Thread: LR3 2006 4.4ltr, fuel issues which Land Rover cannot diagnose

Originally Posted by the_preacher1973

I believe he's thinking that if they're using an absolute pressure gauge it may be adding in the 15 psi of normal atmospheric pressure so you get 65 +15 = 80 which means it is actually within spec and this is a red herring.

Ahhhh! Understood. I don't know -- but I will find out Monday.

Update!

Fitting a new MAF did not resolve any of the faults.

But I think I have found the problem. I launched all items in the code reader, and went through them one-by-one when the problems were absent as well as when the problems were manifest. The main distinction is that when the vehicle starts to run poorly, the Engine Output 1 - Fuel cut off was ON This explains all of the faults.

When I cycled the key, the vehicle started, but the fuel cut-off hesitated between ON/OFF (flickered between 'ON' and 'OFF') a few times and then stayed 'OFF', and the vehicle ran perfectly. Concordant with the fuel cut off being 'OFF' was a strong pump sound heard through the filler cap -- when the cut off was 'ON' the pump was noticeably quieter and seemed to be struggling.

The fuel cut off does not seem to be complete, but I am unfamiliar with how the ECM controls the cut off and by what mechanism it does it. There is a strong correlation with Ambient air temperature, or fuel temperature -- what can affect fuel cut off that is temperature related?

The Engine Output 1 - Fuel Relay is permanently 'OFF' and is throughout the testing -- either when the vehicle runs well or runs rough. I would have thought this should be 'ON' when the vehicle is running. I also heard the E-box fan running when the code reader clearly shows it as being 'OFF'.

It seems to me that the fuel cut off seems to develop a partial feed to partially activate it -- any suggestions?

Can someone please provide me with the locations of the grounds that the ECM uses for switching (especially for anything it grounds relating to the fuel system). I have read the document that was kindly provided -- but it does not mention anything about fuel cut off. (I am assuming there is nothing obvious like an old Ford-style inertia cut of valve that might have become wet?)

I should finally point out that with the vehicle running, removing the fuel relay causes the vehicle to stall shortly afterwards, so the fuel relay is working. I have also switched it for another relay of same type to check the relay itself.

some great differential diagnosis.
keep the updates coming.

Can you check to see if the fuel tank pressure sensor functions properly too? That will have an affect on how your ECU determines fuelling.

Originally Posted by banarcus

Can you check to see if the fuel tank pressure sensor functions properly too? That will have an affect on how your ECU determines fuelling.

Thank you for the guidance. I can check the operation of the fuel pressure sensor, but I am not certain that there is one inside my tank. The wiring schematic I have for the tank shows no pressure sensor (I was taken to understand that the pressure regulation was a mechanical on the pump itself and was not monitored electronically).

Do you know where in the tank this would be? I am assuming that any data it provides must come out of the multi-electrical plug on the top of the tank?

I have been told that Land Rover observes:

"If there is a process fault in the ECM, the ECM either uses fuel injection cut-off to limit engine speed to 1300 rev/ min or disables fuel injection*to stop the engine."

This sounds like it might be the issue. I find it hard to believe that there has been an ECM fault, and much more likely to be some sensor or transistor breaking down under heat as the correlation between the ambient air temperature and the symptoms is clear.

Would anyone consider a dodgy ground to/from the ECM to be a potential issue?

When I did the Green Oval Experience seminar Gordon mentioned 3 electrical connections that cause issues when they get wet.From memory,the gearbox/transfecase ECU under the bonnet,wich you said is ok.The others were near the air susp compressor and above one of the rear struts near the fuel tank.He reccomended electrical sealant to be used in these areas.Worth checking/cleaning.
Andrew

Ok, here's the deal. The symptoms are generated by the ECM output 'fuel cut off' which flickers ON and OFF, then eventually stays ON.

[B]Apart[B] from the ECM, what could cause tris issue -- especially one which is temperature related (though the flickering happens at start up for a couple of seconds and then settles down). I'm thinking its a grounding issue.....