Fitting Fuel Pressure Regulator - Help

[Ste]

Anyone know the standard fuel pressure?.

Also anyone know how to fit a fuel pressure regulator on a VTS engine?.

Im assuming i just pull the inlet off and its somewhere around the fuel rail and injectors?....

[gd16]

Standard VTR - 3.5bar, found under rear bench, under one of the circular plastic covers
Standard VTS - 3 bar, on the end of the fuel rail (AFAIK)

[williamsvts]

yeah, its just next to throttle body. just need to remove airbox and you can get to it.

[Ste]

Got the bugger cheers!

[Ste]

Ok so i have my FPR, it has a total of 3 holes. One Fuel Inlet, One fuel outlet and a smaller hole that i believe is the vacuum.

Now all i need to know, which is pipe from the fuel pump, which is the fuel return and which is the vacuum hose;










I think ive labelled them up wrong, i think that A.2 is the vacuum, B.1 is the fuel inlet and B.2 is the return. Yes/No.

[Ste]

And one last thing, the flow of the injectors is controlled by the pressure but the ammount of fuel allowed to enter is controlled by the pulse width.

So if the pressure is slightly higher and pulse width is short then it would fuel less than if the pressure was normal and pulse width was very long.

Yes / No ?

[gd16]

A1, B3 - Correct

A2 - Vacuum (from inlet)
B1 - Fuel in (from pump)
B2 - Fuel return (to tank)

[gd16]

Originally Posted by Ste

And one last thing, the flow of the injectors is controlled by the pressure but the ammount of fuel allowed to enter is controlled by the pulse width.

So if the pressure is slightly higher and pulse width is short then it would fuel less than if the pressure was normal and pulse width was very long.

Yes / No ?

Not entirely understanding what you're saying/asking. But hopefully this will help;


Standard pulsewidth, standard pressure = fine.

If fuel pressure drops off, pulsewidth needs increased do insure the same amount of fuel is put into the engine.
Likewise, if you swap for a larger FPR so fuel pressure is increased, pulse width will decrease.



You've then got things like pressure referenced FPR. For example, on low throttle the engine will be sucking in air at 7psi (0.5 bar). Say your using a 3.5bar FPR that isn't referenced to the inlet pressure - fuel will be getting pushed out of the injectors at 3.5bar, and getting sucked out at 0.5bar. So 4bar total.

Now the same setup, but the FPR now has a hose referencing it to the inlet pressure. Because the inlet pressure is 0.5bar, the FPR is only pushing the fuel through the injectors at 3bar. But again because of the vacuum pulling the fuel through the injectors it is really 3.5bar total.


Referenced FPR's (as per standard) should always read the same FPR no matter what the inlet pressure. Non-referenced will vary depending on inlet pressure.

Then on top of that still, i think you get referenced constant ones (ie for every 1 psi inlet pressure it doubles the FPR pressure)

[Ste]

What do i do with the standard FPR, blank of the vacuum and leave it or remove it and blank off that end of the fuel rail?.

[williamsvts]

what fpr are you trying to fit? if its an fse i wouldnt bother as they are rising rate. the fuel pressure increases as the revs do. i would use a fpr that fits the standard fittings. 3bar from a vts, 3.5bar from a vtr and some VAG engines have a 4bar that fits teh vts. found 1 on a merc yesterday at the scrapyard that would fit but didnt have the pressure marked on it any where.

[Ste]

Its an uprated one, im fitting a megasquirt which will control the lot so im not noobing it and just overfueling and im going supercharged so im fitting all the bits i need so when i make the megasquirt loom the engine bay looks lush and tidy.

[williamsvts]

so why are you wanting to use a non standard fit fpr? i dont see the point?

[Ste]

Whats point in that post?.

I want more fuel pressure. Cant see 350bhp without upping it.

[gd16]

Ste, think you'll need to expand on that.

If you said ' Can't see 350bhp on the injectors i've got without upping it ' then i'd possibly agree.

However you'll be able to see 350bhp fine on 3bar fuel pressure, as long as you spec the injectors/internal fuel line diameter/fuel pump fine.


With slight exceptions, there's no real need to change from 3bar FPR to 3.5FPR just because you're going for boost. As long as the injectors are specced properly for the power and FPR you shouldn't have an issue.

If you speak to John @ GMC, or Matt @ QEP and ask what injectors they would recommend for 350bhp, using x bar FPR they will let you know whats available. I doubt either will advise you to change the FPR to a higher one, unless they've got a set of injectors that'll almost be enough at 3 bar, but would definately manage the flow rate at 3.5bar.

[williamsvts]

you can get various sizes what are a straight swap with standard i mean.

[Ste]

You get better fuel atomization from running a higher bar, which is why i want to fit the fpr. Necessity isnt why im doing it.

That gives better driveability, better everything.

[williamsvts]

i know that. but what im saying is you can get various fuel pressures in a standard fit fpr. you dont need to go aftermarket to get a higher or lower fpr. i would just use a vtr fpr which is 3.5bar, what i have on mine, you can get a 4bar from some mk4/5 golfs which are a straight swap and GMC sell even higher pressures, or they did sell them. not sure if they still do.

[Ste]

Originally Posted by williamsvts

i know that. but what im saying is you can get various fuel pressures in a standard fit fpr. you dont need to go aftermarket to get a higher or lower fpr. i would just use a vtr fpr which is 3.5bar, what i have on mine, you can get a 4bar from some mk4/5 golfs which are a straight swap and GMC sell even higher pressures, or they did sell them. not sure if they still do.

Aah i see, sorry i totaly misunderstood.

[boz]

as above mate, you can get a higher pressure fpr that will just swap in place of your oem one. no need to mess about fitting an aftermarket one.

its all about getting the injectors specced up right with your fuel pressure.