TD5 Auto fuel issue

Hi all, I recently bought a very nice 02 TD5 auto, with a years LR warranty. It has been back to the dealer twice so far for little faults (intermittent cruise control, suspension switch on dash not working etc).
I pursuaded them to fill her up with fuel on collection, & have been keeping her topped up ever since, checking consumption each time, for the first week or so she was returning 27 overall, which I was quite happy with, but suddenly it has dropped dramatically to about 17 (sometimes less). The dealer plugged her into their magic "Test Book" and can find nothing wrong.
What I want to know is, can I insist that they sort this out under the warranty, to me its obviously a major fault with the engine management system or whatever.

Td5 auto is not the best on fuel anyway and I'm surprised you were getting 27mpg overall, town driving is very poor and 17 or less is about right.

If your dealer can't find anything wrong then there's no point pestering them as they'll come back with the same verdict every time and you'll just inconvenience yourself and get wound up, you can try though, first thing you can do is get them to check the air flow readings and get a printout to give to you, readings should be 90kg/hr @ idle and 350kg/hr @ 3000 rpm if thats ok then obvious things like a fuel leak should be checked, if all that checks out ok then there is not alot they can do.

The computer interface on the TD5 is not "all-knowing" and will actually spot very few faults. For example it does not 'know' either the fuel pressure or the boost pressure. It does know ambient temperatures (which you know anyway) and fuel temperature.

And many of the faults that the ECU logs are either impossible (stuff to do with the EGR where there are no sensors) or ridiculous (complaints about the auto box when the car is a manual).

It will spot an injector that does not work at all, but not one that does not work very well.

About the only thing it always gets right is Air Flow Meter failure, though sometimes that can be fixed by a squirt of WD40.

And it will often spot that the engine has 'overheated' with the result that the aircon fans are permanently on until the fault is reset.

And sometimes it will shut down the engine for no apparent reason at all

So don't expect any miracles...

JimAttrill said:

The computer interface on the TD5 is not "all-knowing" and will actually spot very few faults. For example it does not 'know' either the fuel pressure or the boost pressure. It does know ambient temperatures (which you know anyway) and fuel temperature.

And many of the faults that the ECU logs are either impossible (stuff to do with the EGR where there are no sensors) or ridiculous (complaints about the auto box when the car is a manual).

It will spot an injector that does not work at all, but not one that does not work very well.

About the only thing it always gets right is Air Flow Meter failure, though sometimes that can be fixed by a squirt of WD40.

And it will often spot that the engine has 'overheated' with the result that the aircon fans are permanently on until the fault is reset.

And sometimes it will shut down the engine for no apparent reason at all

So don't expect any miracles...

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Are you using Testbook or Rovacom/autologic ? Reason I ask is because Testbook does monitor Boost pressure and once you get used to it its a very good aid to faultfinding.Even the fault codes are fairly accurate if you know what you are looking at.My only frustration with the TD5 is that the engine Ecu does not monitor rail pressure - so Testbook can not show it either.
If you look at the diagnostic kit that some OEM's supply then Testbook is up with the best.I was one of the first independents to buy it back in 2003,and apart from 2 screws missing from inside the Dell laptop,(which stopped the screen working properly a month ago) it has worked faultlessly.I often get called to other local independents when their other kit wont work or give false info.
Sorry to bang on but I have earnt a good living with it,and I am fed up with people moaning about it,esp as the aftermarket manufacturers keep on how c-ap it is when half the time their kit doesnt even cover all the LR variants.
As for the fuel consumption,Clutchdust is right,but even when the AFM outputs get ignored and the Ecu runs in default,(unfortunately quite common) fuel consumption doesnt seem to get much worse.Or complaints of black smoke on acceleration.Customers of mine usually admit to 20 - 24 mpg, so 27 is probably a bit optomistic - are you sure the tank was actually brimming when you refilled it ?

You are right. The ECU does know the boost pressure. It's just a pity it doesn't know the fuel pressure as a lot of faults are either the pump or the pressure regulator.

JimAttrill said:

It's just a pity it doesn't know the fuel pressure as a lot of faults are either the pump or the pressure regulator.

Click to expand...

It doesn't really need to, if it don't start and logs no faults then fuel delivery is the first place I'd look for a fault. even when the pipe near the tank has chaffed through and ****ing diesel everywhere (A169 recall) the engine still runs fine, so fuel pressure monitoring is not really that critical.