D4 faulty fuel pump

[wombathole]

My D4 3.0 has stopped suddenly twice in the first 6 weeks of ownership. Land Rover believe its a faulty fuel pump.

They say the fuel tank is a saddle shape with a fuel feeder on each side, and one of mine is not working. Does anyone have any diagram or knowledge of the shape of the fuel tank and type of fuel pumps?

My fuel gauge has never gone below 3/8 or had the red light come on, even though the engine stops from not getting enough fuel. I'm thinking this is because half the tank is still full, so the gauge gets confused. Any one seen this before? Is the fuel pump and the fuel gauge sender in the same unit? What is the logic of the digital fuel gauge, getting feeder signals from both sides of the saddle? How does it arbitrate the information to display it on the dash? Where is the logic the drives the red fuel light?

Lastly, a more generic question about the common rail system. How many fuel pumps are there in the total system? My assumption is; 2 low pressure, high volume pumps in the tank moving the fuel forward, then 1 high pressure, low volume pump in the engine bay pressurising the common rail. Anyone got any diagrams or technical description of the system? My assumption could be totally incorrect.

Thanks in advance for any help. FYI, Land Rover's ordering 2 new fuel pumps for the tank, which they think it going to rectify the issue. Time will tell.

Andy

[wombathole]

FYI for those following this thread, update I was given from LR yesterday.

D4 has saddle fuel tank, drain tube between low points, 1 low pressure, high volume electric pump in tank, 1 mechanically driven high pressure, low volume tank at engine pressurising the common rail, 2 fuel gauge sender units in the tank (1 in each low point). Why 1 pump but 2 senders when there is the drain tube??? Sounds a bit weird to me.

I'm told my fuel pump and one sender unit works. The other sender is faulty. Waiting on replacement to arrive.

To me, the faulty fuel sender explains why my digital fuel gauge is not reading correctly, fuel consumption calculator may be totally wrong and distance to empty calculator is totally wrong and i believe the replacement will fix there issues, but that is all cosmetic. At this time, LR cant give a satisfactory answer as to why my engine shuts down once after 520Km, another time after 440km from full tank, seemingly by running out of diesel... (with 2 kids under 5, my wife was not all that happy with LR and me when she was stuck on the side of the road for 1.5 hours!)

Could i truly be running out of fuel? Has anyone recorded 20+L/100km city driving in the D4 3.0? From the manual calculations i've done when we fill it up, i believe we are getting ~14 city, ~10 country, ~14 deep sand. Haven't had it long enough to do mud and mountains yet.

Alternatively, any ideas how a fuel gauge sender unit could confuse the computer to think its out of fuel (when its not) and shut down the engine?

Any other ideas?

Do you want more updates on this topic when I hear from LR and get my new car back in a working order?

Andy

PS: In the mean time, i'm driving their Freelander 2 TD4 auto. What a great little wagon! A huge difference compared to the FL series 1 i drove a few years back. For trips and real 4wding its not the answer, but for the city driving which we do 90% of the time, this little thing is very impressive. Engine sounds like a 90's tin can diesel but performance is great, 10L/100km city, very comfortable cabin (especially the front seats!), looks good out and in, little car but maintains the LR great visibility / commanding driving position and large enough for the 2 baby seats and 2 strollers in the back. Would be a very good choice as a second vehicle, but i haven't done any research into price competitiveness in that small SUV market.

PPS: LR service is doing a good job; keeping me informed, explaining the details to the level i want to hear and providing the FL2 until the D4 is fixed.

[Dingmark Jim]

My understanding of most fuel consumption rate calculators (have a relative who is an auto design engineer - this is what he says) in diesel engines is that they don't use the fuel tank level, and also don't have any type of flow meter in a flowline (which would cost a fortune). What they do is input the common rail pressure, engine speed, vehicle speed and throttle position (which relates to how much of the time the injectors are flowing fuel into the combustion chambers). From this they infer fuel consumption. It's the same input data (except vehicle speed) which goes into the computer which decides how long the injectors are open. Providing one or more injectors don't have a partial obstruction, the calculation of fuel consumption is very consistent, but not terribly accurate. In other words, if a D3 computer is showing 10.0 litres/100 kms, but in reality is really burning 12.2 litres/100km, then every time the computer is showing 10.0, it is really burning 12.2. Some errors are introduced as this is an approximate calculation, eg, as fuel heats up the density changes, so a litre injected means less than a litre is taken from the fuel tank, but this is a pretty small error.

The Disco3.co.uk website has some thread about how there is no longer a "low fuel" light on the dash (since the fuel guage is part of a tv screen). Instead when fuel gets low, the engine performance decreases to eke out the remaining fuel and (if my memory is correct) shut it down before the final fuel is consumed to protect the emissions and injector systems. A faulty tank sensor reading 0% would cause this. That may be why there are 2 sensors to provide redundancy. If this is indeed the case, then the computer takes the lowest setting, so it's "fail off", which may not be all that great out bush....

[Graeme]

There is a low fuel warning as I had it once. IIRC there's an amber bowser symbol, an amber triangle and a message that keeps being presented and the fuel consumption etc display changes to the distance to empty display.

[wombathole]

Gday,
Its been two years since this fuel drama with my brand new D4. Once the root cause was found, i've had absolutely NO issues with the vehicle since. The issue was... a petrol cap was installed on my diesel vehicle!

Petrol cap is a sealed unit, so no explosive vapour gets out. The Diesel cap has a valve to equalise the pressure in the tank. With the wrong cap installed at the factory, my tank was a sealed volume, the pump would suck out the fuel and create a vacuum. After about 300km, the tank was sucked in like a prune and pump couldn't suck anymore. The crinkled tank bent the sensors all around and caused the computer to totally get confused. The common rail would be starved and computer would kill the engine instead of letting a diesel run out of fuel.

Such a simple root cause to a total killer of a problem!

Land Rover agreed to replace the entire tank, all sensors, fuel pump and lines right up the common rail, and of course put on a bright yellow diesel cap. :) They said they have not seen the issue anywhere before.

I suggested that for such a possible thing to happen, they really should have a thread or keying mechanism on the fuel caps, so a diesel and petrol cap wont fit each other. Does anyone know if the newer D4's fuel cap has been redesigned???

End of story. :)

[Graeme]

Many years ago I had a BMW Isetta that temporarily had the same type of problem when the breather hole in the cap got blocked.

Its good to know that a petrol cap is not a substitute.