Author Topic: mot fail on emissions  (Read 1671 times)

DeadBoB

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mot fail on emissions
« on: May 21, 2021, 10:23:55 AM »
hi i just installed both sensors on my catalytic convertor as it failed emissions due to both sensors missing, So now installed (EML went out straight away) its not made much difference failed a second time, im now stumped as my garage are saying its the sensors at fault, i have no idea, any thoughts?

E27006

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Re: mot fail on emissions
« Reply #1 on: May 21, 2021, 02:04:21 PM »
I'm sure the forum can help, we need to know a few details.
The history of your car.
Why did your car not have the sensors in the exhaust?
Please advise  details of your car, model year, engine capacity.
Please let us have a few details about the sensors you installed, new or used,  part numbers,  price and source.
Have you installed the sensors in the correct positions, they are not interchangeable, they are quite different,  one measures flow , the other measures exhaust gas composition. did you remember to remove the protection  covers from the sensors before installing them?
The MoT test produces a paper printout giving the results of the emissions test,  do you have the printout, please post the figures on the printout, it may give the forum members  a few clues as to the problem and a solution.


Diagnose Dan for a Youtube video on sensors and how to tell if the sensors are working or faulty


« Last Edit: May 21, 2021, 07:34:08 PM by E27006 »

Westy36

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Re: mot fail on emissions
« Reply #2 on: May 21, 2021, 04:21:26 PM »
I do know that cats work best when very warm. Have you taken your car for a decent 'Italian Tune Up' (decent thrashing). Can do a car the world of good and get things working again if it has only been pottering about.

culzean

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Re: mot fail on emissions
« Reply #3 on: May 21, 2021, 06:51:43 PM »
I do know that cats work best when very warm. Have you taken your car for a decent 'Italian Tune Up' (decent thrashing). Can do a car the world of good and get things working again if it has only been pottering about.

Yeah, short journeys are bad news for CAT, need to get hot to work and low revs and short journeys just don't do it.  Just like DPF of Diesels would get blocked if never given a blast on motorway.  After a few weeks of short journeys you may notice an 'eggy' smell from CAT,  that is a sign it needs a decent journey ( 20 miles plus )  at decent revs, at least a semi-Italian tuneup.  Will also get oil 'proper hot' and boil out any water or acidic bits in there.  Short journeys can also result in choked injectors, that is where a bit of Redex comes in, works like drain cleaner on the little holes in injectors.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

madasafish

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Re: mot fail on emissions
« Reply #4 on: May 22, 2021, 06:06:52 AM »
My wife dives a small diesel prone to clogging up everything with soot
Before every MOT I drive approx 25 miles at 4,000 to 5,000 rpm  (in whichever gear is needed to achieve that).

Passes MOT emissions with ease.

DeadBoB

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Re: mot fail on emissions
« Reply #5 on: May 22, 2021, 10:46:16 AM »
I'm sure the forum can help, we need to know a few details.
The history of your car.
Why did your car not have the sensors in the exhaust?
Please advise  details of your car, model year, engine capacity.
Please let us have a few details about the sensors you installed, new or used,  part numbers,  price and source.
Have you installed the sensors in the correct positions, they are not interchangeable, they are quite different,  one measures flow , the other measures exhaust gas composition. did you remember to remove the protection  covers from the sensors before installing them?
The MoT test produces a paper printout giving the results of the emissions test,  do you have the printout, please post the figures on the printout, it may give the forum members  a few clues as to the problem and a solution.


Diagnose Dan for a Youtube video on sensors and how to tell if the sensors are working or faulty



i believe its the 1.2, bought last year no history (mrs had a C70 mot fail so needed a replacement), EML was on, wouldn't clear with my OBD reader, thought nothing of it until mot fail, additional markings in paint on the engine leads me to believe a possible engine swop has occurred.
First fast idle- CO-6.76, HC-814 Lambda 0.805
second fast idle, CO-6.87, HC-879, Lambda 0.792
« Last Edit: May 22, 2021, 10:52:17 AM by DeadBoB »

embee

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Re: mot fail on emissions
« Reply #6 on: May 22, 2021, 11:39:31 AM »
From those figures I'd guess it's running at full rich "clamp" (i.e. at the end of the range). It could be a temperature sensor is not connected/faulty (thinks it's fully cold) though I'd expect a check-engine MIL light on for that. Obvious thing to check is if the lambda sensor connectors/wiring are actually complete, if they were missing when you got the car it suggests a background story of some sort of damage/interference. Are you sure the sensors are the correct type?

