Air in diesel system, noisy UBP with 3\4 full tank.

paulf · 19th August 2014, 13:23

I am having a problem with air in the fuel system on my diesel.I have been running with no intank pump for over a year and recently it started taking longer to start and the UBP was noisy even when 3\4 full with fuel..I decided to fit the spare new under bonnet pump that i had in the boot and have found that it still is hard to start and when I removed the fuel line it had a lot of air coming through with the fuel and only pumped about a litre of fuel in the minute that it runs for.I have checked under the bonnet for any leaky pipes in case it was pulling in air but all seems ok, the only other way i can see of air being in the system is if it is being pulled in at the fuel tank end bur cant think how it would when above half full.
I could obtain and fit a new in tank pump but not certain the fault is because of this as i have ran for well over a year with out it working.
Paul

James.uk · 19th August 2014, 16:22

Replace the underbonnet and the intank pumps and see how the car runs.

If it still plays up get back to us please.

...

Mike Noc · 19th August 2014, 16:26

And replace the fuel filter if you haven't got a record of it being done.

paulf · 19th August 2014, 16:59

I wish it was that simple, am aware of the usual problems and have now traced the reason for the air in the system to be due to the valve assembly on the fuel cooler at the back of the car leaking.I now need to bypass it to get the car running again and then find a replacement.
Paul

Trevor1975 · 19th August 2014, 21:13

Quote:

Originally Posted by paulf

I wish it was that simple, am aware of the usual problems and have now traced the reason for the air in the system to be due to the valve assembly on the fuel cooler at the back of the car leaking.I now need to bypass it to get the car running again and then find a replacement.
Paul

Mine also has a new UBP and is noisy - sounds like air in the system.

Will check out my fuel cooler... bypassing sounds like an option

paulf · 19th August 2014, 22:11

Well I realised that the fuel cooler thermostat appeared to be where the leak was coming from and having removed it, it also appears that it doesn't work.
It has three ports and all are full open to each other at normal ambient temperature, as I understand it there should be one or the other outlets open either to the fuel cooler rad or direct to the fuel manifold next to it. I think that the air is being drawn back in from the tank return due to this, I am therefore going to have to remove the whole assembly and directly join the fuel flow and return pipes rather than just link out the rad.If it works then I will have to find a replacement unit somehow.

Quote:

Originally Posted by paulf

I wish it was that simple, am aware of the usual problems and have now traced the reason for the air in the system to be due to the valve assembly on the fuel cooler at the back of the car leaking.I now need to bypass it to get the car running again and then find a replacement.
Paul

Mike Noc · 19th August 2014, 22:14

Here's a sketch of the fuel cooler plumbing. Hope it helps.

http://www.the75andztclub.co.uk/foru...d.php?t=172055

To bypass the thermostat and fuel cooler connect the spill return line to the restrictor valve and blank off the pipe to the cooler.

.

paulf · 20th August 2014, 10:45

I have found that the thermostat is open in all flow directions and offers no resistance to flow so is obviously faulty, having removed the whole assembly I found that the restrictor valve assembly is not at least on my car it is just a 5 way connector with all ports connected together.I have now simply joined the supply and return lines and the car now runs but wont rev above 3000 rpm, I am wondering whether the new under bonnet pump is not supplying sufficient pressure or whether i now need to restrict the back flow to the tank as there is a good flow of fuel in both directions now.

Mike Noc · 20th August 2014, 11:19

The 5 port connector should have a smaller diameter restricted internal port between the supply and return channels. Have you still got it in the circuit?

If it won't rev past 3000 then it is in limp mode due to there not being enough LP fuel pressure.

Try putting everything back as it was and then connecting the spill return line going into the thermostat directly to the fuel cooler, and blanking off the line from the thermostat to the 5 port connector.

