fuel pressure regulator

[ucancallmedebo]

An AFPR is even more important if your car has cams because the vacuume is lower at idle. Because of this the stock regulator will not take away the correct 9 lbs pressure. My vac at idle is -10 with webcams. This means that the factory reg is only pulling 5 psi off the base. This effectively would make me run richer even without a fuel system upgrade.Plus the fact I have a 255 rewired with 10 gauge my base is 48psi at idle with the vacume hose on and goes a little higher with it off. Yea the car drives, but at most any Rpm or light load where the motor is using very little fuel the factory fpr is unable to bleed of the extra pressure. Only at high loads in the upper RPMs does my motor take away enough fuel pressure from the rail for my factory FPR to maintain the correct pressure. My AFPR is still on backorder. I got so much rich knock at throttle tip in I cant even enjoy driving my car so it is parked. Anyway, my fuel pressure should be like 37.5 or so at idle right, not 27. There is no way for me to compensate for my low vacuum correct. I could lower the base to get it near stock but when it transitions from vac to boost I would be starting off to low say 27+18psi boost= 45 way to low for 18psi boost. Basicly if your car is running less than stock vacuum a afpr will not make it completly right and you will have to put up with the slightly higher base pressure at idle cause you should start at 38 on 1g. 02 sensor will take care of this though, or safc at 1k. Regardless, get a FP gauge. I got mine on the fuel filter for 35 bucks. screwed right into that little plug in the bango bolt. 37.5 on stock pump, 48 now . 38/ 48 = .791667 . 20% richer. :thumbdown "got knock"

 

[steve]

An AFPR is even more important if your car has cams because the vacuume is lower at idle. Because of this the stock regulator will not take away the correct 9 lbs pressure. My vac at idle is -10 with webcams. This means that the factory reg is only pulling 5 psi off the base. This effectively would make me run richer even without a fuel system upgrade.

You seem to have a common misunderstanding about why the FPR works the way it does.

We use a 1:1 rate FPR to keep the pressure difference across the fuel injectors constant so the amount of fuel an injector delivers per unit of time also remains constant. So as long as your FRP is regulating the pressure correctly that fact that you have low vacuum isn't the issue. Having FPR overrun messes the AFR up because the injector no longer deliver the same amount of fuel of the same opening time.

Steve

 

[ucancallmedebo]

I know we have a 1 to 1 riseing stock but I was under the assumption when under vacuum the regulator subtracted pressure at a rate of .5 psi for every 1 hg of vaccum. This means that is you have less vacuum that you will have more fuel pressure. If the factory FPR does not subtract pressure under vacuum then It wouldent make a diffrence yes you are right on that, but from my own exsperience with my car the fuel pressure rises when the vacuum/boost refrence hose to the factory FPR is taken off at idle. If the regulator was solely boost only then why is this? Correct me if I am wrong but this was the impression I was under.

 

[steve]

If the regulator is regulating and not overrunning you will have the same fuel pressure at 10 in hg vacuum with cams as you would at 10 in hg vacuum without cams.

Like I said the FPR tracks manifold pressure to maintain a constant pressure difference across the injectors. Fuel pressure = Base pressure + Manifold pressure. So, at 10 in hg and a 36 psi base the fuel pressure = 36 + -4.9 or about 31 psi. The difference in pressures across the injectors is 36 psi. At 10 psi boost the fuel pessure is 36 + 10 = 46 psi but the difference across the injectors is 36 psi. The fact that you have low vacuum at idle isn't an FPR issue. The injectors will deliver exactly the same amount of fuel in say 2 ms as they would if you had 18 in hg vacuum at idle.

The point is as long as the FPR is working, it's not the cause of being rich. It's the fact the the ECU isn't programmed for an engine with cams like you have and if your FRP is being overrun by a big fuel pump it's no longer regulating.

Steve

 

[ucancallmedebo]

I see what your getting at now I was thinking in terms of no overrun but I do have that. Mines definately overrun the fuel pressure pulses with the alternator now. Guess I'll wait some more on the APFR to get instock.

 

[red93tsi]

Ok, I read most of this, but it's alot to think about at once, so I'll ask a specific question.

I have a 190 lph, 580cc's, etc. in a 1g, which according to one post on here should raise the base pressure about 3 to 5 psi over stock (36 psi) correct? So if I put in an auto or non turbo fpr which is rated at 43 psi, I would obviously have to re-tune the afc, but the higher base pressure rating of the fpr should be able to handle the increase created by the fuel pump, right? Basically would a stock 43 psi 1g fpr and a 190lph be able to maintain steady IPW maps?

See where I'm coming from as far as cost effectivness.

TIA

 

[red93tsi]

bump^^^^^^^^^^^

 

[Coup D E'Tat]

You've been here long enough to know that there is no bumping, but I'll answer anyways.

To my understanding, the NT regulators are not 1:1 risers, and would be useless on your car.



-Jesse

 

[mavisky]

If you bump again, there will be consequences.

A 2.0 nt regulator rises 1:1, I've tested and proven it.

 

[red93tsi]

Bah, It's been 3 days. As far as the nt fprs go I was always informed they had the same 1:1 ratio. Can anyone clear that up? And possibly answer my original question if the ratio is correct>

 

[red93tsi]

If you bump again, there will be consequences.

A 2.0 nt regulator rises 1:1, I've tested and proven it.

Thanks,

What about this one?

So if I put in an auto or non turbo fpr which is rated at 43 psi, I would obviously have to re-tune the afc, but the higher base pressure rating of the fpr should be able to handle the increase created by the fuel pump, right? Basically would a stock 43 psi 1g fpr and a 190lph be able to maintain steady IPW maps?

 

[Coup D E'Tat]

A 2.0 nt regulator rises 1:1, I've tested and proven it.

Well that blows my theory to shit

 

[steve]

A 2.0 nt regulator rises 1:1, I've tested and proven it.

Of course they are, for that same reason that a turbo one is. To maintain a constant pressure difference across the injector so that it sprays the same amount of fuel for a 2ms pulse at 18 in hg as it does at 0 in hg.

I can't answer the question about overruning the NT FPR with a 190l/h pump because I've never tried it.

Steve

 

[mavisky]

Thanks,

What about this one?

You really shouldn't need to re-tune, maybe a slight adjustment at the top end, but we're not talking another 50cc worth of fuel due to the slight pressure change. A 190lph shouldn't give you any troubles at all on that regulator. I ran a 300gt vr-4 pump (about 180lph un-re-wired) on the nt fpr and ran my lowest et yet on that combo

 

[awdsm drft]

Refresh me.

What's the benefit of a non turbo fpr? I've heard of this.

 

[mavisky]

Slightly higher base fuel pressure, rises 1:1 like a turbo regulator, extremely cheap, poor man's way to run a little more boost without having to upgrade injectors or some other fuel part.

 

[red93tsi]

Thanks mavisky. I was actually looking for a little different answer though. Earlier in this thread they stated that even the vr4 180lph pump would raise base pressure a few psi on the stock regulator, and I was just wondering if the n/t would combat this due to the higher raitingl. Or would it simply raise the pressure on the n/t reg too?

 

[mavisky]

You'd probably still see a slightly higher base fuel presure, I believe mine used to sit around 46 psi with the hose off on the nt regulator.