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Emissions faliure-170,000 miles what could it be 1.4 100BHP


benters
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help please the worldy wise folk of CL.

my X reg petrol sport has failed the MOT on emissions, the cat is a year old, the LAMBDA has been changed as I had hoped it would help (no difference) and there are no warning lights showing.

The car has never let me down and i don't want to scrap it, but what could the fix be ? The tester who has no interest in a repair job, reckons it could be valve seats, and just a tired engine. But some first hand experience will be useful, so advise away please !

the car cannot be worth much more than £500-750 even with a ticket. but being a sentimental old fool i would really like to repair and keep, if of course that is a practical alternative.

I guess an Ebay engine swap might be the easiest route and not a job that would be a problem for me to do, but is there something i am overlooking that could prove an easier alternative ?

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sure did. . .the engine really pulls very well, and doesn't smoke or give any symptons of internal issues at all . . . .i have the print out here from the MOT test and it reads.

At fast idle CO .67

At second fast Idle CO .61

At natural Idle CO .45

It seems to almost hunt or surge at idle but its very marginal. . .

that any help ??

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I assume you've changed the air filter and all that, fuel filter? Spark plugs etc? Do the 1.4 have a MAP Sensor? Also throttle position sensor.....

i wonder if you could lower the tickover for the MOT? ;)

Do you have an OBD2 tool?

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Interesting, you re ok at normal idle 0.45 and 0.5 is the limit, you're failing at fast idle, 0.6 vs limit of 0.3 so either not enough air or too much fuel

Throttle body might be a problem could need to clean it

MASS Airflow sensor (MAF) might need replacing

You have changed the Lambda sensor already, not sure if you have a 2nd lambda sensor like the GTi's do worth chnaging if you do

Catalyst might be tired or contaminated

Both MAF and Lamda can be checked with VAG.com or similar plenty of how to info on th web

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Go for a blast and get the engine up to temp, leave it cool down a bit then take the plugs out and see if they are the same colour noting which cylinder they came out of.

Check the colour against spark plug colour charts on the internet, but they should all be light tan colour if engine is running right.

Basic guide: http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

Just because the eml isnt on doesnt mean there arent faults being logged, so you need to get the codes read. Cheap £5 lead will let you do it yourself and save a lot of money.

Edited by Sausage
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thanks guys, appreciate the replies, I will do as suggested and report back. So far as I know the car only has one Lambda, but i will pop the bonnet at the weekend and have a rummage. Thanks again.

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This is why EVERY driver should buy an OBD2 tool. They're obnoxiously cheap, work with your mobile and can save you a fortune.

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Hi Skezza, being from the old school I didn't realise these things were so cheap !

I might represent others that still consider leads and sensors as witchcraft ! but I take your point and will surf and order today.

or it could just be me that is slow on the uptake of course :)

again all help is welcomed

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Guys, you are surpassing yourselves with top quality help and assistance ! the item is ordered, many thanks to you both

Edited by benters
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guys. I ran the check from the recommended OBD gadget and the only thing it kept saying was 'cant sync baud rate' this was after I chose the option of engine scan.

I did take a screen shot to show you but cant recall how to upload these :(

I am probably doing something wrong, but I did expect it to find a fault somewhere, unless of course the engine is so worn that its just a mileage issue and rebuild time !

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It sounds as though you used the fake vag com. You need to set the port in the options. Personally, the Bluetooth adapters are much easier to use imo but they tell you less.

You'll need to make sure all the drivers are installed etc.

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Hi Skezza, I did follow the pages of instructions which includes changing the port options as you suggest. it seemed to go as per the notes provided, but a pal has said he will come over to have a try with his reader, so I will let you know how that goes.

Thinking it is a mechanical issue, I will do a compression test at the weekend and see what that tells me. again I will report back so the knowledge is shared.

Peter

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Device manager / com ports / USB serial ch340.

make sure it's on COM 1 - 4.

if it's 5 or more then double click it and click advanced tab and change it to 1 - 4 in the drop down list.

You can up the baud rate of the port, try 38400, if any problems put it down lower.

