FPR

[Jesh]

okay so i suck at this search engine and cant find very much about fuel pressure regulators. i know how they work. but how does a adjustable one work? i know fuel pressure stock is 43psi, how much should i turn it up on a mildly modified VR4 (big 16g, exhaust, intake, mbc) but back to how does a adjustable fuel pressure regulator work. can someone spell it out for me.

 

[mooserage]

As for the search engine: Don't forget to use + symbols in front of all terms i.e.: +fuel +pressure +regulator .

Basically you only need an adjustable fuel pressure regulator if you have an upgraded fuel pump. This is because your higher flowing fuel pump will do exactly that, flow more fuel than a stock unit consistently. This is a problem because it means that your stock regulator is now seeing more flow and thus your fuel pressure increases in the system because it was designed to flow a set amount of fuel (stock amount). This is an issue because higher pressure means more fuel is forced into your injectors with each pulse resulting in your car adding more fuel than before, therefore you have a rich condition. This is not ideal as it is detrimental to making power and burning fuel efficiently.

An adjustable regulator allows you to adjust your fuel pressure up or down, and therefore when you have that high flow pump putting out 50psi, you can adjust it down to the stock 43psi. So, now you have the proper amount of pressure, and because you have a higher flowing fuel pump you can turn up the boost and your fuel pump won't peak flow as quickly.

Where does this leave you. If you have an upgraded pump, you want to reset your fuel pressure with your regulator to the stock setting. If you are just adding an AFPR to a stock pump, well there isn't much point. You can add a little pressure to allow for a richer condition if you are worried the car runs lean, but honestly its better to get another form of tuning for that (i.e. SAFC, Keydiver Chip, DSMLink, etc.). With that 16G you are limited by a stock pump at some point because eventually as you turn the boost up you will find that the stock pump cannot flow enough fuel and will starve the engine of fuel, creating a lean condition, which is very bad.

So basically, get an AFPR if you have an upgraded pump, or get one. Otherwise don't worry about it and make sure you don't turn the boost up too much for your setup.

Lastly, to properly set the fuel pressure you need to get the car to idle warm (steady idle), remove the vacuum hose that goes to the regulator, and adjust it to 37psi, this is the base idle fuel pressure.
-shamus

If I missed anything I'm sorry, but someone will correct me /ubbthreads/images/graemlins/smile.gif

 

[Jesh]

thanks that exactly what i wanted to know!

 

[CarRacer]

He basically got it correct except for the reason the car runs rich.

The reason the stock regulator causes a rich condition with an upgraded pump is due to the return circuit size. The regulator sends any fuel that the engine doesn't use back to the tank, and the return line hole is extremely small. The upgraded pumps send too much fuel and overflow the return hole and the fuel ends up going into the engine. When you start getting into boost or full throttle situations, the FPR doesn't need to return as much fuel so it starts running better.

If you want to control the fuel curve over all throttle positions buy an adjustable FPR.

 

[Muskrat]

Also, stock base fuel pressure is 37.5 psi, not 43 psi.

 

Speaking of adjustable FPR's. What's a good one to put on our cars? I'm in the market for one. Another question is, will it be pointless to do with a rewired pump, or should I just upgrade that too in the process?

Sorry about the thread Jack.

 

Quoting Muskrat:
Also, stock base fuel pressure is 37.5 psi, not 43 psi.



To be exact, its 36.3psi, but we generally round it up to 37psi.

Quote:
Speaking of adjustable FPR's. What's a good one to put on our cars? I'm in the market for one.



You usually want to stick to a good name brand, like Aeromotive or Fuellab, although I have had good luck with a generic that I have sold in past. In general, if it has -6 AN fittings, you should be good to go. If it is a cheap eBay AFPR with barb type fittings, its best to pass on that one. Just make sure its a 1:1 AFPR made for fuel injected applications, not carb.

Quote:
Another question is, will it be pointless to do with a rewired pump, or should I just upgrade that too in the process?



Rewiring usually isn't enough to overrun the stock FPR, so an AFPR is not needed. You *could* use it to raise the base fuel pressure, to stretch the injectors a bit, but that is counterproductive with a stock pump. The fuel volume out of a fuelpump drops greatly with increased pressure, so raising the base fuel pressure on a stock pump usually just means you will now run out of fuel volume from the fuelpump before you run out of injector.

 

Thanks Jeff. I'll soon be getting ahold of you for ECU upgrading. I hope the previous offer still stands. /ubbthreads/images/graemlins/grin.gif

 

[solidviper89]

Quoting Jesh:
okay so i suck at this search engine and cant find very much about fuel pressure regulators. i know how they work. but how does a adjustable one work? i know fuel pressure stock is 43psi, how much should i turn it up on a mildly modified VR4 (big 16g, exhaust, intake, mbc) but back to how does a adjustable fuel pressure regulator work. can someone spell it out for me.



Stock pressure for a galant is not 43psi its approximately 37 with hose off, 43psi is for a 2g IIRC.

Anyways, the regulator that you want is an Adjustable FPR, not a rising rate one. With an AFPR, your pressure at idle can be adjusted and set to a different level. The AFPR increases fuel pressure at a 1:1 ratio with boost, in other words, at 26psi of boost the regulator will increase fuel pressure by 26psi.

 

I'm pretty the turbo A/T cars with the 390cc injectors have a 43 psi fpr.

 

[Chad989of2000]

Quoting keydiver:


You usually want to stick to a good name brand, like Aeromotive or Fuellab



+1 Aeromotive works very well and makes for hassle free adjustment.

 

[1qkfwd]

The autos are 43 also.

Another small thing to remember is even if you stick with the factory fpr it doesnt always have a 1:1 ratio. I was playing around with different regulators in a sleeper car that I built and some of the regulators would only go 10-15 over base pressure, even after sealing the fpr. Thats with a mechanical gauge ran in the cab. If your stuck on minor mods and a 190LPH or smaller pump you will be just fine on the stock fpr. Most of them leak around the hat but nothing silicone can't fix.