9A Hydrocarbons out of control.

[Albie 0]

My 2.0L 16V Just failed the MOT on hydrocarbons. After a head rebuild and rings/big ends replacement, I only have 100 miles on the engine. HC was just over the 200 pass mark on the first fast idle test at 218, then way over on the second chance idle test after 3 mins at 2500 revs at 501. CO was perfect at 0.129, (should be

 

In amongst other stuff I just went to check out and clean the throttle housing as it had also shown a fault code on his VAG-COM suggesting it couldn't see the throttle position switch. The switch meters fine but it may be a wiring fault. Could this affect the HC content and not the CO?

 

Also I had replaced the rubber housing which guides the air to the mouth of the throttle not long ago. I got a reclaimed part which seemed clean internally and was dry but looked a little rough on its surface so it may have had some dried off gunk in there that I missed. I have just found that sitting in the lower corrugations of the rubber is a small pool of dirty oil. I have no way of knowing if it has been there long or how it got there. The manifold interior is black of course but not oily in any way.

 

The rest of the intake tract surfaces are absolutely clean including the similar corrugations of the rubber cowling over the fuel metering unit. I had been wondering if I am drawing oil in and it is pooling there, but the cleanliness of everything else doesn't make that likely. I suppose the airflow could be scouring everywhere else and it is sitting in the grooves as it is out of the airflow. I suppose there is also a possibility that there was gunk in there and fuel and fumes from beyond the throttle have simply softened it and it pooled but it looked very like engine oil to me.

 

I know that the old Sciroccos I used to run had a problem with engine breathing where the Brillo pad oil separator on the top of the engine would gunk up and oil could slip past it into the airstream. Is there a likelihood of this on the Corrado?

 

Has anyone any thoughts on this? Of course no MOT means no opportunity to put miles on it and bed anything in any better! :(

[flusted 0]

Im not that clued up on HC but couldnt it be your cat?

[Albie 0]

Must admit it was in my mind at the time. I did ask the MOT guy that and he said that the cat was fine. How would I know without exchanging for a new one and testing again, (at "£whoknows" a time)?

[paul20v 0]

hi

hc is unburnt fuel its measured in parts per million ,

your car should have flew through at 218 or 500

what age is the car

there is earlier limits than what follows but there pre corrado

limits are as follows upto m reg cars and inclusive the limits are upto 1200 ppm and 3.5% (this is idle test only no fast idle required),

from N to august 2002 the limit is 200ppm and .3%

and there after the limit is 200 ppm and .2% which obviously does not effect the corrado

so there is no way your car should have been a fail ,unless its newer than m reg

 

 

at 218 your car is in very good health and no adjustments are needed

the high hc is generally an indication of timing out or knackered engine its not cat related , (no car needs a cat for test it only has to fall into the right emission limits)

hope this helps

if you need any more info i am happy to help

:salute:

[boost monkey 0]

Must admit it was in my mind at the time. I did ask the MOT guy that and he said that the cat was fine. How would I know without exchanging for a new one and testing again, (at "£whoknows" a time)?

 

partial retests are free within 10 days.

[paul20v 0]

Must admit it was in my mind at the time. I did ask the MOT guy that and he said that the cat was fine. How would I know without exchanging for a new one and testing again, (at "£whoknows" a time)?

 

partial retests are free within 10 days.

partial retests are free if the garage wants them to be but they are allowed to charge half the original fee

and the 10 day are working days excluding weekends and bank holidays , so effectively 2 weeks .