850 TDi 1996 FUEL PUMP OR RELAY PROBLEMS

kevj · Nov 3rd, 2008, 19:48

Hello all.

Have only just joined V.O.C. as i have only just bought a Volvo.!
Howevr all not good at the moment. Having problems with fuel supply. Car starts perfectly, and runs well to begin with, but then, after a few miles, starts to `hunt`, then loses power ,causing me to have to pull over and stop. a quick break, and restart usually resolves this, but only for a few more minutes, then back again. I understand there is a known problem with fuel pump relay contacts, but relay seems incredibly difficult to get access to ! Any help or comments appreciated. Is this relay or pump??

Kevj

warthog · Nov 3rd, 2008, 20:50

Hi Kev,

sorry to hear of your woes.

First thing I would do is change the fuel filter. It sounds as though the fuel delivery cannot keep up with the demand and this could indeed be a pump / relay problem, but the cheap thing first is the filter.

kevj · Nov 3rd, 2008, 21:26

thanks brian. have already changed filter today, didnt help at all i'm afraid. Do u or anyone else know how to access the relays on a TDI - they are almost impossible, or i am doing something wrong ! qiute possible.

kevj

warthog · Nov 4th, 2008, 17:28

Kev,

As far as I can tell, on the TDI there is no in-tank fuel pump as on the petrols (hence no 103 relay), instead the fuel injector pump draws the fuel itself from the tank via the filter. Thus the whole delivery side of the fuel system from tank to injector pump is under vacuum.

I have seen several times in the past on a variety of vehicles with this type of system, any slight imperfection in any of the flexible pipes or joint will allow air into the system well before any fuel leaks out. Although the system is self bleeding there could be a slow build up of air in the fuel pump causing the hunting you describe. Another thought is that if the return to tank line is blocked or the bleed valve in the top of the tank is not functioning correctly the system will either not completely self bleed or it will continue to draw bled air back into the delivery fuel line.

If the fuel tank is not venting properly, this could cause a partial vacuum in the tank and reduce the fuel flow into the injector pump. You could try running with the filler cap loose for a short while and see if the problem persists.

Those are my suggestions - any other ideas anyone?

cheers

kevj · Nov 9th, 2008, 20:40

Brian.
Thanks for the reply. Have spent a fair amount of time on this fault since my first posting. Situation now is as follows. Took car to my local garage, and they did some research, and found out that air leak was the problem. They tested the vacuum from the tank, and no apparent air leaks up as far as fuel filter. However, i have discovered that by replacing pipe before and after fuel filter, that pipe from tank to fuel filter is full of fuel, but lots of air in line from filter to injection pump. This led me to think that problem is the fuel filter housing leaking, or the non -return valve leaking air in, but a bit confused because when i linked feed pipes direct to bypass filter housing, lots of air isdrawn all the way from the fuel tank - not what i was expecting! any clues? does anyone know if there is a filter in the fuel tank?
into another week we go,

Kevj

warthog · Nov 9th, 2008, 21:06

Kev,

there shouldn't be any air in the fuel supply from the tank (obvious really!). I think there are two bits of flex pipe between tank and inlet to filter - one from tank to solid pipe that runs most of the way along the car and then another small flex. piece where the fuel pipe bends up around the bottom of the firewall. Either of these could be leaking.

There is a complicated valve arrangement on the fuel tank where both the return from the engine and the feed to the engine connect. This is where any air bled from the system re-enters the tank. If this valve is faulty then the air can be re-admitted into the feed circuit.

kevj · Nov 10th, 2008, 10:24

Thanka again Brian. You certainly know your stuff. Iam going to try and bypass feed from tank with a length of hose in filler neck, and thro to the filter, to see what happens. Will advise of outcone later.
Again, many thanks

Kevj

DieselDoNicely · Nov 11th, 2008, 12:27

Quote:

Originally Posted by kevj

Thanka again Brian. You certainly know your stuff. Iam going to try and bypass feed from tank with a length of hose in filler neck, and thro to the filter, to see what happens. Will advise of outcone later.
Again, many thanks

Kevj

Fuel Injection Services, Cardiff for a pump recon, mine was leaking fuel about 60,000 miles ago, they charged about £170 to change the seals etc. Shorts the Bosch place in Swansea wanted £800.

