Fuel pressure

[mike 850]

Maybe an obvious one but I hooked up a gauge to the fuel rail and on idle i have just over 1 bar fuel pressure, have swapped out the regulator for another and its still the same, I think it should be 3 bar above manifold pressure? so should be over 2 bar on idle?

does this mean the pump is tired? fuel filter was done just over 1000 miles ago

Cheers

[mike 850]

Anyone have any ideas? could someone please measure there fuel pressure on idle to see if its normal?

[merc85]

Anyone have any ideas? could someone please measure there fuel pressure on idle to see if its normal?

Hi mike, what makes you think you have low fuel pressure?

[Dangerous Dave]

Sounds like you have a problem somewhere.

Like you say the pressure should be 3bar plus manifold pressure or vacuum. This is so the injector 'sees' 3 bar all the time, otherwise incorrect amounts of fuel would be injected by the ecu as the fuel constant is fixed in the ecu memory.

So at idle the mainfold is under vacuum (approx 0.6bar) so the fuel pressure at the injector should be 2.4 bar.
Under boost (say 1bar) the fuel pressure at the injector is increased to 4bar to counteract the pressure in the manifold.

Like you say could be a dodgy pump or possibly a leaking inejctor or something else. Is it running rough or has the MPG dropped?

Hope this makes sense. Obviously I could be talking balls, I have not done any actual tests on my engine to prove this.

[oblark]

Sounds like you have a problem somewhere.

Like you say the pressure should be 3bar plus manifold pressure or vacuum. This is so the injector 'sees' 3 bar all the time, otherwise incorrect amounts of fuel would be injected by the ecu as the fuel constant is fixed in the ecu memory.

So at idle the mainfold is under vacuum (approx 0.6bar) so the fuel pressure at the injector should be 2.4 bar.
Under boost (say 1bar) the fuel pressure at the injector is increased to 4bar to counteract the pressure in the manifold.

Like you say could be a dodgy pump or possibly a leaking inejctor or something else. Is it running rough or has the MPG dropped?

Hope this makes sense. Obviously I could be talking balls, I have not done any actual tests on my engine to prove this.

Not the old fuel constant :)

[mike 850]

The injectors were refurbed less than 1k ago, the reason I think there was an issue is the it leans out under boost, goes to 13's. measured the pressure on the fuel rail as im running blues and want to get them running at 3.8bar so have got an adjustable FPR, thought id measure before i changed the fpr

[no1tosh]

im sure i have low fuel preasure or i think i do.

now ive been told that with the car at idle if i put my gauge on the end of the rail it should read 3 BAR or 43 PSI
is this correct?
as mine measures between 32 and 35 psi at idle then if i give it a rev it goes up to 40 psi, surly this isn't right?

i understand that for every bar of turbo preasure you add then it goes up a bar with fuel.

[merc85]

Fuel pressure should be 43.5psi

see here, http://www.volvoclub.org.uk/tech/service/850/BasicTesting-Turbo.pdf

[no1tosh]

ya that where i got it from, ive downloaded as many of those guides as i can find for keep safes:)

cheers mate, i had just read a few conflicting things when google searching so getting slightly confused:redface:

[Dangerous Dave]

The injectors were refurbed less than 1k ago, the reason I think there was an issue is the it leans out under boost, goes to 13's. measured the pressure on the fuel rail as im running blues and want to get them running at 3.8bar so have got an adjustable FPR, thought id measure before i changed the fpr
Is the gauge you're using calibrated correctly? (considering you've tried another FPR)


im sure i have low fuel preasure or i think i do.

now ive been told that with the car at idle if i put my gauge on the end of the rail it should read 3 BAR or 43 PSI
is this correct?
as mine measures between 32 and 35 psi at idle then if i give it a rev it goes up to 40 psi, surly this isn't right?

i understand that for every bar of turbo preasure you add then it goes up a bar with fuel.
Sounds right to me bud...
34psi (2.4bar ish) is about right at idle which is the 43.5psi (3bar) less the manifold vacuum which is usually around 9psi (0.6bar ish)
When you rev the engine the vacuum will decrease which means the fuel pressure is increased by the FPR

[no1tosh]

im confused

[960kg]

The standard fuel running pressure is between 30.45 and 55psi.

When started the engine should immediately go to 45psi.

The most important thing is the residual pressure!........it should hold 2bar or 29psi for at least 20mins if it doesn`t then the injectors may be leaking or the valve in the fuel pump has gone kaput.

[no1tosh]

right well when i start the car it gets 32-35 psi.

sorry to be a pain i just couldnt understand weather when i have the gauge on the end of the rail weather it should be 43psi or 35 psi without mainifold vacum something or other lol

i just dont want to go buying a fuel pump if i misunderstud something my pockets are very light these days thats all

cheers

[mike 850]

Installed another fuel pump I have, straight up to 2.5 bar! perfect then

Cheers