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.

[kevin Secker]

My '97 Chimp has done exactly the same thing only it happened two years ago. I have had everything that is sensible to check checked and it cruises it's MOT. Mine's done 33000 miles. I believe the cam is OK but it could be that or it could be injectors.

If you find out please can you let me know.

Cheers
Kevin

[Bob the Planner]

When the lambda sensors on the tuscan failed my mpg dropped significantly - I assume that the ecu went into limp home mode. I don't know if its the same for Chims though. Could also be a water temperature sensor

If its running rich you mauy notice more burble however it will not be doing the cats any good.

I may be way off the mark with the above.

Bob

[greenv8s]

I would suspect it is running rich. Potentially caused by a sensor fault or an exhaust leak.

[Ribol]

I would have thought that the fact that the economy is correct on long runs but worse on short ones might point to a cold start sensor problem. Possibly running rich for longer than necessary starting from cold?

Ivan

[greenv8s]

Good point. If the stat was leaking it would take longer to warm up?

[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.

[Big Al.]

philr said:

special tool was needed to remove/fit the sensor.

Calling DustyC




Sorry can't help on this occasion.

[wildeep]

Faulty temperature sensor can also cause it to run rich. Its a lot cheaper than a new lambda sensor. Did they check that it was the lambdas using a fault code reader or just guess?

>> Edited by wildeep on Monday 25th October 17:41

[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".

[poorpeet]

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

[chimtvr]

lambda or o2 sensors have a heater circuit in them and they only work when they are very hot so... if the heater element has gone they wont get hot quickly.
when you go on a short journey they wont reach temperature so therefore will give a false reading
When you go on a long journey eventually the exhaust gases will bring the sensor up to temperature and so it will work you can test the sensor using a volt meter and its just a landrover discovery sensor nothing special if you want i will check what type of sensor and then can tell you what voltage readings you should get
Dave

>> Edited by chimtvr on Monday 25th October 19:48

[ian8542]

philr said:

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.

You could quite easily alter a deep 3/8" drive socket to remove the sensors, or you can buy the real mcoy from Snap-on.
The sensor wiring is ty-wrapped to the chassis and plugs into the loom. Fairly easy replacement.
As previously mentioned a faulty CTS will cause rich running and has been known to occur.
Check that the air filter is clean too.

>> Edited by ian8542 on Monday 25th October 20:14

[joospeed]

you sure they don't mean 150 pounds the pair??

they're bleeding expensive sensors, and more than you'd pay at a dealer .. the ones i use are half that pirce ..

[jtong]

I'm watching this thread since my MPG is also higher than usual (current 16MPG instead of 19MPG). The Chim has recently passed its MOT so could it still be running 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 ?

[chimtvr]

Ok i decided to check as long as yours is the same as mine have a look for yourself to be sure they should have three wires coming out of them one white one black and one red
This is a landrover part out of a 93/94 3.9 discovery its a 3 wire zirconia sensor part number ERR 6729 available online from www.land-rover-parts-shop.com for 87.15 hope this helps
Dave

[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.

[david beer]

What temps are you seeing, i know of someone who had a very early opening water stat that meant it ran with the "choke on", i know its not a "choke" but you know what i mean ! It would only become noticable in the cold weather, mine runs at a comfy 88, winter or summer.

[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.