In VCDS (lite) under program options tab, make sure com ports match device manager and click test. sometimes it doesnt work 1st time so do it again.

I have to unplug my lead and put it back in to make it work sometimes.

You can mess with the baud rate there too, but baud rate 0 auto negotiates best connection anyway.

Ignition must be on. :yes:

Edited by Sausage
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Hi Sausage, appreciate your reply. The instructions mention going to Comm port 4 which I did, they also refer to trying again as you suggest, which I did. but I will try again later and use your suggestion of 38400. I did perform the test as you suggest, and I think I am right in saying that you have to do this in order to save the settings, so that you can then run the scan.

its still all witchcraft to me !

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a long as com 4 refers to your lead (with it plugged in otherwise it wont show up in the com port list) it will say "usb serial ch340" assuming it's the same lead as mine.

Com port 1- 4 as VCDS only allows com ports 1 - 4.

Mine didnt work straight away either lol

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I must be a lucky boy. Mine worked first time, once I'd set the port obviously and still works first time. No unnecessary unplugging and what not. I think mine is COM port 4 as well

Been a bargain, just used it the other day!!

Ignition on, test something instead of engine, maybe convenience control?

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a pal of mine came over last night with the wireless version of a reader and the torque app on his phone and it wouldn't talk to the car :( we let the car idle and warm up which initially it finds a struggle, but after a minute or two it idles ok, albeit it is not at a consistent level, it slightly rises and lowers. So the next step was go through the mechanical stuff, so we cleaned the throttle body and re started the car with no difference, pulled the plugs, cleaned and gapped them no difference, did a compression test and it read 200 across all four cylinders. We then disconnected the temp sensor and bingo, it held its idle revs perfectly and sounded so much more even in its firing. We let it idle for twenty mins or so, with the thermostatic fan coming on as and when and it carried on idling like a sewing machine, so at last I think we might be getting somewhere. I guess if the temp sensor (green) is throwing out the wrong temp to the ECU then the car could be over fuelling and giving me the emissions issue ???

What do you experts reckon ?

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Strange that you can't read the codes, the ECU itself might be faulty worst case, 3 possibilities come to mind.

1/ temp sensor faulty telling the ECU it still cold and so running rich

2/ Temp sensor disconnect put the car onto limp mode in the ECU where it uses stored values and ignores the sensors

3/ doing the above masks the prolem and there is another issue in the control loop

Testing the temp snsor is simple if you have a multi meter, put it in a bath of cold water, gradually add hot water to simulate the engine warming up you should see the resistance change as the temperature rises

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Haven't found this elewhere, usefult to look at how the mixture control works.

begining with starting the engine, For starting a mixture with more fuel is required to do this the ECU looks up a value for the amount of fuel to be injected and ignition timimg internally this depends on air & engine temperature provided by the temperture sensors

Once the engine has started it runs at a fast idle controlled by the ECU and the throttle body to warm up the Catalyst, the temp sensor drives the ECU to reduce the idle speed as the engine warms up by controlling the throttle body.

Look up values for the ECU are provided by the MAF and temperature sensors.

This is all done using stored values in the ECU without feedback from the lambda sensors, this is called open loop control,

Once the catalyst is warm enough to work correctly the engine changes over to closed loop control where the two Lambda sensors provide look up information for the ECU. The reason for 2 Lambda sensors is to keep the mixture in the right range for the catalyst.

The pre - catalyst sensor provides the basic setting, the post catalyst sensor provides fine tuning to get the exhaust as clean as it needs to be.

Fly by wire or ECU control of the throttle body ensures that the mixture changes at a rate the catalyst can cope with during driving

Fault codes stored in the ECU allow for diagnosos of most of the possible failures that can happen.

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Cheers again for the continued advice guys. . . . . I now have a new temp sensor, clip and o ring to fit later today and see how I get on.

Fortunately for me the local MOT tester has taken pity on me and my car crisis recently and will do an emissions test for a pack of biscuits !, so hopefully this will be the answer and I can get the car back on the road. The lupo is more fun to drive daily than my other cars, so it will be good to get this sorted.

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