You need to take the pump off and send it to tham as they dont do that side of it.

microbus · Nov 11th, 2008, 13:37

I have the same problem although somewhat more intermittent than the problems you describe. I get to do about 2-3000 miles and then I get the "hunting" you decribe and a bet of over revving at which point pressing the accelerator elicits no response, followed by engine management light coming on and engine then dies. Engine will restart after a few mins and then will run with a bit of rough idle (at low revs) for a while until engine management light goes off. Then I wait until the next time. Other then that issue I love this car.

Have taken car to main dealer for diagnosic, no issues identified. Running perfectly they said. Took car to Bosch specialist, who found pump timing out, but this has not remedied problem.

Have been down the route of replacing pump, which with removal and fitting will cost an arm and a leg, given the cars current value. I have followed Diesel Bobs recommendation re the Swansea diesel fitter. They very helpful and comparably cheap. Very quick turn around time as well.

I hope you get your problems sorted.

warthog · Nov 11th, 2008, 17:13

Microbus,

from experience you have the classic symptoms of air in the fuel. The rev symptom is caused by a facet of the rotary fuel injection pump and how it meters the fuel to the injectors. When these pumps try to pump fuel with air in it, the differences in compressibility between air and fuel really upset the pressure balance in the pump sometimes causing a very sensitive throttle response until the air is cleared out. ( a previous big diesel I had was almost undriveable round town when this happened - the power went from idle to wheel-spin with a feather touch on the throttle!). The hunting is quite possibly also a facet of this poor fuel metering along with chunks of air instead of fuel being delivered to the engine.

On these types of systems where the whole fuel system upstream of the pump is under vacuum, any defect in the fuel lines or connections will allow air to enter long before fuel will leak out. The best way I've shown this is to incorporate a piece of clear fuel pipe into the line just before the pump. Any air in the fuel will show up.

If you are changing the flexible fuel lines for clear piping it's very important that you get fuel resistant hose as the common types that are available are Ok for air and water but quickly harden with fuel and then don't seal at all.

Nov 3rd, 2008, 19:48	#1
kevj New Member Last Online: May 6th, 2009 09:59 Join Date: Nov 2008 Location: NEWTON ABBOT	850 TDi 1996 FUEL PUMP OR RELAY PROBLEMS Hello all. Have only just joined V.O.C. as i have only just bought a Volvo.! Howevr all not good at the moment. Having problems with fuel supply. Car starts perfectly, and runs well to begin with, but then, after a few miles, starts to `hunt`, then loses power ,causing me to have to pull over and stop. a quick break, and restart usually resolves this, but only for a few more minutes, then back again. I understand there is a known problem with fuel pump relay contacts, but relay seems incredibly difficult to get access to ! Any help or comments appreciated. Is this relay or pump?? Kevj

Nov 3rd, 2008, 20:50	#2
warthog VOC Member Last Online: Oct 30th, 2021 14:51 Join Date: Dec 2001 Location: Bristol	Hi Kev, sorry to hear of your woes. First thing I would do is change the fuel filter. It sounds as though the fuel delivery cannot keep up with the demand and this could indeed be a pump / relay problem, but the cheap thing first is the filter. __________________ Brian '96 T5 Estate Auto

Nov 4th, 2008, 17:28	#4
warthog VOC Member Last Online: Oct 30th, 2021 14:51 Join Date: Dec 2001 Location: Bristol	Kev, As far as I can tell, on the TDI there is no in-tank fuel pump as on the petrols (hence no 103 relay), instead the fuel injector pump draws the fuel itself from the tank via the filter. Thus the whole delivery side of the fuel system from tank to injector pump is under vacuum. I have seen several times in the past on a variety of vehicles with this type of system, any slight imperfection in any of the flexible pipes or joint will allow air into the system well before any fuel leaks out. Although the system is self bleeding there could be a slow build up of air in the fuel pump causing the hunting you describe. Another thought is that if the return to tank line is blocked or the bleed valve in the top of the tank is not functioning correctly the system will either not completely self bleed or it will continue to draw bled air back into the delivery fuel line. If the fuel tank is not venting properly, this could cause a partial vacuum in the tank and reduce the fuel flow into the injector pump. You could try running with the filler cap loose for a short while and see if the problem persists. Those are my suggestions - any other ideas anyone? cheers __________________ Brian '96 T5 Estate Auto

