Lack of Power

sierrafery said:

Did you read post #5 ?

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Yes I did... Whats your point ?

My point is in that post. Are you sure that your pump is working well?

Pressure test done a few weeks ago and sat at 4 bar

sierrafery said:

My point is in that post. Are you sure that your pump is working well?

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I'm still at a total loss why you would think that low fuel pressure would throw a driver demand high fault. There is absolutely no correlation between fuel pressure and pedal position so why would the ECU link the two? It doesn't even know what the fuel pressure is!

Phanc60844 said:

I'm still at a total loss why you would think that low fuel pressure would throw a driver demand high fault.
There is absolutely no correlation between fuel pressure and pedal position so why would the ECU link the two? It doesn't even know what the fuel pressure is!

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Read again post #7... i didnt think about the reasons, i've seen this happenning myself and happened to others too but i know how a fault code protocol works and it's not very uncommon that an ECU to throw a wrong fault code if some conditions for it are met even if those conditions are not 100% spot on

Phanc60844 said:

Think the ECU wasn't expecting that level of boost at that throttle position so declared that either could be at fault.

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if you apply the same logic the ECU doesnt know the fuel pressure but it calculates the IQ which must have a result in rpm so if the fuel pressure is low the IQ will suffer so the rpm will be different than the ECU expects at a certain throttle position hence it declares a driver demand fault... i dont know the real reason... just remember that there are cases when it happens in reality.

https://www.aulro.com/afvb/discovery-2-a/112980-td5-driver-demand-error.html#post1329071

You may be correct SF. A quick search finds others have had demand faults pop up, for other issues.

In my opinion, driver demand issues are always triggered by the accelerator pedal (hence the fault description) but can involve any subsystem responsible to deliver the requested torque, be it injectors, inlet manifold pressure, air flow, turbo, fuel quantity, etc. In short, anything that will affect the intensity of the combustion will impact the downward force on the piston and therefore the torque at the crank and thus engine speed and power delivered by the stroke. So I think it is safe to conclude that this fault is registered when the engine speed does not align with the expected rpm curve as calculated by the ECU on the basis of the the driver's accelerator input and other parameters.

NPG said:

So I think it is safe to conclude that this fault is registered when the engine speed does not align with the expected rpm curve as calculated by the ECU on the basis of the the driver's accelerator input and other parameters

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Good deduction, IMO we can presume that when the fuel pressure is low that's what happens hence the driver demand fault codes stored with pump working only on LP