Can Anyone Tell Me How A Fuel Pressure Regulator Works?

[M3Evo 0]

Can anyone tell me exactly how these things work, with particular regard to the vacuum signal line that goes into them?

 

Also, is it inadvisable to connect the vacuum line to only one throttle on a set of TBs?

 

Only ask as I've just disconnected the line on my car and whereas this morning it wouldn't rav above 2000rpm, it's now happy enough doing whatever

 

Cheers!

 

Alex

[DrSeuss 0]

fuel pump supplies fuel at 3.3 bar fpr regulates that to 3 bar above inlet depression. Its a diaphragm controlled valve that either sends fuel to the tank or into the fuel rail. Its quite common to disconnect it, in fact all of the people i can think of running tb's have. On a forced induction engine its not recommended though!

[PumaRacing 1]

Can anyone tell me exactly how these things work, with particular regard to the vacuum signal line that goes into them?

 

In its simplest form a sprung loaded diaphragm with fuel pressure on one side and atmospheric on the other. The diaphragm opens a bleed back to the fuel tank at a preset pressure so that only this pressure is transmitted to the injectors. However a more sophisticated form is needed to cope with turbocharged cars and can equally be applied to N/A ones if desired.

 

Imagine a turbocharged car with very high boost pressure, say 45 psi, and a diaphragm set to deliver fuel at 45 psi. At full boost the air pressure in the inlet manifold would be be the same as in the fuel lines and no fuel would come out of the injectors. At lower levels of boost the net fuel pressure would be above zero but still lower than desired. What is needed is a constant pressure over and above that in the manifold so a line from the manifold is taken to the 'atmospheric' side of the diaphragm to deliver a counter pressure to the fuel pump.

 

In a normally aspirated car the manifold pressure varies between just under atmospheric at full throttle and close to zero on a trailing throttle at high rpm but is always less than atmospheric. Connecting the diaphragm to the manifold therefore always reduces the net fuel delivery pressure. By removing yours you have increased the fuel pressure and richened the mixture - a bit at full throttle and a lot at part throttle. That should tell you something about how the mixture was wrong to start with if the car now runs better.

 

Also, is it inadvisable to connect the vacuum line to only one throttle on a set of TBs?

 

It's better to connect at least a couple of runners, and preferably all four, to obtain a steadier signal. Heavy pulsations occur in each runner of a single butterfly per cylinder system which isn't good for fuel diaphragms or brake servo systems.

 

Only ask as I've just disconnected the line on my car and whereas this morning it wouldn't rav above 2000rpm, it's now happy enough doing whatever

 

Cheers!

 

Alex

[M3Evo 0]

A haa, many thanks for the replies guys.

 

Wonder how weak the mixture was!

 

Think I need to do some mods to my TBs so that they're all linked by a common chamber. Wonder if something like an old fuel rail would work.

 

Anyway, hopefully it'll run a bit better when it goes into the garage for the welding and things tomorrow!

[TT205 42]

Did you find a way of linking each TB?

[M3Evo 0]

Not even looked into it yet!

 

Why you askeeee?

[TT205 42]

Asking as I'm not sure mine is connected to a vacuum line at all - will have to check

 

Dave

[M3Evo 0]

A-haa. By the sounds of it, it shouldn't make any odds as long as it was mapped like that?

 

To link each TB it's gonna be a case of making up little tails that can be fitted to each bore which means taking the whole lot apart, drilling and tapping some holes, installing the tails and then grinding them smooth inside the bores again.

 

A long and boring process!