Aftermarket fuel pressure regulators

[Slavvy 0]

My question is simple. Can someone please explain to me how these things actually function? As in the mechanical workings of them, and their purpose in general.

My understanding is that the pressure regulator controls how much fuel bleeds off from the end of the rail and back to the pump. Because a factory one depends on vacuum, it closes at WOT throttle and then you are theoretically running at the maximum pressure the fuel pump is capable of. If this is the case, what is the point of an aftermarket regulator? Unless I'm understanding this completely wrong, it has no ability to increase your fuel pressure beyond the amount a factory one is capable of maintaining. So if you wanted more fuel it seems like a more powerful pump/bigger injectors would make much more sense.

Can anyone enlighten me?

[e30ftw 410]

An adjustable one you can raise or lower the maximum fuel pressure.

[*Glenn* 854]

A BMW fuel pump is capable of pressures higher than that needed by the engine and has a high flow rate. The regulator bleeds off fuel with and without vacuum dependant on the engines needs. At idle (full vacuum), the pressure is maintaned at 2.5 bar and bleeds off fuel back to the tank. At WOT (no vacuum) the pressure is controlled (increased) to 3 bar to give enrichment under load and still bleeds off fuel. The DME controls injector duration to deliver the correct fuel requirements dependant on temperature, TPS position, RPM, air flow and load from their specific sensors on the engine (DME input signals)

Aftermarket regulators are used to aid fuel pressure regulation for tuning purposes dependant on setup and you can raise & lower fuel pressure, some can regulate both pressures, with vacuum & without vacuum. Quite often used for Turbos & SC set ups.

Using larger injectors that deliver more fuel and controlling duration in most cases is far better and cannot normally be controlled by a standard DME (all dependant on engine modifications). Thats why an aftermarket ECU is needed such as Link, so that duration can be set at any given point to supply the correct amount of fuel along with ignition control and engine sensor inputs. There is alot more to this, I just don't have time to write a book though. Hope this helps the OP.

Edited December 15, 2009 by *Glenn*

[CamB 48]

And for when you have forced induction, under boost the regulator allows increased fuel pressure to match the boost.

The standard regulator is fine in almost all cases. You would use:

- an adjustable one (or a higher rated one) where you wanted to change the fuel pressure (eg, keep the same injectors after making adjustments to the engine which increase the fuel requirement in a way that the computer can't account for). People often use them in conjunction with an aftermarket chip or computer so that they don't have to buy new injectors; or

- a rising rate fuel pressure regulator, when you want to try and run forced induction without changing the ECU. The rising rate means it increased the pressure faster than the boost increases.

[No name user 379]

every efi car has a rising rate regulator

even a non turbo reg will work buy adding extra pressure as its still receives a boost/vacum single on top to raise fuel flow.

the down side of aftermarket regs is they are often used for the wrong reasons and the wrong way.

meaning you add a higher flow pump and the fuel pressures goes up so you add a aftermarket reg to turn the pressure down,this is OK to a certain point but its the return seat size in the reg thats a problem.

each reg is made to match a certain fuel flow based on seat size,this is the hole the fuel flows thru to control pressure based on volume.

regs come in sizes from .100 to .150 depends on ltrs/min, the biggest mistake that's made is when bigger injectors are fitted then fit another reg to get them to run at idle,bad move!!!

ive seen pressure being dropped down as low a 20psi to allow it to run,now you have a very poor spray pattern which does nothing for performance.

as mentioned above a re-flash of the ecu or aftermarket is the way to go,so you don't really need a aftermarket reg.

im a big fan of getting away with a high a pressure as possible but never go over 85psi rail pressure or the it ll blow the needles of the seat and you have no control over them.

[CamB 48]

every efi car has a rising rate regulator

Yes, I probably wasn't clear. I mean the fuel regulators you can buy which increase the fuel pressure faster than the boost pressure. It seems the proper name is FMU, eg:

http://www.superchargersonline.com/product...=fuelsystem_fmu

Either way, my personal view for the original poster is ... don't use them and do it properly.

