Fuel Pressure Regulator Vacuum Reference?

D

disquek

Well-known member
For those of you with ITBs (if you have a single TB, sorry - it's different), are you using a manifold vacuum reference to your fuel pressure regulator?

I've made a manifold vacuum manifold (of about 6 cubic inches) to dampen the signal, but I'm still concerned that the fluctuations in an ITB with a big cam will result in erratic fuel pressure.

This may only apply to GT folks. I'm not sure if many prod cars can run ITB fuel injection.

-Kyle
 
What's your base system fuel pressure? I can't imagine that you would need to adjust your fuel pressure that much if you have EFI already--- Carb would be a different issue since pressures are so low.

Instead of fiddling with pressure, could you just increase/decrease injector duty cycle and keep a constant fuel pressure?

Do you have any sort of crossover tubes between intake ports to equalize pressure between them? I'm not sure if that would help or hurt the issue if you have one throttle body that's out of whack compared to the rest.
 
I have ITBs on my Mazda MZR engine used in my Prototype 2 sports racer. I pick up the manifold pressure and use that as the reference pressure for the fuel pressure regulator. The reason you want to do that is because the flow through an injector is mostly linear relative to the differential pressure across the injector (ie Fuel Pressure - Manifold Pressure).

If you do that, then the mapping of the ECU is somewhat simplified, as the fuel delivered will be as you expect relative to any manifold pressure.

Now if you don't reference the fuel pressure to the manifold pressure, then you can still map the ECU and basically "bake-in" the manifold pressure changes at a given throttle position.

I don't use a large vacuum manifold, only equal-length vacuum hose connected with T-connections. I think my passages into the manifolds are only about 0.030" or so.

Here's a great article from the Injector Dynamics website on Fuel Pressures:
http://injectordynamics.com/articles/fu ... explained/
 
Thanks David,

That's a great article for explaining the basics of this.

My question is about the "lumpy" vacuum that, if fluctuating up and down, will cause the fuel pressure to fluctuate similarly.

Would it be easier to use the ECU to map around this issue, or allow the FPR to do it mechanically?

I'm guessing that this is an "it depends" answer based on the characteristics of the individual engine.

-Kyle
 
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