I've been thinking about an FPR for a while now, but always reach this conclusion. I am no expert on fuel systems but if I am to understand correctly.

1. Honda FPR non adjustable delivers a certain pressure lets say 41 with a variable of 7 as i've heard.

Meaning?
Either a) the pressure is not constant and varies those 7 while driving. Or b) came from factory running lets say at 45 but remains a constant?

2) If people buy an apexi f/con. How does this affect actual fuel pressure? I understand software for maps etc but don't understand how an ecu can replace a physical part which builds pressure in your line. Am I wrong about this?

If the answer is what I think it is , then an fpr's real benefit lies in keeping fp stable and constant. But it seems remarkable hondas fpr can't. I'm confused...

 

I think we've got the situation in your 1(b). So it's able to regulate efficiently it

 

Ok, the fuel pump pumps the fuel from the tank. It builds up pressure in the line to the fuel rail. At the end of the fuel rail is the FPR. The FPR has a diaphragm that opens when the fuel pressure reaches the desired level, thereby bleeding off the pressure into the fuel return line back to the tank. The injectors are on the fuel rail (before the FPR and return line) and, in theory, the fpr should keep the pressure in the rail pretty constant. The v-afc, f-con, and all those fuel computers work by shortening the pulse time of the injectors so that they simply stay open for less time. An fpr attacks the problem by keeping the pulse width constant, but varying the fuel pressure and thereby the amount of fuel sprayed during the pulse.

HTH.

 

I think I understand what your saying. I have a mugen ecu which has a preset map for fuel pressue, and what you are saying is

rev-"An fpr attacks the problem by keeping the pulse width constant, but varying the fuel pressure and thereby the amount of fuel sprayed during the pulse.

both achieve the same result (in theory) by different means. One mechanically and the other by management. So by adding an FPR to an perf ecu equipped car should be the best of both worlds then?

 

[QUOTE]Originally posted by viscreal2000
[B]both achieve the same result (in theory) by different means. One mechanically and the other by management. So by adding an FPR to an perf ecu equipped car should be the best of both worlds then?

 

remember that an ECU doesnt change pressure, just pulse duration and timeing. Also the ECU changes its curves slightly except at WOT so the FPR is really only good at WOT?

Is that right?

What I mean is the 'Adjustable' FPR is only good at WOT if we gain by going leaner, or being more precise.



[Edited by cmnsnse on 02-13-2001 at 08:48 AM]

 

In my experience, changing fuel pressure in small increments has little or no effect on part throttle, low rpms response as the ecu will take readings from the O2 sensor and adjust the mixture back to what it was supposed to be from the factory. However, at full throttle OR beyond a set rpm point (probably around 5000 rpms on this motor, but I'm not sure) the ECU will just run off the pre-programmed maps, so your ecu will let your fpr adjustments through.

but for fine tuning, I suggest the v-afc as it will let you fine tune for specific rpm ranges. An fpr will basically lean out everything or richen everything. You'll need dyno time for either one.

 

Two things:

1. The variability of the stock fuel pressure regulator happens two ways. One is the natural variation from regulator to regulator in spring pressure on the diaphragm which regulates fuel pressure. The average batch of Honda FPRs probably varies less than +/- 1-2 psi. The ECU can more than make up for this by adjusting pulsewidth (a 1 psi differential with a 45 psi ideal pressure would result in fuel delivery being altered by about 1.1%

The second variability, as one poster pointed out, is due to the vacuum line attached to the FPR. This doesn't mean fuel pressure goes up though as manifold pressure increases (or more appropriately manifold vacuum decreases). Rather (and I think someone else posted this somewhere) it makes sure that the differential pressure between the fuel rail and the manifold is constant.

2. Reverend is right about the ECU compensating at part throttle for any fuel pressure change. But the ECU has to apply what it learns at part throttle to the full throttle maps too. Otherwise, there would be no way to gain all that power from bolt-ons and breathing mods from Hondas with stock ECU and fuel systems. Think about it, a typical B16A can gain 15-20% torque across a wide rpm band with typical bolt-ons and cams. That would require a lot more efficiency, a lot more fuel, a leaner overall mixture, or, most likely, some combination of the three which, IMO, means the ECU is adding fuel at full throttle.

That's why I like the idea of the AFC-VTEC from Apexi. It has a part throttle map and a full throttle map. That way the ECU won't "unlearn" your ideal full throttle maps while you're driving around at part throttle.

UL

 

This kinda goes along with a previous post, but who knows or can find out the specifics of what the computers in this car can do? I mean not just the ECU programming and variability, but what it remembers . . .

But before anybody can make too much of a claim we need to know exactly what the ECU does and when, like when it switches to WOT operation, and what is entailed in the maps, as Im sure its more complicated than my older ECU's that I have used.

Im already getting a TEC-II programmable ECU for another engine, but Id like to be able to read programs from my other ECU's . . .