Fuel Pressure Regulators
Discussion
Please could someone explain Fuel Pressure regulators.
As I understand it on the standard system fuel is supplied from the pump to the fuel rail which feeds all the injectors. The Fuel rail then feeds into a pressure regulator which bleeds fuel back to the tank at a rate that correctly controls the rail pressure. The regulator maintains the pressure relative to the plenum pressure rather than atmosphere so there are three pipes connected, plenum pressure, fuel rail and return to tank. For this to work the pump must be capable of supplying more fuel than required.
OK so far…
However what happens if you don’t have a plenum. Can the standard regulator be used referenced to atmosphere or is a different sort of unit normally used ? Most of the adjustable ones I can see in the catalogues seem to have just two pipes. Presumably they are still attached at the return end of the rail but reference against a spring.
As I understand it on the standard system fuel is supplied from the pump to the fuel rail which feeds all the injectors. The Fuel rail then feeds into a pressure regulator which bleeds fuel back to the tank at a rate that correctly controls the rail pressure. The regulator maintains the pressure relative to the plenum pressure rather than atmosphere so there are three pipes connected, plenum pressure, fuel rail and return to tank. For this to work the pump must be capable of supplying more fuel than required.
OK so far…
However what happens if you don’t have a plenum. Can the standard regulator be used referenced to atmosphere or is a different sort of unit normally used ? Most of the adjustable ones I can see in the catalogues seem to have just two pipes. Presumably they are still attached at the return end of the rail but reference against a spring.
If the injectors are after the throttle plate and are subject to engine vacuum, then plumb the FPR pipe into the same area. If you are running throttle bodies you can run a pipe to each one and tee them together.
The whole idea is that there is a constant pressure differential maintained between the injector and the inlet port.
You can "map" around it as well and just have a static fuel pressure. But the idea is that if you are running bigish injectors, with the lower fuel pressure at idle its easier to tune the idle area.
hth.
The whole idea is that there is a constant pressure differential maintained between the injector and the inlet port.
You can "map" around it as well and just have a static fuel pressure. But the idea is that if you are running bigish injectors, with the lower fuel pressure at idle its easier to tune the idle area.
hth.
Eliot,
A question for you if I may interject.
I'm about to fit Megasquirt 2 to my 4.2 injected RV8.
Would you suggest a fixed 3.9 Bar reg or the 0-5 Bar variable unit listed here:
http://www.webcon.co.uk/Downloads/WFR1.pdf
Is there ever any need to have a lower or higher fixed pressure in this particular engine such as for state of tune, injector type etc?
Thanks.
Phil
420 SEAC
A question for you if I may interject.
I'm about to fit Megasquirt 2 to my 4.2 injected RV8.
Would you suggest a fixed 3.9 Bar reg or the 0-5 Bar variable unit listed here:
http://www.webcon.co.uk/Downloads/WFR1.pdf
Is there ever any need to have a lower or higher fixed pressure in this particular engine such as for state of tune, injector type etc?
Thanks.
Phil
420 SEAC
Transmitter Man said:
Eliot,
A question for you if I may interject.
I'm about to fit Megasquirt 2 to my 4.2 injected RV8.
Would you suggest a fixed 3.9 Bar reg or the 0-5 Bar variable unit listed here:
http://www.webcon.co.uk/Downloads/WFR1.pdf
Is there ever any need to have a lower or higher fixed pressure in this particular engine such as for state of tune, injector type etc?
Thanks.
Phil
420 SEAC
What injectors are you using?A question for you if I may interject.
I'm about to fit Megasquirt 2 to my 4.2 injected RV8.
Would you suggest a fixed 3.9 Bar reg or the 0-5 Bar variable unit listed here:
http://www.webcon.co.uk/Downloads/WFR1.pdf
Is there ever any need to have a lower or higher fixed pressure in this particular engine such as for state of tune, injector type etc?
Thanks.
Phil
420 SEAC
Essentially the injectors will have a defined flow rate a a specific pressure which is typically 3 or 3.5 bar.
Benefit of an adjustable regulator is that you can effectively adjust the size of the injectors if they are a bit too big or too small for your engine.
eliot said:
What injectors are you using?
Essentially the injectors will have a defined flow rate a a specific pressure which is typically 3 or 3.5 bar.
Benefit of an adjustable regulator is that you can effectively adjust the size of the injectors if they are a bit too big or too small for your engine.
