Fuel Pressure

[Brutus]

Can anyone tell me what the fuel pressure should be at the fuel rails on a N/A Marauder? Should it be different (higher) when using a power adder?

[BillyGman]

Can anyone tell me what the fuel pressure should be at the fuel rails on a N/A Marauder? Should it be different (higher) when using a power adder?I believe that it depends what power level you take it to. The stock fuel pump and fuel pressure as far as I know, is said to be good for up to atleast 430 RWHP. The thing that's definately required is the use of bigger fuel injectors. The Trilogy kit I installed on my car came with bigger fuel injectors, and a fuel pump amplifier which directs more electrical current (I believe more amps) to the stock fuel pump. However, I don't think think that it increases the fuel pressure. It simply ensures that there isn't ever a voltage shortage at the fuel pump, since that would be possibly dangerous for a supercharged engine.

[Tinaree]

To expand on what BillyGman said, your injectors operate within a safe duty cycle range, and the amount of fuel is determined by the pulsewidth (how long it is open) controlled by the PCM. For a specific injector size, the amount of fuel (by weight) can be increased or decreased by adjusting the pressure, or by adjusting the pulsewidth, or both.

On the previous generation 4V engine, the fuel rails were kept at a constant pressure by means of a mechanical fuel pressure regulator which bleeds extra pressure back into the tank, and the injector pulsewidth varied to control the fuel. Simple to work with. I mention this because what works on these engines does not necessarily work on the Marauder.

The new 4V engine, like in the Marauder, varies not only injector pulsewidth, but also fuel pressure. In Billy's kit, the amplifier he mentioned does increase the maximum fuel pressure available at the pump, by raising the operating window of the fuel pump. Just adjusting the pressure in the PCM only gets you to the maximum pressure of the pump; his unit raises that maximum.

I don't know what pressure should be at idle, but it needs to vary anyway. I think I'll look at this the next time I hook up the autotap.

[Brutus]

To expand on what BillyGman said, your injectors operate within a safe duty cycle range, and the amount of fuel is determined by the pulsewidth (how long it is open) controlled by the PCM. For a specific injector size, the amount of fuel (by weight) can be increased or decreased by adjusting the pressure, or by adjusting the pulsewidth, or both.

On the previous generation 4V engine, the fuel rails were kept at a constant pressure by means of a mechanical fuel pressure regulator which bleeds extra pressure back into the tank, and the injector pulsewidth varied to control the fuel. Simple to work with. I mention this because what works on these engines does not necessarily work on the Marauder.

The new 4V engine, like in the Marauder, varies not only injector pulsewidth, but also fuel pressure. In Billy's kit, the amplifier he mentioned does increase the maximum fuel pressure available at the pump, by raising the operating window of the fuel pump. Just adjusting the pressure in the PCM only gets you to the maximum pressure of the pump; his unit raises that maximum.

I don't know what pressure should be at idle, but it needs to vary anyway. I think I'll look at this the next time I hook up the autotap.
If the pressure varies then what is the operating range? On supercharged cars is the stock fuel pressure regulator retained. Does the increased fuel come only from larger injectors and/or changing the pulse width?

[Tinaree]

I don't know the range. That is why I want to put it on the Autotap. I may need newer software, this version is well over 6 years old, but it took the VIN with no problems.

The regulator, I think, is all contained in that box underneath the fuel tank. It is controlled by the PCM. It is returnless. Obviously the Trilogy kit retains the stock unit from what Billy says. To answer your last question, the larger injectors allow more fuel, but they have to have more flow pressure at high flow ranges, and at low pressure stock settings (idle for instance) they may not be effective. I really don't know much about the tuning on these, it might be that Trilogy maxes the pump and controls it all via pulsewidth, but I doubt it. That would be pretty inefficient. You could ask them.

[sailsmen]

http://www.kennebell.net/techinfo/general-info/BAPtheory_kens.pdf
http://www.babcox.com/editorial/us/us50146.htm

The above links will help.

The stock fuel rail pressure sensor is retained. There is no "fuel pressure regulator" per say.

30psi @idle and 40psi @ WOT.

[Brutus]

30psi @idle and 40psi @ WOT.Thanks- thats what I was looking for!

[SergntMac]

Thanks- thats what I was looking for! Sailsman is correct, it's a returnless system, so, no regulator, just a rail sensor. My last tuning event this past April showed 35 PSI across the injectors @ 6000 RPM. 42# injectors, Walbro 255L pump in the gas tank, Reinhart in-line fuel filter with -8 lines in between. Hope this helps.

[Tinaree]

So no one gets confused by my post, where I used the term "regulator" for the Marauder, it is really more appropriately called an electronic fuel pump control. The pumps are still DC though.