Edited December 17, 2009 by CamB

[No name user 379]

Yes, I probably wasn't clear. I mean the fuel regulators you can buy which increase the fuel pressure faster than the boost pressure. It seems the proper name is FMU, eg:

http://www.superchargersonline.com/product...=fuelsystem_fmu

Either way, my personal view for the original poster is ... don't use them and do it properly.

i agree totally the yanks use those things where ever they can,called being lazy

[*Glenn* 854]

i agree totally the yanks use those things where ever they can,called being lazy

Probably more that fact that its a lack of knowledge on how to do things properly... makes me laugh how alot of the younger ones on here and other forums think that if the yanks do something, it must be cool and the correct way to do things... yeah right

[tibbs.james 1]

Not that i really know anything or have much experience

But in the 300zx turbo scene that I am a part of it seems that an aftermarket fuel Reg Is often used with an aftermarket pump & injectors along with an ECU setup to control it all.

On the Early style 300zx turbos like the one I own, people often install an aftermarket Fuel Press Regulator along with a high flow in tank pump to get the most out of their stock injectors and turbo. I'e to raise the base fuel pressure when so that when injectors are getting maxed out they can extract a bit more flow out of the injectors.

I am not saying this is a good or bad thing only that it is an example I personally know of and for right or wrong it seems to work for the person.

[Slavvy 0]

Probably more that fact that its a lack of knowledge on how to do things properly... makes me laugh how alot of the younger ones on here and other forums think that if the yanks do something, it must be cool and the correct way to do things... yeah right

Hope I'm not one of them youngin's

My initial view was that if you had appropriately sized injectors and a reflashed/aftermarket ECU you wouldn't have to worry about fiddling with the fuel pressure the hard way, but I wanted to hear people more knowledgeable than me explain things. Thanks.

Another question I have is whether all bosch injectors of the same shape are interchangeable. As an example, m30 injectors seem to be externally identical to falcon straight six injectors (and, as seen in another thread, mustang v8 injectors). The only difference seems to be cc rating. Obviously this means that they'd plug into the loom and connect to the rail correctly, but is there any difference in impedence which could affect the behaviour of the factory ecu? I'm meaning the electrical side of things, not the effect a lesser/greater amount of fuel would have on the engine as a whole.

What a mouthful haha

[No name user 379]

Hope I'm not one of them youngin's

My initial view was that if you had appropriately sized injectors and a reflashed/aftermarket ECU you wouldn't have to worry about fiddling with the fuel pressure the hard way, but I wanted to hear people more knowledgeable than me explain things. Thanks.

Another question I have is whether all bosch injectors of the same shape are interchangeable. As an example, m30 injectors seem to be externally identical to falcon straight six injectors (and, as seen in another thread, mustang v8 injectors). The only difference seems to be cc rating. Obviously this means that they'd plug into the loom and connect to the rail correctly, but is there any difference in impedence which could affect the behaviour of the factory ecu? I'm meaning the electrical side of things, not the effect a lesser/greater amount of fuel would have on the engine as a whole.

What a mouthful haha

if there a Bosch style then they should fit but the impedance is most important or the ecu injector drivers can blow,there's also peak hold and saturated injectors but that's another thing again

[Slavvy 0]

if there a Bosch style then they should fit but the impedance is most important or the ecu injector drivers can blow,there's also peak hold and saturated injectors but that's another thing again

I've just tested the resistance across a motronic m30 injector, an early model SOHC falcon injector, and a late model falcon one. The first two are identical in shape (but different in part number, the little nozzle isnt the same), and they both have about 39 Ohms. The later style injector, which has the same dimensions (ie same tip diameter, same height, same plug for the fuel rail etc) but different shape, was considerably less at around 29 Ohms.