failed MOT

[jdearden]

right no surprises failed mot on emmisions.
the readings were as follows
co2 fast idle 1.12%
lambda fast idle 1.02
it is failing on the fast idle. Im only running one cat but this is higher than it should be. any ideas gus.
the car is running rich which will be sorted by yellowshed when i can get it to him. anoy1 got any tricks that may get this down enough.

[worty]

If its got an MBE ECU could be the front lambda. Mine tends to eat them on a fairly regular basis.
Can you plug it in to a laptop and see what its doing?

Might be a simple change of lambda and reset the adaptive map and bobs your uncle

worty

[jdearden]

well ive just cleaned the sensors and put a bottle of cleaner in the engine run the tank down will go drive like i stole it for 30 mins and put it into the garage to be tested while very hot and hopefully will sort it, if not off to see a friend of a friend of a friend

[jdearden]

right still failed but better checked the front lamda and it is up and down like a yoyo so needs replacing. where do i get one from. is it a ford part

[hoyin]

When I had my problem - Plans got the prices for a replacement for me.

They were not that cheap. However in the end I did not need it, the sensor was just unplugged!

Plugged it back in drove it for a couple of hours and took it down to my local cheap MOT place and it was fine.

[JLSELAN]

jdearden said:

well ive just cleaned the sensors and put a bottle of cleaner in the engine run the tank down will go drive like i stole it for 30 mins and put it into the garage to be tested while very hot and hopefully will sort it, if not off to see a friend of a friend of a friend

AFAIK Lambda sensors cannot be "cleaned" -- they have a special (and fragile) surface coating that will be damaged in any kind of cleaning process. Replacement is really the only option.

[YellowShed]

jdearden said:

checked the front lamda and it is up and down like a yoyo so needs replacing.

For those that don't know, the Lambda sensors are supposed to go up and down!! They should range from 0-1V on the signal cycling about once a second. They're faulty if they don't go up and down - i.e. usually stuck at 0V

YellowShed

[worty]

From the wiki

Lambda sensors
Part numbers
1001702, 96889F472BA , SENSOR ASSY C85432, D4 (WP)
Available from Ford.

I think the 88 in the second number should be BB. There about £60

Yellowshed has probably forgotten more than I will ever know about these things but it should move up and down. Check the range against the rear lambda (MBE only) should be similar. If you take the Lambda sensor out give it a shake and see if it rattles (make sure you hold the buit in washer) if it does its dead. If it doesnt could still be ok.

worty

[YellowShed]

jdearden said:

co2 fast idle 1.12%
lambda fast idle 1.02

Lambda greater than 1 and high CO (not CO2) means you have an air leak upstream of the lambda sensor. Find and fix air leaks - possibly both banks and you should be set.

YellowShed

[andygtt]

is it possible to pass an MoT with a decat exhaust?

I've got 2 and considering converting 1 to a decat pipe as the cats wee knackered.

[Gadgeroonie]

no unless you know the mot tester very well !

[brischi]

hello guys sorry for the small British ......... and possible cracked exhaust manifold, oxygen sensor does go off the machine sobs, tears, it blows the 3000 and 4000 RPM?? I'm going crazy ...... 2 new Lambda sensors !!..... thanks ...... tnanks

[brischi]

Noble scan with the program only works with a probe 4/5/6 front bench work bench ....... back after 1/2/3, minutes far exceeds the value 1 and stops ........ manifold cracked. ....3000/4000 sobbing my noble....

Edited by brischi on Thursday 17th June 15:50

[brischi]

YellowShed said:

jdearden said:

co2 fast idle 1.12%
lambda fast idle 1.02

Lambda greater than 1 and high CO (not CO2) means you have an air leak upstream of the lambda sensor. Find and fix air leaks - possibly both banks and you should be set.

YellowShed

Noble scan with the program only works with a probe 4/5/6 front bench work bench ....... back after 1/2/3 minutes far exceeds the value 1 and stops ........ manifold cracked. ....3000/4000 sobbing tha noble ........spark plugs, cables candles, reel, westegate, APS .... brand new ....

