emissions failed mot???

falling-out-with-my-car · Post by **falling-out-with-my-car** » 14 Apr 2009, 23:38

Hi, we have an M reg citroen AX that was last on the road three months ago, it is now on a sorn so we cannot ideally drive it on the road to give the engine a good blast out before its MOT test because of this it has failed its emissions test today.

Now appart from the obvious things like cleanning the plugs, new airfilter, oil change etc are there any tricks worth noting? with my diesel I usually fill the filter chamber with diesel injector cleaner and drive the car hard to blow the soot out of the engine.

is it worth putting redex through the carb intake on the AX? any ideas please, would be gratefully recieved

regards Nigel.

Post by **CitroJim** » 15 Apr 2009, 05:52

How did it fail Nigel?

Do you have the print-out from the emissions tester for us to look at as it'll help enormously.

citronut · Post by **citronut** » 15 Apr 2009, 08:16

how far was the car driven to the MOT station, because you cant get a fair emmisions result if the engine is not hot, also if the car when last used was only ever tooodald round town it will definatly need a good blast 2 or three times for a few seconds ern route to the test station,

if you cant drive it far to the test station just get it hot whilst its parked then on the way to the MOT give it a blast flat out in second gear 2 to 3 times

i never use any addatives before taking my own or custamers cars for a MOT, just the MEXICAN tune up method and very seldom get an emmisions fail on diesels

regards malcolm

fred1 · Post by **fred1** » 15 Apr 2009, 09:00

Hi,

You need to look at what aspect of the emission test it failed.

If your is a petrol injection model there may be a problem with the lambda probe failing.

This measure the oxygen content in the exhaust gasses and adjusts the fuelling ratio accordingly. It often fails so as to over fuel and give rise to very high hydocarbon (HC) readings. If so this will be clear on the MOT print out.

The lambda probe screws into the pipe just below the manifold, however, they often seize in and in the past I have had the mounting boss detach from the exhaust when trying yo unscrew, resulting in a new front pipe !!

In fact many replacement front pipe for the AX come with a seconf !spare" boss with a plug in it!!

Regards

John

falling-out-with-my-car · Post by **falling-out-with-my-car** » 15 Apr 2009, 11:36

fast Idle test:/ Min Limit. / Max Limit. / Actualvalue: /Pass/fail.

Rpm/ 1/min:/ 1950/ 2550. /--------- /Not chKd.

Co/ %Vol:/ ---------/ 0.300. /0.482. /fail.

HC / ppm Vol -------/ 200. /113. /pass

Lambada:/ : 0.970/ 1.030. /1.027. /pass.

second fast idle test.

Rpm 1/min / 1950/ 2550/ --------- /Not checked.

Co %vol. /------ / 0.300/ 0.443. /fail.

HC ppmVol /--------/ 200/ 120/ pass.

Lambada : / 0.970/ 1.030/ 1.020/ pass.

Natural Idle test.

RPM 1/min /750 /950 /--------- /Not checked.

CO %/Vol /------ /0.500. /0.171. /pass.

Overall Result: Exaust Emissions test. /Fail.

unfortuynately the info wont stay in the form i typed it in in colums left to right.

Hopefully you can help by decifering what the problem might be please Jim.

by the way it is a petrol 949 cc citroen AX with a catalytic converter.

thanks in advance Nigel.

red_dwarfers · Post by **red_dwarfers** » 15 Apr 2009, 12:02

citronut wrote: i never use any addatives before taking my own or custamers cars for a MOT, just the MEXICAN tune up method and very seldom get an emmisions fail on diesels

regards malcolm

Thats a point, when I tool my Xant to its MoT, they didn't test for emmissions

Im not complaining but that can't be right?

Post by **CitroJim** » 15 Apr 2009, 16:46

Hi Nigel,

Your basic problem is high HCs resulting from a slightly lean mixture. This is denoted by the lambda value being just above unity.

It looks like your lambda (oxygen sensor) is OK as the ECU appears to be running Ok in closed-loop and controlling the mixture as well as it can.

High HC readings, although in spec. mean less then perfect combustion and this may be down to plugs, bad valve clearances (leaky valves can cause it too) or air leaks on the inlet manifold upsetting the MAP sensor. In fact, the pipe between the inlet manifold and map sensor may well be the problem as they often perish and let in air.

Also, give the crankcase breather arrangement a good clean up, as well as the throttle body. Then check the air filter is nice and clean and all should be hunky-dory.

My money is on a perished pipe causing an air leak. Hope that helps Nigel.

