Poor MPG

[philr]

Anybody got any ideas on why my MPG might have dropped significantly over the last year on my 97 5.0l Chimaera ?

I'm not aware of driving with a heavier right foot or anything, but on my shortish comutes to work + around , I used to get 17 to 18 MPG, but now I am only getting 14 or 15 at a push !

On long cruising runs I seem to still get 23 to 24 MPG which is the best I have ever managed.

I was wondering if there was a fuel leak somewhere possibly, and whether there were any usual places that Chimaeras have fuel leaks.

[philr]

Finally got round to getting this checked by Fernies today. Instruments confirmed that both banks are running rich. Fuel presure checked and OK, so apparently this does indicate that the Lamda sensors are not behaving themselves. Do these break down over time ? The car has approx 44k on the clock now.

Estimated cost is £150 per Lamda sensor. Ouch !
Is the replacement of these sensors something that is easy to do, or best left to Fernies.
Is there a recommended place to acquire new sensors from in the safe knowledge that they are the right ones ?
I thought I'd heard that a special tool was needed to remove/fit the sensor.

[philr]

They plugged in a sizable hand held reader. Bigger than the basic fault code readers that Ive seen used before. This came up with much more detail than the fault code readers I've seen used, actual values and scales etc.
The value for one of the readings (for each Lamda sensor) was given as "RICH".

[philr]

I believe that it was £150 per part.
I did see at www.gendandirect.co.uk/viewcategory.php?category=111
that the ones for a landrover were more like £90...but which one I wonder. Are thse the correct ones to go for, are there better ones to go for ....

Where is the Cold Start Sensor located + how much should I expect to pay for one + is is easy enough to replace ?

[philr]

poorpeet said:

Given the cost I'd be inclined to replace the temp sender before the lambda sensors just incase

Poorpeet,
Where is the temp sensor ?
Do you know the part No or where best to get this from, and ofcourse the approx cost.

[philr]

Mine runs about the same, though the under bonnet temp has always been higher than I felt it should be.
I understand where you are coming from with this, but I don't believe that this is the case for me.

[philr]

bought the replacement lambda sensors (< £80 each for genuite NGK parts).
Bought the socket (17mm deep), bought the angle grinder, cut slot into side.
Modified socket is a perfect fit and did the job well.
Reset the ECU.
New sensor seems to be working well.
Engine seems to run much smoother than before, even on cold start.
Need to see if the MPG improves now.....

All told cheaper than £300 + 1 hours labour to fit.

Note that with reading up on the Lambda sensor, it seems that they should be regarded as consumables in the same way as spark plugs. Life expectancy is around 30,000 miles. So at 44k mine were due a change.

Thanks for everyone's input and advice.

[philr]

Hmmm.

1st refill after the change of Lambda sensors and I'm getting 14.5 MPG only. Not the 18 that I was hoping to get back to, but slightly better than 12 to 13 that I was getting.

Lets hope things start to improve further from here.