Thats total rubbish ! The injectors have a recommended min and max pressure ,mine are 2.5 to 3.5bar ,the whole range will give a good spray pattern .Essentially the injectors will have a defined flow rate a a specific pressure which is typically 3 or 3.5 bar.
Benefit of an adjustable regulator is that you can effectively adjust the size of the injectors if they are a bit too big or too small for your engine.
The fueling is controlled via the ECU by changing the VE values.
People try and tweak the fuel presure on the cux because you can`t change the values. It`s a bit of a bodge .
Edited by SILICONEKID350HP on Tuesday 12th February 23:13
SILICONEKID350HP said:
Thats total rubbish !
No it's not - the question was in relation to Megasquirt.SILICONEKID350HP said:
The injectors have a recommended min and max pressure, mine are 2.5 to 3.5bar ,the whole range will give a good spray pattern .
And it’s the fact that an injector can work within a certain range is what I'm referring to. For example an injector rated at 24Lbs @ 43 psi(3 bar) could be run at 60psi(4bar) and it would flow the same as a 29lb injector. Of course there are downsides to this; increased fuel pump wear (and current consumption), more stress on your pipework and of course more work for the injectors to open and close against that increased pressure. So it’s not a replacement for correctly sized injectors.But the point I was trying to make is that you can adjust the flow [apparent size] of the injector rather than being locked to a specific flow rate that a non-adjustable FPR would do.
An example of this is with megasquirt - in order to attain a desirable idle pulsewidth you have to select between two or four squirts per cycle and alternating/simultaneous injecting. With a particular sized injector, you could find yourself on the border of two different schemes and face having a very small or long idle pulsewidth. With an adjustable regulator, you can adjust the flow rate of the injector which results in a different baseline idle pulsewidth.
When adjusting fuel pressures, one must not forget that the static baseline pressure reduces with engine vacuum and of course also increases if (like me) you have forced induction. So that injector that you ramped up to 60psi will actually be running at 70psi with 10lbs of boost.
SILICONEKID350HP said:
The fueling is controlled via the ECU by changing the VE values.
I think you will find I’m very familiar with how an ECU works.SILICONEKID350HP said:
People try and tweak the fuel pressure on the cux because you can`t change the values. It`s a bit of a bodge .
The question was related to Megasquirt – not 14cux. Tweaking the static fuel pressure on something like the 14CUX is indeed not a good idea, as it would alter the entire fuelling.
And fitting a rising rate fuel pressure regulator (which you may be getting confused with) is even more of a bodge and is typically used where someone wants to avoid (or cant) map the ECU. But as I said, the question was related to Megasquirt.
eliot said:
The question was related to Megasquirt – not 14cux.
Tweaking the static fuel pressure on something like the 14CUX is indeed not a good idea, as it would alter the entire fuelling.
And fitting a rising rate fuel pressure regulator (which you may be getting confused with) is even more of a bodge and is typically used where someone wants to avoid (or cant) map the ECU. But as I said, the question was related to Megasquirt.
So pedantic Tweaking the static fuel pressure on something like the 14CUX is indeed not a good idea, as it would alter the entire fuelling.
And fitting a rising rate fuel pressure regulator (which you may be getting confused with) is even more of a bodge and is typically used where someone wants to avoid (or cant) map the ECU. But as I said, the question was related to Megasquirt.
SILICONEKID350HP said:
I thought you were talking about the clock work 14cux ..I want to set mine at 40psi ,how much is involved to change the settings on the ECU to suit the pressure.
If i changed it to 40 psi would the whole map be wrong .
why would you want to do that? it will affect the spray pattern and increase the amount of fuel injected throughout the rev range requiring a remap. if your fueling is running lean at the top cos your injectors are to small...replace them.If i changed it to 40 psi would the whole map be wrong .
If you are running lean at the top check check your fuel rail pressure at the top end if its dropping it could be weak fuel pump or restricted fuel filter at fault. They were in my case when i initially ran redtops, i had to replace the pump with a Bosch 044 and larger fuel filter.
db418BHP said:
Just to add to the mix.
I run a Weber Alpha fixed rate and the vaccuum is not connected.
Its fed by a Bosch 044 and fuelling is controlled by MS2.
On the standard Bosch greens (cleaned and matched) i have 275 @ wheels and can easily achieve 29 mpg.
Can you send me your MSq cheersI run a Weber Alpha fixed rate and the vaccuum is not connected.
Its fed by a Bosch 044 and fuelling is controlled by MS2.
On the standard Bosch greens (cleaned and matched) i have 275 @ wheels and can easily achieve 29 mpg.
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