.

paulf · 20th August 2014, 21:24

I have temporarily refitted the plastic restrictor and it now runs normally, I need to clean the radiator as it would not have had much cooling effect due to being completely blocked with mud etc.After doing so I will refit it minus the thermostat and expect it to run as it did before the problems. I dont think that the thermostat was working at all and the outer hosing was leaking which was where the air was getting into the system, so assume that if the cooler is permanently in the return circuit it wont do any harm.
Paul

19th August 2014, 13:23	#1
paulf Avid contributor Rover 75 CDT Connoisseur 1999, 2004 cdti connosieurur Join Date: Aug 2009 Location: Kettering Posts: 181 Thanks: 0 Thanked 6 Times in 5 Posts	Air in diesel system, noisy UBP with 3\4 full tank. I am having a problem with air in the fuel system on my diesel.I have been running with no intank pump for over a year and recently it started taking longer to start and the UBP was noisy even when 3\4 full with fuel..I decided to fit the spare new under bonnet pump that i had in the boot and have found that it still is hard to start and when I removed the fuel line it had a lot of air coming through with the fuel and only pumped about a litre of fuel in the minute that it runs for.I have checked under the bonnet for any leaky pipes in case it was pulling in air but all seems ok, the only other way i can see of air being in the system is if it is being pulled in at the fuel tank end bur cant think how it would when above half full. I could obtain and fit a new in tank pump but not certain the fault is because of this as i have ran for well over a year with out it working. Paul

19th August 2014, 22:14	#7
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,548 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	Here's a sketch of the fuel cooler plumbing. Hope it helps. http://www.the75andztclub.co.uk/foru...d.php?t=172055 To bypass the thermostat and fuel cooler connect the spill return line to the restrictor valve and blank off the pipe to the cooler. . Last edited by Mike Noc; 20th August 2014 at 12:22..

20th August 2014, 11:19	#9
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,548 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	The 5 port connector should have a smaller diameter restricted internal port between the supply and return channels. Have you still got it in the circuit? If it won't rev past 3000 then it is in limp mode due to there not being enough LP fuel pressure. Try putting everything back as it was and then connecting the spill return line going into the thermostat directly to the fuel cooler, and blanking off the line from the thermostat to the 5 port connector. . Last edited by Mike Noc; 20th August 2014 at 13:54..

19th August 2014, 16:22	#2
James.uk Passed Away 2002 Pale Blue. Rover 75 CDTi Connoisseur auto. 170K miles Join Date: Dec 2008 Location: Near the M67. Posts: 14,509 Thanks: 199 Thanked 585 Times in 397 Posts	Replace the underbonnet and the intank pumps and see how the car runs. If it still plays up get back to us please. ...

19th August 2014, 16:26	#3
Mike Noc This is my second home Rover 75 CDT Manual Connoisseur SE, Rover 75 CDT Automatic Connoisseur SE & a Freelander Td4. Join Date: Jul 2009 Location: Hampshire Posts: 11,548 Thanks: 3,470 Thanked 3,119 Times in 2,247 Posts	And replace the fuel filter if you haven't got a record of it being done.

19th August 2014, 16:59	#4
paulf Avid contributor Rover 75 CDT Connoisseur 1999, 2004 cdti connosieurur Join Date: Aug 2009 Location: Kettering Posts: 181 Thanks: 0 Thanked 6 Times in 5 Posts	I wish it was that simple, am aware of the usual problems and have now traced the reason for the air in the system to be due to the valve assembly on the fuel cooler at the back of the car leaking.I now need to bypass it to get the car running again and then find a replacement. Paul

20th August 2014, 10:45	#8
paulf Avid contributor Rover 75 CDT Connoisseur 1999, 2004 cdti connosieurur Join Date: Aug 2009 Location: Kettering Posts: 181 Thanks: 0 Thanked 6 Times in 5 Posts	I have found that the thermostat is open in all flow directions and offers no resistance to flow so is obviously faulty, having removed the whole assembly I found that the restrictor valve assembly is not at least on my car it is just a 5 way connector with all ports connected together.I have now simply joined the supply and return lines and the car now runs but wont rev above 3000 rpm, I am wondering whether the new under bonnet pump is not supplying sufficient pressure or whether i now need to restrict the back flow to the tank as there is a good flow of fuel in both directions now.

20th August 2014, 21:24	#10
paulf Avid contributor Rover 75 CDT Connoisseur 1999, 2004 cdti connosieurur Join Date: Aug 2009 Location: Kettering Posts: 181 Thanks: 0 Thanked 6 Times in 5 Posts	I have temporarily refitted the plastic restrictor and it now runs normally, I need to clean the radiator as it would not have had much cooling effect due to being completely blocked with mud etc.After doing so I will refit it minus the thermostat and expect it to run as it did before the problems. I dont think that the thermostat was working at all and the outer hosing was leaking which was where the air was getting into the system, so assume that if the cooler is permanently in the return circuit it wont do any harm. Paul