DOHC fueel pressure

[voucht]

Hi,
I'm going to fit an adjustable fuel pressure regulator. But I have hard time finding at what pressure it should be adjusted. what is the correct fuel pressure in the injection ramp of my engine : 2.0i DOHC (Sierra/Scorpio) ?

The Haynes service and repair manual says:

[...]
General
Fuel tank capacity (all models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60.0 litres (13.1 gallons)
Fuel octane rating:
Leaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 RON (4-star)
Unleaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 RON (Premium)
*Models fitted with a catalytic converter must be operated on unleaded fuel at all times. Do not use leaded fuel in such models, as the catalyst will
be destroyed:
System control pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 bar
System type:
2.0 litre SOHC models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bosch L-Jetronic
2.0 litre DOHC models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multi-point fuel injection system, controlled by EEC IV engine
management system
[...]

Is the "System control pressure" (2.5 bar) the correct working fuel pressure ?

If it is not, does anyone know what is the correct working pressure please, or could tell me a rough value to start with the tuning?

Thanks a lot.

[flyerncle]

Is there a vacuum pressure regulator in the system/in fuel rail.

That regulates it by engine demand/vac in manifold,the system pressure can only be max pump output at no demand.

[baz-r]

"That regulates it by engine demand/vac in manifold,the system pressure can only be max pump output at no demand."

er that dont sound right

there is two ways of looking at it with the vac pipe disconected or engine not running or manifold at atmosperic pressure you get base fuel pressue this is the quoted pressue of the regulator

the pressure in the vac pipe changes it by a factor of 1:1 so if you had a 3bar reg and -0.5bar vac the fuel pressure will be 2.5 bar if you have a turbo car it will raise pressure above this base value

its to keep the fuel flow at an equal flow rate at the injector nozzle as the maifold pressue is sucking it ot or pushing it back in on a turbo

max pump output will be 9 bar or so the reg vents fuel back to tank to regulate pressure

i would say 2.5bar base by the sound of it and older injection systems usualy run sub 3 bar

[twinturbo]

yeah 2.5 bar is the fuel rail pressure.

TT

[voucht]

Thank you for the replies, very useful to me.
I want to fit an adjustable fuel pressure regulator because it looks like I have too much fuel going into the combustion chambers : some fuel is apparently not burnt, I can see that to the smell, black smoke indicating a bad combustion, and to the colour of the spark plugs. I checked the ignition and everything seem to be working normally there.
If the OEM fuel pressure regulator is not functioning correctly, and there is too much pressure in the rail, can the injector inject too much fuel in the chamber? Or is the quantity of fuel injected limited by the injector size anyway, and what ever the pressure is in the rail, the same quantity of fuel is injected?
Sorry for my complete lack of knowledge when it come to this matter :o
Thank you very much.

[flyerncle]

Quantity of fuel injected is controlled by the amount of time the injector is open and pressure applied to it,modern systems vary the width of the pulse sent to the injector via the ecu to vary the amount of fuel for a given engine condition and load/temp/maf etc.

The temp switch could be faulty fooling the ecu thinking it needs more fuel,and if there is a sensor in the inlet for air temp that may be faulty,mangaged to dodge Ford fuel injection system for years until now after working on the old jetronic systems a million years ago !:eek: