Roojai

Does the fuel pressure regulator keep the pressure to a set level, if so what level is it.

Does it adjust the level dependant on the conditions or just keep it at them same place.

If you fit a walboro pump will the fuel pressure increase before AND after the standard regulator?

If the fuel pressure is increased after the regulator, does this mean that the injectors are pumping more fuel into the engine.

Answers to any and all of the above please

Jolly Green Monster

iTrader: (4)

set pressure + manifold pressure.. standard fuel pressure reg is 2.8~3bar depending on year. After market adjustable regulator will keep pressure at what you set it to plus manifold pressure (boost).

only increased / decreased via manifold pressure increasing / decreasing

pressure at the fuel rail / injectors should remain unchanged.. more fuel should be flowed back to the tank.. some original fuel pressure regs get over powered at low fuel usage like on idle or cruise and the pressure does increase in the fuel rail but this doesn't seem consistent, in that it might be fine on one car and not on another.

fuel is supplied to the fuel rail / injectors and then flows to the regulator which regulates the pressure in the fuel rail and flows varying amounts of fuel back to the fuel tank to maintain the correct pressure.
If the pressure is increased by the pump change before the regulator therefore in the fuel rail then yes more fuel will be injected in to the engine.

Simon

crispyduck

iTrader: (1)

I asked similar questions a while back and all made sense after Pedroskate sent me this:

Pedroskate wrote:
"Now this is all a personal theory that only works if the Walbro pump does not have an internal relief or regulate presure internally in any way. So with that assumption, I would argue that as the the fuel presure regulator (diaphragm presure controller) only senses inlet manifold presure, it a matter of boost presure on one side of a diagphragm and fuel presure on the other. If the base line fuel presure from the pump is higher (allbeit slightly) than that of the standard pump, then the point of equilibrium between the two sides of the diaphragm will alter. Consequently the fuel presure is proportionally higher throughout the range; in my case between 4 and 6 psi. The car ran 14.236 quarters at Santa Pod last time out, I'm convinced it's now in the 13s just by changing the pump.
Regards
Pete"

Hope this helps,
-Steve.
P.S: That reminds me I think I had better add that to my knowledge base.

Delboy2

No - The fuel pressure is set at ~3 bar (43.5psig) at atmospheric pressure (vac/pressure pipe from FPR to manifold disconnected) - The fuel pressure regulator is a 1:1 rising rate which means the fuel pressure rises and falls inline with the inlet manifold pressure for example :- if the fuel pressure is 43.5psig(3bar) at atmospheric, when you reconnect the vac/pressure pipe back to the FPR & back to the manifold when the engine is running the manifold pressure will be in vacuum at around -10psig (-0.69bar) so the fuel pressure will fall to 33.5psig. When driving and the manifold pressure rises to 15psig (1.03bar) the fuel pressure will also rise to 58.5psig (4.03bar)

The fuel pressure may rise but this will be dependant on whether the std FPR can cope with the increased pressure/flow AFAIK on the early classics the FPR's find it difficult to cope with an uprated pump whereas the later models seem to be fine


In a word yes as the duration in which the injector is open will stay the same but with the increase in pressure/flow will result in more fuel passing through the injector will increase for the same opening time.

Cheers

Roojai

Thanks to all three of you for good clear responses