Edited by brischi on Thursday 17th June 15:48

Edited by brischi on Thursday 17th June 15:53

[jdearden]

YellowShed said:

jdearden said:

co2 fast idle 1.12%
lambda fast idle 1.02

Lambda greater than 1 and high CO (not CO2) means you have an air leak upstream of the lambda sensor. Find and fix air leaks - possibly both banks and you should be set.

YellowShed

the manifold were blowing but they are sorted now. where else could it be blowing as lamda sensors are in the manifold.

[BobE]

YellowShed said:

jdearden said:

co2 fast idle 1.12%
lambda fast idle 1.02

Lambda greater than 1 and high CO (not CO2) means you have an air leak upstream of the lambda sensor. Find and fix air leaks - possibly both banks and you should be set.

YellowShed

I`m trying to understand the logic here - I know Trevor is the expert but doesn`t a high CO value mean the mixture is too rich? (There is insufficient oxygen to turn the CO to CO2 as there is too much fuel in the mixture). Also the exhaust gasses are above atmospheric pressure so exhaust gasses can leak out but no air/oxygen can enter the system - and so an exhaust leak shouldn`t change the composition of what remains and is being `measured` by the sensor?

[YellowShed]

BobE said:

I`m trying to understand the logic here - I know Trevor is the expert but doesn`t a high CO value mean the mixture is too rich? (There is insufficient oxygen to turn the CO to CO2 as there is too much fuel in the mixture). Also the exhaust gasses are above atmospheric pressure so exhaust gasses can leak out but no air/oxygen can enter the system - and so an exhaust leak shouldn`t change the composition of what remains and is being `measured` by the sensor?

Ok BobE - emissions 101. Firstly, at idle and fast idle, the exhaust gases are highly pulsed and will definitely have periods of below-atmospheric pressure - thus air (and consequently oxygen) will get into the exhaust stream. Such an air leak upstream of the sensor will be seen by the sensor as a lean mixture. It will then richen up the engine fuelling. This will give the high engine-out CO. Because the air/oxygen doesn't fully mix with the exhaust, the cat can't use that oxygen up to reduce the CO, nett result is that the oxygen and the CO come out the tailpipe. The gas analysers used for measuring exhaust lambda see the oxygen as a lean mixture yet the CO is still high. Hence the high CO readings yet lambda is lean (1.02).

A dying cat scenario would give both high CO and hydrocarbons, and I'm assuming the HC reading was within spec? as it hasn't been mentioned.

YellowShed

[BobE]

YellowShed said:

BobE said:

I`m trying to understand the logic here - I know Trevor is the expert but doesn`t a high CO value mean the mixture is too rich? (There is insufficient oxygen to turn the CO to CO2 as there is too much fuel in the mixture). Also the exhaust gasses are above atmospheric pressure so exhaust gasses can leak out but no air/oxygen can enter the system - and so an exhaust leak shouldn`t change the composition of what remains and is being `measured` by the sensor?

Ok BobE - emissions 101. Firstly, at idle and fast idle, the exhaust gases are highly pulsed and will definitely have periods of below-atmospheric pressure - thus air (and consequently oxygen) will get into the exhaust stream. Such an air leak upstream of the sensor will be seen by the sensor as a lean mixture. It will then richen up the engine fuelling. This will give the high engine-out CO. Because the air/oxygen doesn't fully mix with the exhaust, the cat can't use that oxygen up to reduce the CO, nett result is that the oxygen and the CO come out the tailpipe. The gas analysers used for measuring exhaust lambda see the oxygen as a lean mixture yet the CO is still high. Hence the high CO readings yet lambda is lean (1.02).

A dying cat scenario would give both high CO and hydrocarbons, and I'm assuming the HC reading was within spec? as it hasn't been mentioned.

YellowShed

Thanks - I can understand the scenario if the exhaust manifold pressure can go below atmospheric. I guess that`s possible as I recall certain two stroke motorcycle engines had their exhausts tuned to pull through the induction system with overlapping valve openings. (The exhaust pulse created a vacuum that pulled through more fuel/air than would normally happen - a sort of vacuum forced induction if that`s not a contradiction in terms).

[jdearden]

well good news she will be put through her mot on monday with no problems. just need to get her to you trevor to sort my map out and stop it running so rich.