Hi, ive been working on fixing up my skoda fabia mk1 1.4 16v BKY. Took it for its MOT today and it only just passed emissions I was told and is running rich with too much fuel going into the engine. Anyone know what the fault for this could be? Thanks!

Any warning lights?

If so, get a code reader and/or VCDS on it.

 

Otherwise, begin looking at lambda sensors, MAFs etc etc. Currently tracing a similar issue on my 1.2 12v BME.

Pre-cat lambda probe is the most likely culprit, CTS is also a suspect.

Had replaced the catalytic converter with one that didn't include a pre cat catalytic converter, would this make any difference? Thanks

The pre-cat only helps by accelerating the warm-up phase.

 

Theoretically, with a properly warmed-up engine, there should be no difference but I don't know the nuances of the whole operation, whether there are differences in lambda probes part numbers, ECU values, etc. 

 

I give my car a good ol' Italian tune-up before going in (just to make sure its cats are up to temp) and it passes with flying colours. 

Pre-cat is what the ECU relies on for closed loop running, post-cat is for emissions only, pre-cat is generally a wide band probe on most 16V engines.

It is wideband on a 2005 BKY.

 

I'm not sure if it's possible for the following to be relevant, but when was the condition of the engine air filter last checked?

4 hours ago, Breezy_Pete said:

It is wideband on a 2005 BKY.

 

I'm not sure if it's possible for the following to be relevant, but when was the condition of the engine air filter last checked?

Just checked now, looks alright? 

17 hours ago, AnnoyingPentium said:

Any warning lights?

If so, get a code reader and/or VCDS on it.

 

Otherwise, begin looking at lambda sensors, MAFs etc etc. Currently tracing a similar issue on my 1.2 12v BME.

No warning lights on the dash. 

Check in between the pleats to make sure they're not full of dust, but first impression is that's not too old/blocked. 

Do you have the emissions printout from the test? 

18 hours ago, Bjohn2544 said:

only just passed emissions

There are a few ways it can be 'only just OK', it might be useful to know (all) the actual numbers.

19 hours ago, Bjohn2544 said:

Just checked now, looks alright? 

It might just be the photo but it doesn't look that clean to me, try holding it up to today's bright sky and see how much you can see through it, you could try a tap and blow clean or if you compare it with a new clean filter you may decide to fit the new clean filter instead.

 

48 minutes ago, nta16 said:

It might just be the photo but it doesn't look that clean to me, try holding it up to today's bright sky and see how much you can see through it, you could try a tap and blow clean or if you compare it with a new clean filter you may decide to fit the new clean filter instead.

 

For the price of a new filter, certainly worth trying.

Aye I'd just replace the filter. Nip to a local motor factors or something and get one bought. See where that takes you by way of fault finding.

I'm not sure that changing the air filter might resolve this issue but having a reasonably clean air filter and all the air and fuel systems  and their sensors clean will help.

 

If there's and air leak, or the computer thinks or is incorrectly told things are lean it may compensate with going rich, which the new cat won't like or MoT.

 

If the whole car is in reasonable running condition then the occasional Italian tune-up can help.  Doing it just before an MoT can perhaps help especially if the car doesn't then sit for ages before the MoT gets done.

   

Edited 15 July, 20223 yr by nta16
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