Nov 9th, 2008, 21:06	#6
warthog VOC Member Last Online: Oct 30th, 2021 14:51 Join Date: Dec 2001 Location: Bristol	Kev, there shouldn't be any air in the fuel supply from the tank (obvious really!). I think there are two bits of flex pipe between tank and inlet to filter - one from tank to solid pipe that runs most of the way along the car and then another small flex. piece where the fuel pipe bends up around the bottom of the firewall. Either of these could be leaking. There is a complicated valve arrangement on the fuel tank where both the return from the engine and the feed to the engine connect. This is where any air bled from the system re-enters the tank. If this valve is faulty then the air can be re-admitted into the feed circuit. __________________ Brian '96 T5 Estate Auto

Nov 11th, 2008, 17:13	#10
warthog VOC Member Last Online: Oct 30th, 2021 14:51 Join Date: Dec 2001 Location: Bristol	Microbus, from experience you have the classic symptoms of air in the fuel. The rev symptom is caused by a facet of the rotary fuel injection pump and how it meters the fuel to the injectors. When these pumps try to pump fuel with air in it, the differences in compressibility between air and fuel really upset the pressure balance in the pump sometimes causing a very sensitive throttle response until the air is cleared out. ( a previous big diesel I had was almost undriveable round town when this happened - the power went from idle to wheel-spin with a feather touch on the throttle!). The hunting is quite possibly also a facet of this poor fuel metering along with chunks of air instead of fuel being delivered to the engine. On these types of systems where the whole fuel system upstream of the pump is under vacuum, any defect in the fuel lines or connections will allow air to enter long before fuel will leak out. The best way I've shown this is to incorporate a piece of clear fuel pipe into the line just before the pump. Any air in the fuel will show up. If you are changing the flexible fuel lines for clear piping it's very important that you get fuel resistant hose as the common types that are available are Ok for air and water but quickly harden with fuel and then don't seal at all. __________________ Brian '96 T5 Estate Auto

Nov 3rd, 2008, 21:26	#3
kevj New Member Last Online: May 6th, 2009 09:59 Join Date: Nov 2008 Location: NEWTON ABBOT	thanks brian. have already changed filter today, didnt help at all i'm afraid. Do u or anyone else know how to access the relays on a TDI - they are almost impossible, or i am doing something wrong ! qiute possible. kevj

Nov 9th, 2008, 20:40	#5
kevj New Member Last Online: May 6th, 2009 09:59 Join Date: Nov 2008 Location: NEWTON ABBOT	Brian. Thanks for the reply. Have spent a fair amount of time on this fault since my first posting. Situation now is as follows. Took car to my local garage, and they did some research, and found out that air leak was the problem. They tested the vacuum from the tank, and no apparent air leaks up as far as fuel filter. However, i have discovered that by replacing pipe before and after fuel filter, that pipe from tank to fuel filter is full of fuel, but lots of air in line from filter to injection pump. This led me to think that problem is the fuel filter housing leaking, or the non -return valve leaking air in, but a bit confused because when i linked feed pipes direct to bypass filter housing, lots of air isdrawn all the way from the fuel tank - not what i was expecting! any clues? does anyone know if there is a filter in the fuel tank? into another week we go, Kevj

Nov 10th, 2008, 10:24	#7
kevj New Member Last Online: May 6th, 2009 09:59 Join Date: Nov 2008 Location: NEWTON ABBOT	Thanka again Brian. You certainly know your stuff. Iam going to try and bypass feed from tank with a length of hose in filler neck, and thro to the filter, to see what happens. Will advise of outcone later. Again, many thanks Kevj

Nov 11th, 2008, 13:37	#9
microbus New Member Last Online: Sep 17th, 2019 22:15 Join Date: Jul 2008 Location: Sheffield	I have the same problem although somewhat more intermittent than the problems you describe. I get to do about 2-3000 miles and then I get the "hunting" you decribe and a bet of over revving at which point pressing the accelerator elicits no response, followed by engine management light coming on and engine then dies. Engine will restart after a few mins and then will run with a bit of rough idle (at low revs) for a while until engine management light goes off. Then I wait until the next time. Other then that issue I love this car. Have taken car to main dealer for diagnosic, no issues identified. Running perfectly they said. Took car to Bosch specialist, who found pump timing out, but this has not remedied problem. Have been down the route of replacing pump, which with removal and fitting will cost an arm and a leg, given the cars current value. I have followed Diesel Bobs recommendation re the Swansea diesel fitter. They very helpful and comparably cheap. Very quick turn around time as well. I hope you get your problems sorted.

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