E27006

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Re: mot fail on emissions
« Reply #7 on: May 22, 2021, 11:59:35 AM »
From those figures I'd guess it's running at full rich "clamp" (i.e. at the end of the range). It could be a temperature sensor is not connected/faulty (thinks it's fully cold) though I'd expect a check-engine MIL light on for that. Obvious thing to check is if the lambda sensor connectors/wiring are actually complete, if they were missing when you got the car it suggests a background story of some sort of damage/interference. Are you sure the sensors are the correct type?
When Lambda > 1  = excess air to fuel, = weak, when   Lambda <  1 excess fuel to air  = rich.
A good value  for MoT Lambda is 1.00 +/-  a small margin

The Lambda on the car is way below 1.00 ,  , with the engine hot can you detect  a smell of petrol in the exhaust gas from the tailpipe?

Testing the temperature sensor ( basic test)

On the instrument cluster ,  the temperature  indicator symbol for the  coolant,  a symbol , not a gauge,  does the coolant symbol  show when the engine is cold and does it extinguish as the coolant temperature rises after a few minutes of the engine running?

Note to Jocko:  is it worth suggesting the free Torque  phone app and a £10  OBD2 ELM 327 type bluetooth adapter from Ebay to help diagnose  this problem?
« Last Edit: May 22, 2021, 12:14:27 PM by E27006 »

embee

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Re: mot fail on emissions
« Reply #8 on: May 22, 2021, 02:39:31 PM »
I suppose the question is whether the ECU is intending to run it that rich or whether it is trying to overcome a faulty reading from the lambda sensors. Running at L=0.8 the sensor outputs should be fully high and the ECU should be driving it towards lean, but that appears to not be happening (it's unlikely to have anything richer than L=0.8 available within the working range so is at "clamp", i.e. hard at the end of the adjustment range). If the sensor outputs are at zero it will consider the mixture to be lean so will drive it rich. If the outputs don't change it will go rich as far as it can in trying to get the sensors to go high so it can then start feedback and cycling (L=1.0+/-).
If the temps are correct, look at the sensor outputs. If high then something else, if they are zero then find out why. If they are high, check whether the signals are getting through the connectors and actually arriving at the ECU. If the sensors say high but the ECU doesn't see it, then it will continue to drive it further rich to try to "correct" the mixture even though in reality it is already far too rich.

Jocko

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Re: mot fail on emissions
« Reply #9 on: May 22, 2021, 07:42:31 PM »
Note to Jocko:  is it worth suggesting the free Torque  phone app and a £10  OBD2 ELM 327 type bluetooth adapter from Ebay to help diagnose  this problem?
I use a stand-alone OBD II reader. I tried an ELM 32 with my laptop but it wouldn't connect. I used something like this: https://www.amazon.co.uk/Diagnostic-Professional-Scanner-Battery-Storage/dp/B091B4ZQNV/ref=sr_1_1_sspa?dchild=1&keywords=obd2+reader&qid=1621707867&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyNDUzVjlLRTBIVFFHJmVuY3J5cHRlZElkPUEwNjUyOTUxMjRVVVJGT0lZSktESiZlbmNyeXB0ZWRBZElkPUEwNzk4MDYwMlVOS0gyRDY4NExQMiZ3aWRnZXROYW1lPXNwX2F0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=



Now I use my ScanGauge E, which is permanently connected to the OBD port, though I never have any errors. Well, until now!


springswood

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Re: mot fail on emissions
« Reply #10 on: May 23, 2021, 08:42:59 AM »
Quote
EML was on, wouldn't clear with my OBD reader,

Do you know the error code?
"Indecision is a terrible thing"
Or is it? What do you think?

E27006

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Re: mot fail on emissions
« Reply #11 on: May 30, 2021, 08:34:24 AM »
Is the problem solved?
Please post the solution.

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