High CO: cat or engine problem?

[eurasiaoverland]

Hi guys

The truck is due its annual technical test which includes an emissions test.

Last year, the test showed high CO when the engine was at speed. HC levels were very low, and lambda was spot on. The truck had at the time just had an engine rebuild so I'm confident that the engine was, and still is mechanically perfect; it has plenty of power, gets great fuel economy, doesn't use a drop of oil and runs very nicely.

At the time I had an issue with the idle staying too high, and to fix this problem (after the technical test) I ended up replacing the O2, EFI coolant temperature and air inlet temperature sensors. The two temperature sensors solved the high idle problem for good.

So my question is, could my high CO reading have been fixed by changing one of these sensors (like the idle)? Or is my cat worn out?

Having low HC and high CO seems a bit odd to me; one would expect both of these to be either high or low, as they are both converted by the same oxidation catalyst withing the cat.

Has anyone had a similar experience?

Note that for cars of my vintage, there is no NOx test. A new cat would be very expensive

Thanks

EO

 

[19963.4lsr5]

I'd just take it in. The high CO could have been from the rings not being bedded in yet with the fresh rebuild. Your getting good fuel milage......


Sent from my iPhone using Tapatalk

 

[HiluxSurf SSR-G]

what does lambda represent?

 

[eurasiaoverland]

what does lambda represent?

It's basically a calculated value of oxygen in the exhaust gases to check whether an engine is operating sufficiently close to the stoichiometric misture ratio (i.e. the correct proportions of fuel and air being burned).

 

[HiluxSurf SSR-G]

i see. does it also apply to diesel engines? what would be the ideal value of lambda?

 

[eurasiaoverland]

i see. does it also apply to diesel engines? what would be the ideal value of lambda?

Traditionally no, since only fuel is metered in a diesel engine. But with very modern diesels this is starting to become part of emissions control, but that' nothing I know about. I've given up on diesels since they became so sensitive to bad fuel and therefore not suitable for my needs.