REPLACED CATS, NOW GROSS POLLUTING??? ONLY 90k MILES

[CertifiedGrits]

Hello everyone, first time poster! I'm really in a pickle here. I bought this Beautiful 1997 BMW 740i with knowledge that the cats needed to be replaced. I could hear them when driving, and you could definitely feel it if u took a hammer to the cat ever so slightly. Anyways, I took it to get smogged before doing anything,

1st smog attempt:

Failed for NOx at 15 mph (493 ppm)

- After test I did the following:

> Cleaned bank 2 oxygen sensors
> Changed Oil (much needed)

... back to shop


2nd smog attempt:

Failed HC at 25 mph (38 ppm), expected given I can hear the cats...
Failed NOx at 15 mph (854 ppm)
Failed NOx at 25 mph (989 ppm)

- After the 2nd test I did the following:

> Replaced both catalytic converters, (Magnaflow 448005 CA-EO COMPLIANT)

... back to shop again

3rd smog attempt:

Failed NOx at 15 mph (1609 ppm)
Failed NOx at 25 mph (1725 ppm)

At this point I'm failing for gross pollution regarding my NOx levels and I really don't know what to do! The car only has 90k miles and drives amazing. It's so impressive for a 97!! Anyways, I checked for vacuum leaks and couldnt find anything! My fuel trim levels and oxygen sensor voltages are fine as well!, All my other emissions went down and are pretty much sitting perfect according to lambda... but the NOx shot way up as soon as I got my cats replaced, does anyone know anything about this? I'm running out of options here. I'm very confused I don't know what else to do. I made sure the cats were hot before taking it in... I appreciate any feedback anybody can provide! I can provide pictures of smog papers too, thanks!

[jclausen]

At this point I would take the car to a good bmw independent shop have them take a look

[007008]

I've never heard of "cleaning" oxygen sensors. I would replace both pre cat sensors. They get slow as they get older.
Also The Magnaflow number you posted is not what magnaflow recommends. It's either 448004 or 418005.
https://www.magnaflow.com/collections/catalytic-converters?california=true

[alexisonfire]

put some 02 spacers on there...problem solved.

[Raudi Driver]

Or buy my cats. I can ship those

[Old525i]

Register in another state, drive in CA.

[Timm]

Is the replacement catalytic converter a two-way or three-way converter? Those results are consistent of a two-way converter that does nothing with Nitrogen Oxides.....

[CertifiedGrits]

I've never heard of "cleaning" oxygen sensors. I would replace both pre cat sensors. They get slow as they get older.
Also The Magnaflow number you posted is not what magnaflow recommends. It's either 448004 or 418005.
https://www.magnaflow.com/collections/catalytic-converters?california=true


Ok so I did a little research. What do you mean by recommend? The CARB (California Air Resource Board) website provides a long list of MF aftermarket cats that are smog legal for my vehicle specifically, so it seems.

However, when I go to the Magnaflow website, it says there are only 2 cats that are compatible with my car?

According to the website, the catalytic converter currently installed is not compatible with my vehicle in the state of CA.

Not sure how to feel about this, very confusing...

Is the catalytic converter wrong?

- - - Updated - - -

At this point I would take the car to a good bmw independent shop have them take a look

It is a two way, I'm trying to understand why the NOx almost double when I changed the cats... do I need a 3 way?

- - - Updated - - -


At this point I would take the car to a good bmw independent shop have them take a look

Do you think it could be much deeper than the cats?

[Timm]

You certainly DO require a three-way catalytic converter - the two-way converters are for diesels and were discontinued for petrol engines in 1981 due to the high Nitrogen Oxide output. So, there's your problem sorted, you need a three-way catalytic converter.....

[CertifiedGrits]

Okay so, I had my friend's dad look at it. He owns a shop that specializes in german cars, specifically BMWs... given the fact that this is not a SMOG repair shop, they could not provide a 5 gas analyzer... however they seem to think its the cats. The cats are 3 way converters I believe, but are just not efficient enough I guess... not really sure where to go from here, I'd like to try anything else I can before I go and buy new cats... any advice?

I should also mention they could not find anything wrong with it...

[alexisonfire]

You blew right passed my comment. 02 spacers and be done with it. those should work.

[noobbiker]

You blew right passed my comment. 02 spacers and be done with it. those should work.

How can spacers possibly get rid of NOX?

[racer2086]

Okay so, I had my friend's dad look at it. He owns a shop that specializes in german cars, specifically BMWs... given the fact that this is not a SMOG repair shop, they could not provide a 5 gas analyzer... however they seem to think its the cats. The cats are 3 way converters I believe, but are just not efficient enough I guess... not really sure where to go from here, I'd like to try anything else I can before I go and buy new cats... any advice?

I should also mention they could not find anything wrong with it...

It's highly likely to be the cats. Too much of a coincidence that you replaced them and it got worse, especially if everything else is in order.


You blew right passed my comment. 02 spacers and be done with it. those should work.

I don't understand how that would affect NOx?

[alexisonfire]

My mistake lmao
good luck!