T6 running rough P0087 and P0088

[grubby mits]

Hi. 2008 T6. Just been serviced at my independent and now running rough - intermittent black exhaust smoke smelling of unburnt fuel. Codes showing are P0087 (fuel rail pressure too low) and P0088 (Fuel rail pressure too high). My immediate thought is a faulty fuel pressure sensor but I guess it may be a faulty pump. Have checked MAF and pressure sensor connections and both seem OK. I cant work out if the fuel pressure sensor regulates or just monitors the rail pressure. If it regulates pressure then how - is there a valve and return pipe somewhere for excess fuel return?

Once I know a bit more about how the system functions I may be more confident in the diagnosis.

TIA

GM

[Kev0607]

Originally Posted by grubby mits

Hi. 2008 T6. Just been serviced at my independent and now running rough - intermittent black exhaust smoke smelling of unburnt fuel. Codes showing are P0087 (fuel rail pressure too low) and P0088 (Fuel rail pressure too high). My immediate thought is a faulty fuel pressure sensor but I guess it may be a faulty pump. Have checked MAF and pressure sensor connections and both seem OK. I cant work out if the fuel pressure sensor regulates or just monitors the rail pressure. If it regulates pressure then how - is there a valve and return pipe somewhere for excess fuel return?

Once I know a bit more about how the system functions I may be more confident in the diagnosis.

TIA

GM

Why don't you bring it back to the garage? It was running fine before they serviced it.

Has the fuel filter been changed?

[grubby mits]

Hi Kev

If the fault was not with the garage I may be opening up an expensive can of worms if I take it back to them. No, fuel filter not changed at service.

A bit of research and head scratching leads me to the conclusion that the pressure relief valve/system is part of the pump assembly itself and not a relief valve and return pipe on the fuel rail. Today I will see if I can test the actual fuel pressure with a gauge - hopefully that will tell me if the sensor is faulty or not (if I can find out what the specified pressure range should be). If its not the sensor it looks like it must be the pump.

GM

[Kev0607]

I’d change the fuel filter in the first instance to see if that makes any difference.

[savabill]

Originally Posted by Kev0607

I’d change the fuel filter in the first instance to see if that makes any difference.

I think the t6 fuel filter is located in the tank, and is non serviceable.

[grubby mits]

Cleared the codes and took it for a run. Cold start fine; 5 mile run fine. Parked up and left it for 10 mins then re-started. Lumpy idle and black smoke; stalled on engaging "D". Managed to pull away using constant throttle pedal pressure (and brake pedal together to slow down/stop). Found a clear straight and put my foot down - flew like a bird and performed faultlessly until back home (so I don't think its a permanent fuel flow/blocked filter issue).

Downloaded codes again. Now P0191 (Fuel pressure sensor A circuit range/performance). Did some more research. Now pretty sure its a bad pressure sensor so I'll try that first, but I see others have been there before and a new sensor hasn't cured the problem.

I'll let you all know.

GM

[T5R92011]

Originally Posted by grubby mits

Cleared the codes and took it for a run. Cold start fine; 5 mile run fine. Parked up and left it for 10 mins then re-started. Lumpy idle and black smoke; stalled on engaging "D". Managed to pull away using constant throttle pedal pressure (and brake pedal together to slow down/stop). Found a clear straight and put my foot down - flew like a bird and performed faultlessly until back home (so I don't think its a permanent fuel flow/blocked filter issue).

Downloaded codes again. Now P0191 (Fuel pressure sensor A circuit range/performance). Did some more research. Now pretty sure its a bad pressure sensor so I'll try that first, but I see others have been there before and a new sensor hasn't cured the problem.

I'll let you all know.

GM

Don't pay over the odds for Fuel Pressure sensor...For T5s you can get the original Bosch ones for £30 approx so make sure you shop around. T6 sensor is probably very similar if not the same as T5.

[grubby mits]

Originally Posted by T5R92011

Don't pay over the odds for Fuel Pressure sensor...For T5s you can get the original Bosch ones for £30 approx so make sure you shop around. T6 sensor is probably very similar if not the same as T5.

Thanks for that. Will speak with the main dealer tomorrow but I THINK the Volvo boxed ones are IRO £100. There are plenty on line form £29.95 (mostly from Berlin based auto parts stores such as AUTODOC) but I can't believe the quality will be as good and there is a 10 day delivery wait. The part number I need is 31272732. Is that a match for the T5?

Thanks.

GM

[grubby mits]

Update:- I changed the sensor with a new one from Volvo today. The part No I got from VIDA for the T6 was 31272732 and this was the number of the new sensor the main dealer supplied. The part No of the old one I have just taken off is 30756097. The only visible difference between the two is the presence of as plastic "ear" to take a wiring clip. The Bosch number stamped on the case is 0 261 230 110.

Googling the Bosch number shows a much wider choice of sellers and lower prices. If anyone else needs to swap the fuel rail pressure sensor I recommend searching by the Bosch number rather than the Volvo part number.

I have fired up the engine and it is running fine - the codes have cleared. Test drive tomorrow!

GM