Hello, I hope I can offer you some assistance.
The fault code P251A won't be the reason for the loss of power, this fault code relates to a Power Take Off (PTO) circuit, this fault will have been logged in error from a previous software update on the engine management control module.
You need to have the software checked and updated as necessary but make sure all necessary parameters are entered when required.
With regard to the actual loss of power check for stored fault codes when the fault occurs. If no fault codes are stored then you need to check live data from the engine management when the fault occurs, check the fuel pressure demanded and actual any discrepancy of around 20 bar will result in the engine management switching to Limited Operating. Check that the pressure relief valve hasn't activated in the end of the fuel rail if it has then the engine management won't be able to control the fuel pressure. Replace the fuel filter if it hasn't been replaced recently, if possible check the injector operation as a faulty injector will cause fuel pressure concerns.
Check the EGR valve operation, if you can't hear it cycle at ignition off it may have seized although this normally leaves a fault code.
Let me know if I can assist further and I'll reply to you as soon as I'm able to.
Best wishes and merry Christmas,
the fuel filter is new about 3 months a go my solus pro reads in kpa can you please tell me the paramters for fuel pressure and how to test the sensor
the fuel pressure at idle should be around 300bar, you should be able to see the demanded fuel pressure to check the actual pressure against this. If you disconnect the fuel pressure sensor from the rail you should get a maximum fuel pressure reading, if not there may be a wiring concern. 1 bar is equal to 100kpa.
As I said originally if there is a discrepancy between the pressure demanded and actual then the fuel rail pressure relief valve may have activated.
As the only code you have is the PTO as I said earlier make sure the engine management software is up to date.
Let me know if I can assist any further.
hi, yes the software was updated in september 2011
the fuel pressure at idle is around 350 PSI
but there is a huge difference between psi and bar is it defently 300 bar or 300 psi on the F P Rail
i disconected the FPS and what you said would happen did
how do i test the fuel rail pressure relief valve has been activated????
the engine does not go in to limited opperating mode all the time - it is very sporadic when it hapens mainly when the mini bus has 9 passengers in and some luggage in the boot dont know weather it is a co-incidence or related to extra weight and more throttle useage ???
I think the reading you have is incorrect 300PSI is only around 20 bar which the engine wouldn't even start on, the target pressure to start is at least 250 bar and at idle is around 300 bar. The figures I give to you are in bar for certain.
If you think, 300 PSI pressure would not even be enough to overcome the compression pressure in the cylinder (TDCi compression should be around 350 to 370 PSI) hence the extreme pressures involved in the fuel system the pressure can exceed 600 bar if not controlled.
If you can read live data while driving then check the fuel pressure as follows,
select second gear when driving allow the engine to come to idle in second gear then accelerate hard up to 4000 RPM then release the throttle observe the fuel pressure when you do this if the pressure reaches 500 bar then the fuel pressure relief valve has opened.
Double check the fuel pressure reading as I say 20 bar wouldn't start the engine.
Let me know,
i have done the test you sugested
here are the results
at 4000 rpm in 2nd gear = 169120 kpa which converts to 1691.2 bar
what do you think?
has the valve been activated
the driver has noticed a drop in fuel ecomomy is this related?
as the pressure reaches 1600 bar then I would say the relief valve is OK as if the relief valve opens the pressure is normally stable at 500 bar.
Is the fault evident when you test the van at all?
no every time i have driven the vehicle i have not been able to replicate the symtoms
what is injector clylinder ballance?
injector cylinder 1 and 4 is at 2 and 2 and 3 are at 0 is this correct?
injector cylinder 1 and 4 is at 2 and 2 and 3 are at 0 is this correct? #
injector balance is measuring the adjustment of the fueling for the injectors normally the readings are around 0.9 to 2 so I would say that these were OK.
You really need to measure things like the fuel pressure when the fault occurs, this can mean using the van over several days. A reading that is correct now may well show incorrectly when the fault occurs.
Let me know if I can help further.