Where have my 330Ci's 02 sensors gone? Help please.

[E63eeeeee...]

Hi everyone. Today I'm mostly baffled.

I have an early (June 2000) 330Ci. Last weekend it started idling roughly and revving itself, then stalling. I had a Google about potential causes, and a look at the OBD2 live data showed that only the precat bank 1 sensor was reading more than trivial voltage when the engine was running, the other three were showing tiny voltage or nothing, although they started to look more normal when I turned off. So that seemed a logical place to start. Had a look on YouTube, seemed a manageable DIY, ordered two precat sensors, opened the bonnet today, no o2 sensors. The cut-outs to access them are there but I can't even really see the headers. Feeling around, there are definitely headers there, but I can't feel anything like a sensor as far down as I can reach. I had a quick look at my other (2003 facelift) 330Ci and I can see the sensors easily, so I'm now thoroughly confused.

Other info, it's the earlier engine with the bolt-on coils rather than the push-on ones (I thought that was the M52 but my vin decoder says M54). It's had very little use and similarly little maintenance in the last 5 years before I got it so I'm fairly relaxed about throwing parts at it because I'm assuming as it passes 20 years old most things will benefit from swapping out anyway.

So any suggestions or advice appreciated before I turn up at a garage looking stupid. Is this normal because it's an early car and I need to access the sensors from elsewhere? Has someone swapped the headers at some stage for some with oddly situated sensors? Is the whole o2 sensor thing a red herring and I should try a different fix - the sensors could potentially have been reading like this for years?



You can see the cutouts in the heatshield and this much space in such a crowded engine bay does look a little suspect now I think about it.

[G600]

Assuming it's the same as an M54 engined Z4 that bracket is for the US market carbon canister or air pump, something like that so it being empty is normal, put you VIN in on realoem.com and it'll give you a parts manual showing the O2 sensors you should have.

Assuming it's a January 2000 car this shows 2 post car sensors https://www.realoem.com/bmw/en/showparts?id=BN52-E...

Strange

Edited by G600 on Saturday 5th September 11:06

[E63eeeeee...]

G600 said:

Assuming it's the same as an M54 engined Z4 that bracket is for the US market carbon canister or air pump, something like that so it being empty is normal, put you VIN in on realoem.com and it'll give you a parts manual showing the O2 sensors you should have.

Assuming it's a January 2000 car this shows 2 post car sensors https://www.realoem.com/bmw/en/showparts?id=BN52-E...

Strange

Edited by G600 on Saturday 5th September 11:06

Thanks G600. The bracket in the foreground is off the secondary air pump, I'd moved it out of the way so I could see what I was doing. It's the pre-cat sensors I'm after immediately. I've ordered an endoscope on the assumption that they're in there somewhere and if I can find them it might be possible to get at them without taking the engine or suspension out. I got the new sensors based on the realoem parts numbers, just can't find the old ones...

[helix402]

You can bin the aux air pump and fit a genuine BMW blanking plate to the inlet manifold. Doesn’t put an DME dash light on with the M52tu. Probably doesn’t on the M54. Try it and see!

[E63eeeeee...]

helix402 said:

You can bin the aux air pump and fit a genuine BMW blanking plate to the inlet manifold. Doesn’t put an DME dash light on with the M52tu. Probably doesn’t on the M54. Try it and see!

Thanks. My other facelift 330 with the M54 has had the secondary air delete and is fine but I'm trying to keep the older one completely stock, so since it's not causing any obvious problems will probably just stick it back on when I get the o2 sensors sorted.

[helix402]

E63eeeeee... said:

helix402 said:

You can bin the aux air pump and fit a genuine BMW blanking plate to the inlet manifold. Doesn’t put an DME dash light on with the M52tu. Probably doesn’t on the M54. Try it and see!

Thanks. My other facelift 330 with the M54 has had the secondary air delete and is fine but I'm trying to keep the older one completely stock, so since it's not causing any obvious problems will probably just stick it back on when I get the o2 sensors sorted.

Fair enough. I bin them as they often go wrong and take up space in the engine bay.

[clarkson22]

You may have the early catless manifolds if yours is a 2000 which were fitted to the m52tu engine aswell, the lambda sensors will be further down the manifold if you search m52tu exhaust manifold you will see where they bolt in

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clarkson22 said:

You may have the early catless manifolds if yours is a 2000 which were fitted to the m52tu engine aswell, the lambda sensors will be further down the manifold if you search m52tu exhaust manifold you will see where they bolt in

Brilliant, thanks. That looks a lot like what I can feel. Getting at them is going to be lots of fun. Do you know if access to the sensors is any better from underneath?

[clarkson22]

Yes mate just jack it up remove undertray and possibly the metal undertray and it's easy enough to get to , sometimes I've found letting the engine get to temp then trying to undo them is easier but dont burn yourself,

[E63eeeeee...]

clarkson22 said:

Yes mate just jack it up remove undertray and possibly the metal undertray and it's easy enough to get to , sometimes I've found letting the engine get to temp then trying to undo them is easier but dont burn yourself,

That's really helpful, thanks. Although having seen your M3 thread I think my idea of easy may be a little different from yours. Will give it a try, thanks again.

[Touring442]

Push fit coils arrived in mid 2003 with the E60.

Removing/replacing the cat manifolds on a 330i is one job I will never, ever do again. You couldn't pay me enough. I ended up taking the engine out when a third nut rounded off.