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MG MGF Technical - CO/lambda

As I predicted last year my F has failed on emissions, with a fast idle CO of 0.8 HC69 and lambda 1.006. I was told by mechanic that cleaning the lambda sensor in petrol sometimes helps. Also the downpipe is very slightly leaky so maybe this is affecting emissions? I will try changing the rather elderly spark plugs, and check the lambda sensor wiring. Any other ideas? Is it unlikely to be a faulty sensor with a normal lambda? I am not sure if I need to go to the expense of new downpipe or even new cat? I also remember a thread about using alcohol mixture to pass the MOT - is this possible/easily available.
How much will dealer testbook cost if that doesn't work?
Also the rear disks are badly corroded despite being replaced about 6 months ago - could this be faulty rear callipers?
Nathan Carnie

Hi Nathan,

on my VVC I got CO (idle ) 0,5 , HC 099 , CO (at 2500 rev/min.) 0,3 and Lambda 1,02. This was all more or less spot on maximum value ! As You are so close to pass test to nearly empty the tank and fill at least 0,5 L of carburator alcohol. This will get You thru at the CO - test :). Immediatly after the test fill up with petrol as usual. I have found that the cat on the "F" really needs to be at temperature to work at itīs best. So a quick coldstart at the MoT will NOT give correct values.... At least 5 min . fast idle OR direct from a normal drive will give better readings.

Regards , Carl.

í really serious with this question. Where is the lambda sensor located & how does it look like?

Regards on any info/pics.

You mention brake disc corrosion - do you mean rust ?

Or grooves ??

what pads are you using ? some sintered pads can cause problems with discs - ie rust - pitting

Six months to wear out discs !!!- there is a definate problem - take it back to the place that replaced discs and tell them to sort it for free!

Passing co test - - check for clean unblocked air filter - plugs is a definate - if 18i change dizzy cap etc - unless its been done recently - then as messages before - you can also have the fuel air mix tweaked i believe - by using a resistor in line ! - well we did it on the bikes :)

>Where is the lambda sensor located & how does it look like?

Exchaust manifold lower end, just above the flange.
Hard to get I out, from what same wrote here the other day.
The cable is covered by a silver coloured hose.
See between manifold and engine block.

Dieter &
Dieter Koennecke

Tony- the disc has gone rusty and is pitted mainly on outer edge, presumably from poor pressure from the pads (ferodo) I would love to tke it back to the place that fitted them - unfotunately I fitted them myself. The garage said braking test passed, so they will pass it if I wire brush the rust off! Better than spending 80 quid on a new pair of discs, but I suppose I really need new calipers.
I think the sensor is fitted to the downpipe near the manifold connection. If anybody has a picture it would be useful. Has anybody removed one on a 6yr old car -- will it be welded together?
Where can i get carburetor alcohol in the uk, Can i use cheap vodka or will it blow up my engine?
The K&N isn't blocked - i would expect it would reduce rather than increase CO compared to standard?
Nathan Carnie

Thanks for the picture Dieter but can you describe where the sensor is as I'm not sure I can see it.
Nathan Carnie

Be careful removing the Lamda sensor, mine broke in the manifold and cost Rover and me a new manifold

It may not be welded together: in theory ( :-) ) they should have used a "special" goo to mount it that has glass beads in it, which will enable removal at a future stage.

If you DO fit a new one (they're quite cheap I gather - our Astra has one that sometimes reports a fault on the ECU, and I'm sure its on the way out: it got anti-freeze in the exhaust due to a HGF), make sure you fit it with the right stuff: the new one may well come with a sachet of it.

Other times, they're pigs to get out!

I'd try the new plugs and clean air filter route first, I think...

Good luck...


Hi all,
if of interest I can supply how to check the lambda-sonde in situ with a digital voltmeter. Not difficult but needs SOME DIY-knowledge....

Regards , Carl.

please supply :)
Good stuff for the site and the archive in any way.

I'm sorry, but I've got no better picture currently. The sensor is behind the lower end of the manifold, though.

Please notice as well that the sensor needs NOT to be bought from original MGR ! It's a standard part which should be availiable also from different car parts shops. I can't recall exactly, but it may be from Bosch cheaper ?

Dieter Koennecke

I feel yet another warranty claim coming on - I'm well known to the warranty company who could soon be going out of business.
Nathan Carnie

Well then , here we go : Among all the multicoloured cables entering the MEMS unit there are for the 1.8 I as well as for the VVC one solid grey and one light-green with a grey stripe. These are the 2 cables from sensor part of lambda sonde. Measuring over these 2 cables with a digital voltmeter, (2 Volt range or whatever close on Your meter )will on a healthy lambdasonde give heavily fluctating readings between almost 0 Volts and around 1,3 Volts maximum. This should be measured after warmup at idle. A partly faulty unit will show a more or less steady reading within the range of 0 to 1,3 Volts or never reach beyond something like 0,5 - 0,8 Volts.. Heavy rapid changes is the good thing to look for. As the digital instrument doesnīt update itīs readings as frequent as the sonde changes itīs voltage the readings will be erractic but this is NOT a sign of a faulty lambda sonde ! The corresponding 2 cables for the measurement can as on my car be fitted with a small mating contact for future readings. Do not use too long unscreened cables (several meters long) as there is a possible pickup of inteference that can interfere with the readings and work of MEMS.

Regards , Carl.
PS. Dieter, is "" full or have You got latest pict. of hydragas + external thermostat ? Notice if I have to re-send it !



If you are getting pitting on the disc faces it will be the sinter in the pads - It is not poor quality discs!

The sinter encourages rusting - In fact the pads can rust solid to the discs in one night ! Trust me I have had this happen ! No not on the car but on a bike - In fact a very common problem with certain combinations of pads and discs!

Ferrodo pads probably have a high sintered metal content which is basically a rust factory!

The answer - change to EBC HH pads - They will also clean up your discs !

Its nothing to do with your calipers - if your experiencing poor braking the caliper pistons may need a clean up from all the oxide build up due to the fist problem!

This thread was discussed between 07/11/2001 and 08/11/2001

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