Fuel pressure regulator with no vacuum line?

Hi everyone,

Got a friend of mine who's got recently a fuel pressure regulator without a vacuum line connected to the intake manifold.

If I remember it right, the regulator was connected to the fuel supply line and that's it, it had a gauge showing 4 bars at idle.

Basically i've got a few questions:

1. He's got a standalone ECU and a turbo engine, as far as I know, the fuel pressure should be around 3 bars in this case or the fact that he hasn't got a line connected to the intake manifold doesn't calculate the differential pressure? Correct me please if I got it wrong.

2. Is it ok to install a fuel pressure regulator that doesn't calculate the differential pressure, doesn't it mean that the pressure won't be constant in relation to the changes that happen in the intake manifold?

3. I am planning to get a custom fuel pressure regulator myself, on a budget for now, any recommendations please?

Thank you

That's a really bad idea for a turbo car. He will be loosing effective fuel pressure under boost conditions, and the ECU fuel mapping will need to compensate with a wider fuel pulse width, he could easily run out of injector in that scenario.

Fuel injectors are rated for the differential pressure -- that is the difference in pressure between the fuel rail (controlled by the pressure regulator) and the manifold that the injector is spraying into. As the manifold pressure rises the differential pressure will drop, unless the fuel pressure regulator compensates.

By referencing the fuel pressure regulator to the manifold pressure, the differential pressure will remain constant. So when the ECU wants 10% more fuel, it get's 10% more fuel with a 10% increase in effective pulse width.

If your regulator doesn't have a reference to manifold pressure (this is not uncommon in many normally aspirated cars), then the pressure changes are just "baked" into the fuel map. It does mean that the math to figure out the required fuel change to hit a desired Lambda/AFR value will be off, but usually a couple of cycles will get you on target.

So given a choice -- always use a fuel pressure regulator referenced to the manifold pressure.

Here is an article that clued me in years ago..

http://injectordynamics.com/articles/fuel-pressure-explained/

Thanks David for such a detailed and helpful answer!

Glad you found it useful.