Engine 850: B5234T/2.3/20v/T5: - Maintaining Fuel Pressure Overnight

Jod T5 · Dec 22nd, 2008, 14:20

Hi
I am interested in getting some opinions on the workings of the Fuel Pressure Regulator and in particular how pressure is maintained overnight, if indeed it is at all....

The reason i ask is that my 760 takes a while to start, this is due to a defective check valve......

My 850 however also takes a while to fire although to the best of my knowledge all the sensors are working as they should be...

The car takes the same amount of time to start every morning (about 20 seconds) and when booted pulls without hesitation....This to me would show the pump, relay and filter is working fine....

There must be a valve to maintain the fuel up the pipe, be it part of the Pressure Regulator or a separate entity??

Any offers.....
cheers
Jod

Clan · Dec 22nd, 2008, 14:56

Hi Jod ,
When you turn off there is a valve at the front ( Part of the pressure regulator ) and a one way valve in the pump at the rear which stops the pressurised fuel leaking back to the tank through the pump or via the return line through the regulator . That should maintain the 3 bar pressure and hence stop the fuel boiling in the pipe/rail which would cause an air lock next time you start . The pressure must be maintained for 20 minutes , this gives time for the engine to cool enough so that vapour locks are not a problem ...

Jod T5 · Dec 22nd, 2008, 15:37

Quote:

Originally Posted by Clan

Hi Jod , When you turn off there is a valve at the front ( Part of the pressure regulator ) and a one way valve in the pump at the rear which stops the pressurised fuel leaking back to the tank through the pump or via the return line through the regulator . That should maintain the 3 bar pressure and hence stop the fuel boiling in the pipe/rail which would cause an air lock next time you start . The pressure must be maintained for 20 minutes , this gives time for the engine to cool enough so that vapour locks are not a problem ...

Thanks Nick, so there is two.....
I dont have equipment to check the fuel pressure when cold (dont fancy a face full of fuel from a tyre gauge lol) but i guess if i crack the inlet pipe at the joint in the morning, pressure will be obvious......
Are there any "tests" than carried out by someone with DIY tools...
Cheers
Jod

Clan · Dec 22nd, 2008, 15:49

The pressure wont be there in the morning BUT the pipes will be full with no air locks so as soon as the ignition turns on the pump will prime and raise the pressure in half a second . You need one of those screw on tyre valve adapters connected to some sort of gauge which reads up to about 5 bar . Volvo state the pressure should be a minimum of 2 bar ( I think ) up to 20 mins from hot ... after 20 mins it doesnt matter if it leaks away ... no easy way to check it ..

Jod T5 · Dec 22nd, 2008, 16:32

Quote:

Originally Posted by Clan

The pressure wont be there in the morning BUT the pipes will be full with no air locks so as soon as the ignition turns on the pump will prime and raise the pressure in half a second . You need one of those screw on tyre valve adapters connected to some sort of gauge which reads up to about 5 bar . Volvo state the pressure should be a minimum of 2 bar ( I think ) up to 20 mins from hot ... after 20 mins it doesnt matter if it leaks away ... no easy way to check it ..

More thanks..,
So even with no pressure as such with the fuel should still come out of the joint, clearly if there is none the fuel has dribbled back into the tank?...
Both my fuel pump relays (swapped at the weekend) both run for 5 seconds, priming the pressure sensor, this is from what i can gather excessive..
Once the car is running it pulls well which for me would eliminate the fuel pressure being an issue...?
Cheers
Jod

Clan · Dec 22nd, 2008, 18:14

I think if you press the valve and get a healthy squirt of fuel after say 20 mins then the non return valve and regulator will be ok .
The priming time has always been about 3 seconds right from the 1800E of 1970 , as long as it runs for a few seconds its fine . It's not really excessive because as soon as you engage the starter the pump will run again .. its not very often you leave the ignition on for 5 seconds before starting it ..

Dec 22nd, 2008, 14:20	#1
Jod T5 Phoenix from the ashes Last Online: Apr 24th, 2024 01:05 Join Date: Jan 2006 Location: Finchingfield	Maintaining Fuel Pressure Overnight Hi I am interested in getting some opinions on the workings of the Fuel Pressure Regulator and in particular how pressure is maintained overnight, if indeed it is at all.... The reason i ask is that my 760 takes a while to start, this is due to a defective check valve...... My 850 however also takes a while to fire although to the best of my knowledge all the sensors are working as they should be... The car takes the same amount of time to start every morning (about 20 seconds) and when booted pulls without hesitation....This to me would show the pump, relay and filter is working fine.... There must be a valve to maintain the fuel up the pipe, be it part of the Pressure Regulator or a separate entity?? Any offers..... cheers Jod __________________ Dum Spiro Spero VOC 20419

Dec 22nd, 2008, 14:56	#2
Clan Experienced Member Last Online: Jun 15th, 2024 16:06 Join Date: Jun 2007 Location: L/H side	Hi Jod , When you turn off there is a valve at the front ( Part of the pressure regulator ) and a one way valve in the pump at the rear which stops the pressurised fuel leaking back to the tank through the pump or via the return line through the regulator . That should maintain the 3 bar pressure and hence stop the fuel boiling in the pipe/rail which would cause an air lock next time you start . The pressure must be maintained for 20 minutes , this gives time for the engine to cool enough so that vapour locks are not a problem ... __________________ My comments are only based on my opinions and vast experience .

Dec 22nd, 2008, 15:49	#4
Clan Experienced Member Last Online: Jun 15th, 2024 16:06 Join Date: Jun 2007 Location: L/H side	The pressure wont be there in the morning BUT the pipes will be full with no air locks so as soon as the ignition turns on the pump will prime and raise the pressure in half a second . You need one of those screw on tyre valve adapters connected to some sort of gauge which reads up to about 5 bar . Volvo state the pressure should be a minimum of 2 bar ( I think ) up to 20 mins from hot ... after 20 mins it doesnt matter if it leaks away ... no easy way to check it .. __________________ My comments are only based on my opinions and vast experience .

Dec 22nd, 2008, 18:14	#6
Clan Experienced Member Last Online: Jun 15th, 2024 16:06 Join Date: Jun 2007 Location: L/H side	I think if you press the valve and get a healthy squirt of fuel after say 20 mins then the non return valve and regulator will be ok . The priming time has always been about 3 seconds right from the 1800E of 1970 , as long as it runs for a few seconds its fine . It's not really excessive because as soon as you engage the starter the pump will run again .. its not very often you leave the ignition on for 5 seconds before starting it .. __________________ My comments are only based on my opinions and vast experience .

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)