of the injector is seeing vacuum (and the vacuum is changing with the engine operating conditions) the fuel pressure regulator is referenced to intake vacuum. Put a fuel pressure gauge on those systems and you will see the fuel pressure rise and fall with the changes in intake vacuum.
With the returnless systems the equation gets much more complicated since the fuel injector on time or pulse width is not the only variable affecting the amount of fuel delivered. For the same pulse width the injector will deliver more fuel at high vacuum than low vacuum due to the change in pressure drop with fixed fuel pressure. The ECM must not only calculate the amount of fuel to deliver but then make a secondary "adjustment" to the pulse width calculated to compensate for the fuel pressure drop across the injector at that instant. Anyone who thinks the ECM might be "slow" is barking up the wrong tree......
This all works fine....theoretically. The problem that surfaces, not so obviously sometimes, is that when one injector opens and closes it sends pressure waves thru the fuel rail. That is the water hammer effect mentioned in other posts. If the pressure spike in the rail happens to coincide with the opening or closing of another injector it was affect the fuel delivered without the ECM making any sort of compensation. This phenomenon is pretty difficult to pinpoint as the RPM and load it happens at and the cylinder(s) affected will change constantly. Most (all??) returnless systems that I have seen in the industry have a fuel pressure accumulator on the fuel rail to act as a damper to minimize or eliminate this water hammer effect. Especially 4 cylinder engines. Some V8's have a damper on each fuel rail to dampen the pulses from the 4 injectors on each side. Looking at the parts diagram for the 06/07 Yamaha I don't see a fuel pressure damper on the rail. Hmm..... Makes you wonder.......
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