Joeker

The gauge on a AFPR is not reading the manifold pressure, it is reading the fuel rail pressure.

Example, an engine is boosting at 1 bar, and base fuel pressure is 2 bar, that does not mean the gauge on the AFPR will read 3 bar.

Fuel pressure and boost pressure do not increase/decrease proportionately.

     

FatAssRubber

oopss...

Joeker's is right .. my mistake that i did not make it clearer.. the gauge will read the same because it is gauge pressure not absolute pressure.

The regulator is actually measuring the Pressure differential between fuel rail and exit of injector. Not fuel rail pressure.. errr.. this is getting too confusing.. i need my dinner first..

     

Joeker

I think the figures you quote are the rising rate ratio.

When at WOT or boost pressure, the AFPR is fully closed therefore the amount of fuel pressure is govern by the fuel pump,fuel rail dia., fuel hose dia. injector duty cycle, etc rather than AFPR

Fundamentally, AFPR is just a pneumatic valve.

This valve is controlled by the Manifold pressure.

At iddling where vacumn is highest, this valve is fully open and thus allowing most fuel to return to fuel tank.

As manifold pressure drops, the valve closes down and less fuel is
returned.

At WOT, fuel pressure will be highest regardless of NA or Forced induction, almost no fuel is returned because the AFPR valve is fully closed.

     

speedchaser

At WOT, fuel pressure will not be at its highest and some AFPR will not be fully closed. Just do a very simple experiment. With the vac unplug on the AFPR and the fuel pump voltage constant, use pliers and incrementally clip the return line and you'll see what kinda fuel pressure it'll shoots up to on a rising rate AFPR. That's how I do simple fuel pump and reg diagnostics.

On a rising rate reg, it will shoots up in pressure depending on your reg rate and fuel pump. On a strong pump, in excess of 7 bar is normal.

Or better still, log it with an internal fuel gauge on your dash with boost pressure.

     

Joeker

speedchaser,

Pls read carefully.

     

Joeker

Do you mean, OE regulator are not rising rate?


Excess of 7 bar normal? On another note, volume is more important than pressure, 7 bar is overkill and there is risk of jamming the injector pintle.

If the engine is not getting enough fuel even after fuel pressure is bumped up, then it is better going for larger fuel rail and injectors and fuel pump.

The adjustable fuel pressure regulator can only do so much.

     

speedchaser

Yep, I did read it properly. Just that what I was saying is that it will not be at its "highest" at WOT. Or I should have said might not be at its highest. I'm not disputing your "almost".

What I meant was on my simple diagnostic was that it could shoots up to 7 bar and it's normal for some reg but I don't mean that it must be at that pressure when it runs even on boost. It won't even reach that pressure. I'm only giving a point of reference for diagnostic on the reg and pump on whether it's performing as it should.

Any tuner worth his salt will know that volume is more important but pressure is also an important part of the configuration to get that fine mist for a complete burn.

Yes, on your statement that when we are not getting enough fuel even after pressure is bumped up, then go for larger injectors. I totally agree with that. That's what I have been doing all this while when I do my tune. I've never advocated changing to any adjustable FPR if possible, because I consider that as a band-aid to a properly tuned car. But I've received so many "ricer" cars that was changed before the tune and I have to work with that. Yet some of them have to be reverted back to the stock reg because a lot of those "China-made" POS is causing more problems then it's helping. A set of larger injectors to a certain degree and a good pump is the way to go with the aftermarket ECU.

I guess this thread is going off tangent from adjusting FPR pressures. But it's good banter and I think more thread should be like this. Thanks for the all the "technical stimulation" Joeker. :)

Signing off..

     

FatAssRubber

I think we need just to remember... What we want to achieve is a steady Pressure Differential across the fuel rail through injector into the manifold. Let's call this P1

Fuel Regulator is Dynamic valve controlling P1 by applying manifold pressure on the diaphram. Let's call manifold pressure P2.

The third pressure is P3, which is the fuel rail pressure.

Mathematically "if" i am getting this right is P3-P2=P1

P1 is set at idling when we know P2 is at 0 value. At that point, P3, Fuel rail pressure is same as P1.

So... P3 is a variable. So is P2, but P1 need to be constant. That's the whole point of the regulator.

Whether it is at WOT, or highest at certain point can be true, but only circumstantial condition. Not absolute.

Rising Rate should be exactly as manifold pressure. I found out that a lot of cheapo' regulator is not. Speedchaser will know this first hand.. i have had at least two that i can donate for charity or scrap. Still shiny and both within 6 hours operation.

I think what speed chaser is trying to get when he say it bumps up to 7 bar is that he does that to check if the pump is able to push pressure above workign pressure. As normal, any engineered product is design with the safety factor of 2, therefore if the pump can push to 7 bar, i would say max working pressure is 3.5 bar. Please note this is P3. NOT P1.

So.. sit back.. chill and just drive lah bro.. what you and i want is just to shred rubber .. nothing to do with pressure... wanna think pressure better go take out the "R" from drive and go dive instead.

:)

     

renxun

you are right there fatassrubber regarding the P1, P2 and P3.

joeker is right too ... no way a street car performance pump could give any more flow at 7bar.not my bosch 044 or my previous 2 units of 910. im not sure if there is any super duper hyper performance pump that would give at that pressure level. bosch is dropping significant flow once it touches 5bar of pressure and not to mention walbros as well.... so for a 7 bar the injectors will damage and there will be no flow at all. regulators like sard can support up to 800kpa only....above that, u you will no fuel return or no flow.

but joeker one more thing to remind. the fuel pressure does increase proportionally wid your manifold on sard and oem regulators. 1bar boost will equal to base pressure + your 1 bar. only on rising rate it will not be proportional.

and we are really off topic by alot.... im asking whether base pressure is whether set on:-
during car idle with vacuum unplugged
OR
during car idle with vacuum plugged. thanks.

**my logic tells me its set wid vacuum unplugged. but if anyone says this is not the way then maybe you could explain why not and the reason. lets pls not divert anywhere else

     

cyborgsabah

always set your base fuel pressure with the vac line unplugged... why? because the vac at idle is vary from one engine to another, even with the same type of engine due to cams upgrade, idle rpm, etc.. etc..

     

FatAssRubber

cyborg..... hmmmm .... correct answer.. wrong explaination.... not really wrong.. just half right.. half "foreman" answer..


:)

     

cyborgsabah

care to explain which half of my explaination is wrong.. i also want to know...

     

ondgennis

yaya...i want to know also..after go through this topic i also become confuse already...

conclusion pls...