increase fuel pressure in your fuel rail

[cortez]

Yes, I have done this mod. It's an old idea. The factory manual pretty much covers this.

I have never mentioned anything about idle. You confused my with someone else, I think.

I'm sorry about the "built" thing. I thought that the term was common enough everywhere.

The stock fuel pressure: Between 30 and 37 psi with engine idling and the hose connected. Between 38 to 46 psi with engine idling and hose disconnected, according to my manual.

The FPR increases the pressure in the rail as a function of decreasing vacuum. It is there to make sure that there is enough fuel available to the injectors under all loads without needing to change the rate of the fuel pump itself. It is a restrictor in the return path of the fuel back to the tank. (I'm sure you knew all this already )

The factory manual explains that pulling the hose should raise the fuel pressure in the rail to between 38 to 46 psi. It also explains that this is the pressure you should get at full throttle. This is why they have the procedure to test the regulator with the pulled hose.

This is what I have done myself: I have hooked up a fuel gauge and measured fuel pressure at idle and then at full open throttle. I have then diconnected the hose at the FPR. The result: The same pressure that I saw at full throttle is what I saw immediately at the FPR when I pulled the hose. No matter what the throttle position was. I am sorry that I don't have the exact psi numbers of that particular test with me, but I have them in the race car's logbook and I it is with the car, which is not at my house. That is all I can bring to the table as far as this discussion.

Anyway, look; I don't mean to offend you and I appologize if I was too enthusiastic in my responses. You should go ahead and try it yourself. It should be pretty easy to prove by hooking up a fuel gauge with a "T" to the fuel line. If you find that you are getting more pressure with the pulled hose than you get with it connected and the throttle wide open let me know because then I will be very confused as to why that would be the case and I am always interested in learning. I never have any problem admiting that I am wrong when I am. So, let me know, OK?
:D

[Protoss]

i will do that, i to do not have a problem being wrong and apologize if i also did offend but i prefer being corrected with hard facts. that is just the way i am.

i'll also test this while on a dyno. it might not do anything for top end but it would most likey be helpful in the mid ranges. that is where i am more intested.

[macklum]

This is how the how the fuel pressure increase happens, the vac hose that is attached to the FPR is also attached to a vac switch ,this switch is normally closed . when it is closed the Fuel pressure is around 37 psi . when you go to wide open throttle the vac opens the switch to allow the FPR to see atmosphere pressure . this causes the fuel pressue to increase to 42 psi . If you disconnect the hose and block it the Vac switch still works and the computer still thinks it is working as it should . The FPR is always open and the fuel rail is at 42 psi all the time ,This is why you can advance the static timing approx 5 degrees over stock settings and have no knock .
I found out about this on one of the Miata sites .

[cortez]

Originally posted by cablemirc
YUO GOT OWNED BY TEH BOOK

Yeah, it is not exactly zero, but it pretty much is zero for all practical purposes of the application. This is the difference between what we learn in school analyzing models and applying it to a real world situation.

When the throttle is completely open, the plenum becomes part of the atmosphere, as far as the car is concerned. Like having a bucket under the water. The combustion chamber becomes the plenum now and the valve becomes the throttle body. As far as vac. for the accesories, like the FPR, there is nothing.

All you have to do is hook up a vac. gauge to one of the plenum nipples, start the car, open the throttle all the way and read the gauge. Post here your results.

Go search on the web on "Vacuum at wide open throttle".

In any case, what we are interested in here is in how the FPR works, right?

when you go to wide open throttle the vac opens the switch to allow the FPR to see atmosphere pressure . this causes the fuel pressue to increase to 42 psi . If you disconnect the hose and block it the Vac switch still works and the computer still thinks it is working as it should . The FPR is always open and the fuel rail is at 42 psi all the time

Another example from the web on how FPR's work:
From http://www.240sx.org/
"Your car as well as most fuel injected cars have a one to one fuel regulator. It varies the fuel pressure by 'watching' manifold pressure. It uses a diaphragm to control pressure. Most Nissans at idle (vacuum) fuel pressure is 34psi and at full throttle (No vacuum in theory) 43psi. "

So, going by what macklum posted:
1) With the hose connected, at wide open throttle the FPR holds pressure at 42psi.
2) With the hose disconnected, the FPR holds pressure at 42 psi, no matter what the throttle is doing.

This is exactly what I said before.

So, if this is the case, what advantage are you getting by doing this mod over not doing this mod when you drive at wide open throttle?

At part throttle you would have more pressure with the mod than without, but at part throttle, the ECU is using the sensors to adjust the fuel back (up to a certain point).

[bruce95fmla]

shoot with these gas prices , my car doesn't need to burn more gas and not go much faster

[Protoss]

Originally posted by cortez
Yeah, it is not exactly zero, but it pretty much is zero for all practical purposes of the application. This is the difference between what we learn in school analyzing models and applying

where did you go to school?

[macklum]

no offense to those of you that are anyalizing this to death ,this is one of those thing that just works . All I know when I had this done the car ran better and used less fuel.

[Protoss]

Originally posted by cortez
Yeah, it is not exactly zero, but it pretty much is zero for all practical purposes of the application. This is the difference between what we learn in school analyzing models and applying it to a real world situation.

When the throttle is completely open, the plenum becomes part of the atmosphere, as far as the car is concerned. Like having a bucket under the water. The combustion chamber becomes the plenum now and the valve becomes the throttle body. As far as vac. for the accesories, like the FPR, there is nothing.

ok i know this is off topic and i will eventually start another thread elsewhere scream bloody murder on this point. just a heads up. there is a difference between what you are saying you "learned in school" and what actuallt ****en happens! but this is not the tread to speak of such a thing.

as for the fuel rail pressure WTF cares anymore. what point are you out to prove? macklum noticed better perfromance, ok deal with it. you disagree we know that. i believe you do know what you are talking about, to me the fuel rail issue is something i have to find out for myself.

as for your intake "theory" i question that.

Brock Robertson,
Aerospace IV: propulsion, engine performance, aerodynamics
Carleton University

[cortez]

Look, I really don't care if you do this or not. I was just trying to help you out save some time and money because I've tried this before. You already said that you don't believe that I am right and that you are going to try it. That sounds perfectly fine to me.

I don't see any reason to get upset. I'm not trying to attack you or anything like that and hey, now you have one opinion of someone that tried it and says it doesn't work and another one that tried it and says it works. I am not here to get into pissing contests and to discuss theory. All that I have tried to explain has been based on my own observations and there really is nothing else I can add to this. For all I care, my "intake theory" could be wrong. It doesn't matter because it doesn't change what I saw.