VR failed MOT on emissions

[Rado87 10]

So, the beast went for its MOT today after 3 years in the workshop and ****e load of money spent! Only to fail on emissions. Had the codes read and all that came back was inlet manifold temp sensor. Has anyone else ever had this?

[Dox 22]

You may find this useful

 

 

EMISSIONS HELP

 

CO high, co2 low hc high, o2 high - rich mixture with ignition misfire

 

CO high, co2 low hc high, o2 low -faulty thermostat or coolant sensor

 

CO low, co2 low hc low, o2 high - exhaust leak after cat

 

CO low, co2 high, hc low, o2 high - injector misfire, cat ok

 

CO high, co2 low, hc medium to low, o2 high - rich mixture

 

CO high, co2 high, hc high, o2 high - injector misfire, cat not working, combination of rich mixture and vacuum leak

 

CO low, co2 high, hc low, 02 low, good afr and cat operation- system normal .

lambda typical range 0.97 to 1.03 [ ideal lambda 1 ]

The emissions limits to be met are specified for both the fast and normal idle tests. At fast idle, CO must be at or less than 0.2%, HC at or less than 200 parts per million (ppm), and the lambda value(1) must be between 0.97 and 1.03. At normal idle, CO must be at or less than 0.3%.

[Rado87 10]

Cheers Dox. Looking like a coolant sensor then. Although, do you think the inlet manifold sensor could be the culprit seeing as that was the only fault code present? The stats brand new so hope it isn't that! If it is a coolant sensor, which one would you try first? In my head it would be the blue ECU one, giving the ECU false readings maybe?

[seanl82 23]

Blue supplies the info for the Ecu, so worth changing. Again iat sensor is quick and easy to change, so get it swapped out.

[Dox 22]

Heres my fail from earlier this year

 

I gave the car a full service including plugs, fuel filter (not changed in my ownership), fuel pump (it was noisy) and a cts to get a pass

 

 

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[Dox 22]

The temp sensor was £24 with the seal from vw

 

The old plugs

 

 

 

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[fendervg 30]

ECU coolant sensor rarely goes in my experience - that's the blue one. But cheap to replace if it hasn't been done - buy VW, Bosch or VD0.

 

The inlet manifold temp ones are a piece of **** and a bad design. I've heard of people moving them to the airbox for better readings.

 

The stat has nothing to do with fueling.

[seanl82 23]

I've heard of quite a few blue temp sensors being well out of spec, and recently too. Erratic idle, cutting out, and poor emissions being symptoms. You can monitor temps on VCDS which has shown them to be shot.

[fendervg 30]

There's a simple test with a multimeter and a bowl of boiling water. If the sensor is not working the ECU doesn't switch from cold to warm running map - hence the poor emissions. When cold, all bets are off on emissions figures.

[Dox 22]

There's a simple test with a multimeter and a bowl of boiling water. If the sensor is not working the ECU doesn't switch from cold to warm running map - hence the poor emissions. When cold, all bets are off on emissions figures.

 

Its not that simple, it has to read correctly from something like -50 degrees to +150 degrees, the range is not linear either so the only way to truly check it is with a known good sensor heating the water and comparing the 2 as the water temp increases.

 

There is a graph in the Bentley manual

[Dox 22]

 

 

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[fendervg 30]

It's only a linear reading because that is how that particular temp sender design works. The blue one only needs to read hot or cold. The problem is people buy cheap ones or use second hand ones - but always worth testing before doing the work. I tested a new one from VAG and it was duff, my original one was fine after 20 years or more, and with cheap ones you take your chances. IMHO only.

[Dox 22]

It's only a linear reading because that is how that particular temp sender design works. The blue one only needs to read hot or cold. The problem is people buy cheap ones or use second hand ones - but always worth testing before doing the work. I tested a new one from VAG and it was duff, my original one was fine after 20 years or more, and with cheap ones you take your chances. IMHO only.

 

You're wrong, it has to read all the temps the engine is capable of running at to supply the correct amount of fuel for that temp.

 

The Bentley graph above is not linear (a straight line) its curved.

