high lambda value and secondary air system

oldvolvos · Post by **oldvolvos** » 14 Feb 2021, 07:27

When recently testing our Volvo V70 1997 B5254S, it was diagnosed with too high a lambda value in the exhausts; 1.07, accepted level 1.04.

Now, the story is long and complicated; in a first test, the lambda value was even higher, but exchanging the exhaust system rear part (big crack) brought it down to the present value. Before testing, I also had a start problem, when the engine would start and then rapidly stall. That turned out to be the MAF. I bought a used one and the car ran.

I now have two error codes; P0422 and P0410. The first one is main catalyst, and is probably just an effect of the real problem, so I'll disregard that.
The second one indicates the secondary air injection system.
I have checked the system, and found that the pump was not working: it was full of water. Actually, there was so much water I was surprised that it could have been working at all for quite some time. However, when I was looking for the engine fault earlier, the system did not return the P0410 code, so it looks like it was OK in December. Lately, its been rather cold around here (below -10C), and it is possible that the water froze and the pump burned out.

So, it looks very much like my lambda problem lies with the air pump. However, I can not understand how a lack of secondary air can lead to too high a lambda value, which indicates too much air in the exhaust.
So, I am also a bit suspicious of the used MAF I bought. It might not have been exactly the type needed.

Does anyone know if a lack of secondary air can actually increase air concentration in the exhaust? I was thinking maybe the pressure would be too low in the exhaust and the engine would therefore take in too much air for the combustion, but that does not feel like a good explanation.

The secondary air pump for Volvo (Pierburg) is a bit expensive (>300 euro). Would it be possible to replace it with a cheaper model, like Topran?

cheers

Post by **RickHaleParker** » 15 Feb 2021, 06:52

oldvolvos wrote: 14 Feb 2021, 07:27 The secondary air pump for Volvo (Pierburg) is a bit expensive (>300 euro). Would it be possible to replace it with a cheaper model, like Topran

Volkswagon used the same pump with slightly different hardware. You can take the hardware off a Volvo pump and transfer it to a VW pump. Then install it on your Volvo.

Volvo Air Pump Fix Tutorial (MVS)