[vin]

I have a 1.0L Corsa B with 161,000 miles on it. The EML came on last week with EGR failure reported. The car still starts and runs just fine but its MoT is due this week.

Two years ago I cleaned this EGR valve and fitted a blanking gasket, since then it has only just scraped through the MoT emissions test each time, usually on the retest. I was wondering if fitting a new fully functional genuine EGR instead of another lazy used EGR with a blanking gasket would improve its chances of passing the emissions test.

The engine is serviced every 5,000 miles and uses about 1L of oil for top-ups between services. No noticeable oil smoke from the exhaust and I still get around 48mpg. I am using 5w-30 synthetic oil.

My theory is that the EGR blanking plate is giving me good mpg but the NOx output is higher as a result and this is the cause of my hit or miss pass/fail on emissions.

 

[williamt73]

As far as I am aware NOx is not measured at MOT here in the UK - so blanking the EGR has no effect on emissions pass or fail.

You may need another theory.

 

[vin]

You are right. Only CO and HC are tested on the current MoT. I just looked at the MoT paperwork from previous years and my Corsa's CO was just over the limit and HC was low on the last refusal.

On the basis of determining what has changed in order to cause the effect, since blanking the EGR, MoT CO measurements have been borderline pass/fail.

Therefore my new theory is...

As EGR is supposed to lower both NOx and CO, fit a new genuine EGR and see what happens on the MoT.

Any suggestions for a backup plan if it turns out to be a rich running condition?

I have been back in the UK three years and I assumed that by now the UK MoT would be testing for NOx by now. NOx combining with HC is the cause of most lingering smog in cities around the world. Surely that's the point of using EGR?

 

[williamt73]

Any number of things may cause rich running. One or more of the engine management sensors which, while not completely failed, may be on the way out and thus giving a reading to the ecu to cause over fuelling. All of these sensors have finite lives. Given the miles your car has covered typical candidates could be the lambda sensor (O2), the coolant temperature sensor (CTS) or even the Mass Air fow (MAF) which also incorporates the air temperature sensor. Similarly any air leak in the induction system (or exhaust system if close to, or upstream of, the O2 sensor) may also cause the ecu to think the car is running weak and so it will compensate by injecting more fuel. Equally it could be the catalyst reaching the end of its life (so the car is not necessarily running rich, but the cat is just not cleaning the exhaust gas as it should) - especially if it has been changed in the past for a cheap after market system (these just don't last more than a couple of years).

These, however are just guesses. From this distance it is impossible to say accurately. How would you check either of these components? You could measure electrical resistances across each sensor to check if it is within spec. Possibly better would be to drive the car while having some diagnostic kit plugged in (Op-Com) and monitor in real time the signals coming from each sensor. I don't know what they should be - but I'm sure they have been posted or discussed somewhere already on this forum.

Good luck.

 

[vin]

Thanks. O2 sensor, Cat, exhaust system, CTS and MAF all replaced within the last year.
I have an OpCom but no info on what correct sensor ranges should be.