club.liberty.asn.au

Hi guys, so I've got the MY04 GT with an aftermarket fuel pressure regulator.
The car's been running rich for a while now and the guy I bought it off just mentioned today that maybe adjusting
the regulator could help. Problem is I can't seem to find what the pressure should be at idle and so I don't want to
just go around doing stuff willy nilly in case I lean it out too much, does anyone here know what it should be sitting
at?
I also read that cleaning the MAF sensor could help, is that a viable option? I haven't checked for air leaks as I'm
not really sure where to start with that.

Okay, the quantity of fuel injected into the engine is controlled by
[a] the "size" of the injector
[b] the duration for which the ECU holds the injector open
[c] the pressure across the injector.

The fuel pressure regulator controls the fuel pressure with reference to the manifold pressure.
As the manifold pressure drops (closing the throttle) the FPR will bleed excess fuel to the tank to maintain constant relative pressure across the injector.
As the manifold pressure rises (opening the throttle) the FPR will restrict the fuel returning to the tank, thereby increasing the fuel pressure to the inlet of the injector, again maintaining the relative pressure across the injector.

With constant relative pressure across the injector, the injector can then basically work just like a valve, and the quantity of fuel injected is proportional to the opening time of the injector.
So, higher fuel pressure regulator setting, more pressure, generally richer mixture.
Lower fuel pressure regulator setting, less pressure, generally leaner mixture.
However, see the section on fuel trim adjustment, below.

If your unit is running rich, then this can be caused by two things
{1] the manifold pressure sensing line may have dropped of the FRP and the fuel pressure can be too high at idle and would be too low under boost. (too low a fuel pressure under boost would be catastrophic)
or
[2] fuel pressure regulator could be out of adjustment.

The minimum you would need for a DIY diagnosis of fuel pressure regulator setting would be a scan tool to assess the ECUs present long term and short term trim values.
If the engine in genuinely running rich, the ECU would be trying to compensate by attempting to lean back the fuel mixture by adjusting the fuel trims.

One of the tuners on the forum may be able to advise what would be a "normal range" for fuel trims to be.

I have checked the factory service manual and the FSM does not give a "setting" for the fuel pressure apart for the minimum pump capability.
As described above, the Fuel Pressure Regulator will continually adjust the fuel pressure in response to the manifold absolute pressure.
Fuel pressure regulator would need to be adjusted against a know constant pressure - atmosphere.

Ok that's just confused the hell out of me. I might just have to get it on the Dyno at some point and have a professional do it.
Thanks for the info though.

You can't adjust the stock FPR - if you don't know what you're doing, have a professional do it.

Stock fuel pressure is 43.5 psi, set it to that.
Then pay someone to tune the car.

kiahatsiu wrote:Stock fuel pressure is 43.5 psi, set it to that.
Then pay someone to tune the car.

That's great information.
Thank you from everyone.

I would assume that this would be set with reference to atmosphere, that is, with the manifold pressure regulator vacuum hose disconnected?