39.69 psi is the target fuel pressure via the ECU. With high loads that you'll see with FI and nitrous, the ECU on the 2005 and newer Duratecs will target 53 psi of fuel pressure.

 

So 53psi for wet too or just for dry?

I'm using a wet system so the computer shouldn't be adjusting the pressure up to compensate cause the MAF never sees it right?

It works great now, but I just want to see about fuel jet swaps, etc. to make it work better. If the pressure changes..that changes some stuff..

 

Or I suppose what I mean to say, if the computer *thinks* it is running NA (sees normal atmosphere at the MAF) will it try to jump beyond the ~37psi?

Say, just under a WOT condition normally.

 

The fuel pressure will change according to calculated load. If your load goes up beyond a certain point, so will the fuel pressure.

 

"The fuel pressure will change according to calculated load. If your load goes up beyond a certain point, so will the fuel pressure." ..... OK, I understand this part. Above a certain calculated load threshold (based on airflow reading from the MAF sensor), the ECU steps up the fuel pressure to a higher theoretical target.... but exactly how does our returnless fuel system work?...

Randy, correct me if I'm wrong (I'm not all that familiar with returnless style fuel systems)...

I see a vacuum line connected from the intake manifold to the fuel pressure sensor located on the fuel rail. Based on the physical appearance of the sensor, it looks like fuel pressure acts on one side of a diaphragm, vacuum acts on the other side, and the combined force probably acts on a single load cell in the sensor housing (or some other similar way.) In short, the sensor compares fuel pressure with the air pressure in the manifold. Basically, this would be the electronic version of a vacuum-compensated mechanical fuel pressure regulator (FPR). In traditional MAF equipped applications with fuel injectors that are exposed to intake manifold pressures, this is done to vary the "base" fuel pressure (in our case, a "target pressure" of 39.69 or 53 psi, depending on engine "load") with the actual pressure in the intake manifold... as the pressure in the manifold drops, the FPR lowers fuel pressure... as pressure in the manifold increases, the FPR increases fuel pressure. This allows the fuel injectors to inject the same amount of fuel for a given pulse-width regardless of what the air pressure in the intake manifold is. I'm assuming our fuel pressure sensor is used to accomplish the same thing electronically.

So Randy... does our fuel pressure sensor in fact behave this way, and, thus, does the ECU adjust fuel pressure on the fly based on the air pressure in the intake manifold? Or something completely different?

 

So Randy... does our fuel pressure sensor in fact behave this way, and, thus, does the ECU adjust fuel pressure on the fly based on the air pressure in the intake manifold? Or something completely different?

Fuel pressure can be adjusted by the ECU due to many things. ACTs, Load, and Airflow to name a few on the 2005 and newer Duratec Focus.

 

What's "ACTs"?

Right... but asside from other special opperating conditionals in the logic (load, airflow), does the ECU primarily vary fuel pressure based on manifold boost/vac? I guess the better question to ask is... exactly why is there a vacuum signal supplied to the fuel press sensor?

 

mine sits ~53-55psi at idle according to my fuel pressure gauge...so uh..it's not supposed to do that?

 

Well did you ask for increased fuel pressure with your flasher? ^^^

 

Nope...I'm just rolling on my regular 91 octane tune..the only special options I asked on this tune was for a correction for my header and speed limiter removed. Unless you bump it up some on that tune anyway.

Haven't tried with my other tune (the stock timing -2 degrees one..the nitrous one basically). I haven't checked what that one is set for, but it should be stock cause I'm using a wet system anyway and it adds all the fuel I'll need..lol.

 

Did you order it from us? If so, give me your name and ECU code and I'll have a look.

Unless your fuel pressure was increased, you shouldn't be at 53 psi at idle. Either you have an inaccurate gauge or you have a problem somewhere.

 

PM sent.

Icky...I hope it is the gauge or increased pressure via tune, cause problem somewhere else sounds like no fun!

 

Fuel pressure gauge is teh culprit.

Hooked up my laptop and set that variable that you suggested and it was 39-40psi at idle.

Thx Randy!

Now I just need to buy a new gauge!

 

OK, good to hear.

 

So If I'm reading this correctly when the flash tune is set the xcal-II will increase my fuel pressure right! in reference to the forced air...or do I need to set the tune to do so?

 

No I they won't change the fuel pressure unless you really want them too.

My problem was a faulty gauge, and they way I got it totally figured out was by datalogging it through my xcal2. It showed the correct fuel pressure whereas my gauge didn't.