Lack of Power throughout rev range

Hi hoping someone can help, got a 2003 td4 that lacks power. It seems as if it is under fueling. Maf was changed with new Bosch item as the one that was fitted had a broken temp wire, also replaced map sensor. If you put your foot down the revs climb gradually in every gear but the higher the gear the slower it gets up to speed. No faults appear on code reader.

Taken voltage readings at fuel rail sensor, shows .5 volts ignition on, 1.3 volts at tick over and 3 volts at 3000 r.p.m

Readings from low pressure senor (fuel pipe in engine bay that comes from rear fuel pump next to rear wheel arch) Shows 4 volts at tick over but drops to 3 volts at 3000 r.p.m.

Have checked all vaccum pipes etc. The turbo lingage is free and operates correctly. Pump the throttle and you can see actuator operate correctly. At higher revs you can hear turbo spool up etc.

Any pointers would be appreciated

From previous fault finding I seem to remember that low pressure sensor reading should remain very close to 4v at 3000rpm. What mileage has the LP pump done, ever been replaced?

Chaser
Not sure if pump has been replaced it has one pump by the rear wheel arch. That was my first thought but a mechanic friend said that if the pump is weak it would result in non starting issues. Have to say not sure he is right, my train of thought is if the fuel supply is weak the ecu will only deliver fuel it knows it is getting to prevent non running engine. May be ecu's are not that clever? Sorry the frelander has done 82K miles.

Most common symptom of a weak pump is lack of power on hills etc. when demand is high. Pumps can also fail completely which results in non start. The ecu will limit fueling to engine to try to maintain pressure in the rail to get you home. Age and mileage is about right for the end of life of a pump from what I see on here and elsewhere. Tough call cos they're quite expensive but voltages seem to suggest low pressure.

Fuel filter changed ??

Yip that what I thought would happen, I have changed pump on Disco but that let you know when it was going as whined like billio. The freelander pump makes a bit of noise when you turn on ignition but I think most make a priming kind of noise I think.

Got fuel filter but not put on yet, my chum is going to check pressures etc tomorrow to see if that gives us a clue. But I think pump is number one on the list if it limits fuel etc. There is no smoke what so ever even if you floor it whicjh again points at fueling. I dont mind if it is the pump as do not want to get into the trap of replacing bits as a process as I know some people have. So heres hoping

Well we put the freelander on diagnostics took it for a drive and the supply pressure dropped but the fuel rail pressure looked OK. Anyway fitted new pump (non oem) and new filter. However pump whines which is not unusual as its priming but it continues to whine even while engine is running. Will check outputs tomorrow, the plot thickens.

There have been a few complaints of cheap pattern pumps being noisy. A bit late now but should have gone for OEM..

Right checked both pumps the BMW one we took off is fine good flow rate etc. The new one also has good flow rate but as you say a little noisy.

So what next? There must be a sensor somewhere that is not allowing pump to throw fuel in?

The fact the high pressure fuel rail sensor go's up to 3 volts at 3000 rpm instead of the quoted 2 volts would tis influence the ECU or could ECU be corrupt. Just a tad strange that no faults are logged?

As you say 3v @ 300rpm is too high. I could only speculate as to the effect that would have on ecu and fueling. Thoughts are if the ecu is seeing a false reading and the actual rail pressure is lower than the reading then injection duration and therefore quantity will be too low. Faulty sensor perhaps?

There are known bad connection issues with the harness to the rail pressure sensor that cause low voltage readings at the ecu but don't know if it that would confuse the ecu and fuel pressure regulator on the HP pump and explain high pressure/readings at the rail.

Chaser
Not done much more, although yesterday did a leak back test. Made up four tubes etc disconnected injector wiring clamped off return hose. Cranked for about 5-10 seconds and each tube filled up woth about 6cm of diesel? As I cranked you could see it going up the tube. But it starts fine maybe a little cranking but no more than a couple of seconds. Would this cause thae lack of power?

I think you would have poor starting symptoms from leaky injectors before any noticeable loss of power. would also expect to see some white smoke from the low injection pressure and poor atomisation.

thinking of a different approach, try running with the maf disconnected in case there is an issue with the replacement.
check exhaust system is undamaged and clear.
clean and disable egr valve.

Are you getting a steady 4v/3000rpm at low pressure sensor now? if not I still wouldn't rule out Lp pump.

Right finally spent some time with mechaninc mate and his testing kit. Still no faults, but one area that showed up as a possible problem was low pressure fuel supply. We put pressure gauge on just before LP sensor. It read 2.5 bar at tickover but dropped to 2 bar when revved. So we then attached gauge just after fuel filter where it read 3 bar and dropped to 2.5 bar when revved? Is this within parameters? Every thing else seemed to be OK. Injectors where satisfactory well within tollerences. Was difficult to messure boost but got up to about 1.5 bar but guess this is because there is fuelling issue. Bit like chicken egg though no boost no fuel no fuel no boost.

Any more suggestion much appreciated

Pressure alone isn't enough, what is equally important is flow rate. If the fuel pressure drops when revving the engine of a stationary vehicle then at higher rpm and load when flow demand is much greater there will be a greater pressure drop which would indicate the pump can't keep up the required flow.

No guarantees but if it were me I'd try a new pump, I know you won't want to waste money on a wrong diagnosis but at this age and mileage it's due to fail anyway.