Kev, diesels are a much easier prospect at MOT time. Only smoke density is checked and if they don't smoke on the snap accelleration test, they'll pass

falling-out-with-my-car · Post by **falling-out-with-my-car** » 15 Apr 2009, 17:51

Thank you for that Jim,

I will have a look at it tommorrow, I have been stripping down the front of the GSA ready to pull the engine to fit new crankcase seals.
we had to stop at the 42mm nut which holds the fan on.
found a socket though in a local tool shop £27.00.

Right at least you understood the emmissions results thank god, the forum made such a mess of my neat layout, when it was posted.

fortunately I now know what a map sensor looks like after trying to find one for a friends Peugeot on a scrap yard.but I have never seen one on this AX as yet. It must be hiding behind the engine somewhere.

I will check the hose as instructed tommorrow, change the oil, renew plugs and air filter and see how we go.

thank you once again for all of your help today in all techy departments.

regards. Nigel.

falling-out-with-my-car · Post by **falling-out-with-my-car** » 15 Apr 2009, 17:56

Kev,

just because you haven't got the emmissions result on paper doesn't mean it wasn't tested, sometimes if yor car passes the tester doesn't pass on the paperwork, but if it fails you ussually get the paperwork esspecially if it fails on emissions.

most people are just overjoyed that their car passed its MOT and forget to ask for the emmissions slip if it has been forgotten.

The Mexican tune up as you call it, Malcom,
can damage your diesel engine, so a citroen mechanic once told me, thats why I always knock back my throttle cable a couple of notches before the test on the xantia

there is a split pin on the cable outer near to the injector pump which has slack adjustment rings in it pull the pin and let the throttle cable loosen off a couple of notches this stops your engine and more importantly your turbo being damaged during the MOT test.
if the engine is turned off above idle speed turbo damage can result I think you will find a warnning about it in your manual.
so lowering the upper throttle limit a little should offer some protection allowing the throttle to return to idle a little quicker than normal.

you can always adjust it back up again after the test. if you stopped and listened to how hard the diesel engine is reved by the tester you would wonder why it doesnt do any damage being reved so hard. why they do this is beyond me as most diesels if driven properly hardly ever enter the red on the rev counter whilst being driven on the road unlike petrols driven by petrolheads or boy/girl racers.

regards Nigel.

MikeT · Post by **MikeT** » 15 Apr 2009, 18:18

Hi Nigel,

Don't forget the good advice earlier - on the way to the test centre, give the car a good thrashing to get it hot - heatsoaked hot is best - and when you pull into the MOT shop minutes before it's due, don't turn the engine off, then ask they test the emissions first. Might be worthwhile pre-arranging this with them.

Additionally, a good service - especially an oil change - will collectively improve the emissions.

Good luck!

falling-out-with-my-car · Post by **falling-out-with-my-car** » 15 Apr 2009, 18:22

thanks for your advice everyone I think Mike T has in in a nutshell

LUCK, thats what I need...........lol.

Post by **myglaren** » 15 Apr 2009, 18:46

My Accord was failing the emissions test one time and the TESTER took it out for a ten mile blast down the motorway and retested it as soon as he got back - passed of course

citronut · Post by **citronut** » 15 Apr 2009, 19:11

firstly Nigel sorry i just re/read your first post saying this is a petrol AX,

secondly when you floor a diesel in second gear it will not over rev as there is a limiter in the pump, when i do this it feels like the car is beeing held back when it is flat out, and it also dose not go anywhere near the red

on your read out it shows the labada is very close to the limit,
it might help to take it out and clean it with carb cleaner

regards malcolm

_kid_ · Post by **_kid_** » 15 Apr 2009, 19:43

the fast idle result is only just a failure. the car (esp as sat for 3 months) may simply need a good blast. your lambda sensor seems ok. check you plugs, air filter and oil, if any look dirty change otherwise they may not make too much difference. as said previous air leaks are a possibility.

falling-out-with-my-car · Post by **falling-out-with-my-car** » 15 Apr 2009, 20:09

new plugs, oil and air filters tommorrow and a check of the pipes for cracking and we shall send it back to the MOT station before we have to pay another £50.00 for another test.
we will give it a good blast in second gear before then test several times making sure the engine is nice and hot Im not to sure about attempting to remove the lambada sensor without breaking the mounting it sits in on the down pipe the results show that the lambada passed i gather. so we shall just have to hope the rest does it.

thanks again everyone. regards nigel.

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emissions failed mot???

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