[Tigerfish 10]

Also worth checking that the manifold temp wire and the black fan temp wire haven't been inadvertently swapped. That was the reason vagcom was throwing the inlet sensor fault on mine. The black sensor is either on or off, hence the open/short circuit fault.

Edited July 26, 2016 by Tigerfish

[fendervg 30]

I'm just putting it out for discussion and stand to be corrected. I have the Bentley as well and all the VAG service manuals for the VR.

 

The Blue sender is linear because the senders all use the same design. It doesn't need to be I believe. The other variations re temperature come from the intake sender which measure the temperature of the air in the throttle body ( which is cooled by the coolant).

 

Cooling and fuel injection are two separate but related systems that interact with each other closely. The ECU controls fuel delivery only, it has no control over the cooling system and only uses various temp related inputs from it and the O2 sensor (lambda) and the TPS etc.

 

The VR looks complicated at first, but Bosch Motronic is a relatively simple system with only a few inputs to the ECU from the various senders compared to more recent systems on modern cars.

 

You are way more likely to have a wiring fault, short in the loom etc than a dodgy sensor with a car this age.

[Rado87 10]

All excellent info guys, thanks. Tigerfish- I think that may have been the issue. Just to confirm, what colour cables go to the black coolant temp sensor in the stat housing? Mine were blue and green but now I've swapped them over there black and yellow. The blue and green go to the inlet manifold temp sensor.

[Tigerfish 10]

All excellent info guys, thanks. Tigerfish- I think that may have been the issue. Just to confirm, what colour cables go to the black coolant temp sensor in the stat housing? Mine were blue and green but now I've swapped them over there black and yellow. The blue and green go to the inlet manifold temp sensor.

 

Blue/green should go the IAT sensor, black/yellow to the coolant sensor.

[Rado87 10]

Spot on. You were right then, bugger me! Hopefully that's all that was causing high emissions then!!?

[Rado87 10]

So, I've swapped the connections around on the air intake sensor and the black coolant sensor and also fitted a new air intake sensor, BUT emissions still high, all 3! My question is, does anyone think/experienced, a high flow k and n cone filter causing high emissions? I'm thinking maybe the extra air intake results in over fuelling, thus raising emissions? I've put the standard air box back on and it does seem to idle more smoothly and after a blast round the bypass definitely smells different, less rich and more Catalytic convertery! 😜 I've had live data done and all the sensors seem to be operating correctly.

[Dox 22]

Why don't you post a pic of the emissions fail sheet?

 

I'll copy it and post it elsewhere where pro techs lurk, its what I did and someone posted this below.

 

 

EMISSIONS HELP

 

CO high, co2 low hc high, o2 high - rich mixture with ignition misfire

 

CO high, co2 low hc high, o2 low -faulty thermostat or coolant sensor

 

CO low, co2 low hc low, o2 high - exhaust leak after cat

 

CO low, co2 high, hc low, o2 high - injector misfire, cat ok

 

CO high, co2 low, hc medium to low, o2 high - rich mixture

 

CO high, co2 high, hc high, o2 high - injector misfire, cat not working, combination of rich mixture and vacuum leak

 

CO low, co2 high, hc low, 02 low, good afr and cat operation- system normal .

lambda typical range 0.97 to 1.03 [ ideal lambda 1 ]

The emissions limits to be met are specified for both the fast and normal idle tests. At fast idle, CO must be at or less than 0.2%, HC at or less than 200 parts per million (ppm), and the lambda value(1) must be between 0.97 and 1.03. At normal idle, CO must be at or less than 0.3%.

[Rado87 10]

Id love to Dox but I can't for the life of me work out how to do it! Its quite frustrating tbh! Anyway, results were as follows;

CO % volume 7.107

HC ppm 498

Lambda 0.812

[Dox 22]

I took a pic with my phone and used tapatalk to post the pic, its easy and that's from a techno-dunce

[Rado87 10]

Ha, same here! Ill have a go.....

[Rado87 10]

 

 

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[Rado87 10]

Yay! Spot on, cheers Dox. What day reckon to the results then? K and N to blame?