Fuel Pressure Question

[Sean Nugent]

Volvo S70 2.5T

Does anyone know if, when the accelerator is floored, the volvo ECU
increases the fuel pressure to the injectors and thus increases the
amount of fuel entering the engine for the time the injector is open.
This is as opposed to just opening the injevtors for longer...

ie is fuel pressure at all dependant on revs etc.....

Sean

 

[Mike F]

Volvo S70 2.5T

Does anyone know if, when the accelerator is floored, the volvo ECU
increases the fuel pressure to the injectors and thus increases the
amount of fuel entering the engine for the time the injector is open.
This is as opposed to just opening the injevtors for longer...

ie is fuel pressure at all dependant on revs etc.....

Sean

No, fuel pressure in dependant on intake manifold pressure. So under
light load when there's lots of vacuum the fuel pressure is lower than
high load when there's turbo boost. However, the fuel pressure is kept
at a constant amount above intake manifold pressure, so the amount of
injected fuel is determined only by injector opening time.

 

[Tim..]

Volvo S70 2.5T

Does anyone know if, when the accelerator is floored, the volvo ECU
increases the fuel pressure to the injectors and thus increases the
amount of fuel entering the engine for the time the injector is open.
This is as opposed to just opening the injevtors for longer...

ie is fuel pressure at all dependant on revs etc.....

The fuel pressure reg on the injector rail is connected to the inlet
manifold where it can sense manifold pressure so that fuel pressure is kept
at a constant value above intake pressure. Therefore for the same injector
duration fuel delivered will be the same irelevant to intake pressure.

The ECU merely fires the injectors for different time periods depending on
engine speed and operating conditions to vary the fuelling.

During certain circumstances the ecu will halve the firing time but double
the number of shots per cycle, typically during cranking, and at this time
it also ignores the CPS and fires all the injectors once per crankshaft
revolution.

Tim..

 

[Sean Nugent]

No, fuel pressure in dependant on intake manifold pressure. So under
light load when there's lots of vacuum the fuel pressure is lower than
high load when there's turbo boost. However, the fuel pressure is kept
at a constant amount above intake manifold pressure, so the amount of
injected fuel is determined only by injector opening time.

So - I was wrong about the ECU - but right about the effect which
would explain the problem I have.

I have an LPG system on the car that takes the petrol injector pulse,
ups it by a % to account for the gas and then squirts gas for that
time into the cylinder. However it ignores the manifold pressure - the
gas pressure remains constant.

Sean