Misfire in x3 Cylinder

[Chii]

Hi All,

My Zed (2007 3.0si) has been fairly poorly for a while now, I am looking for a second or third opinion - is it time to give up. Mrs Chii certainly thinks so..
If anyone could read and share their thoughts, it would be greatly appreciated!

When Cylinder 1, 2, 3, misfired first of all I had a good number of errors when using a scanning tool.
And for reference they are constantly misfiring rather than every now and then.
Errors were relating to Oxygen Sensor issues, Tank Venting Vale, and Catalytic converter 1 conversion & catalytic converter 1 conversion 2.

I've had x6 new spark plugs replaced
x6 ignition coils
rocker cover gasket & valve tronic gasket replaced as there was oil build up in the cylinders
cylinder head cover breather replaced
oxygen sensor banks 1 and 2 replaced

Still the car misfires in cylinders 1 2 and 3

I still have the tank venting valve error, and likely expect the catalytic errors to come back but don't want to keep driving it while misfiring

The specialist has said next thing to do is replace the whole exhaust and get the tank venting valve done at the same time
It's another chunk of money to do that and I would just like to hear from someone else there is a chance this will sort the misfires
In my mind it feels like an unrelated issue, granted it still needs doing but if the engine is shot I don't really fancy it.

Thanks very much for reading, please let me know what you think

 

[j3nks79]

I’m assuming he thinks you have a blocked cat?

 

[raymond.harper]

I saw a video on YouTube, where else, the N52 engine had misfire on cylinders 1, 2 and 3. The cause was the common earthing cable to the cylinders

 

[Rockhopper]

So whats common to cylinders 1,2 and 3 and not shared with 4,5 and 6? The exhaust manifold and the cat within it.

 

[Mike6]

What mileage is car on. I would discount whole exhaust system as misfire is only on one bank.

 

[Mike6]

Also specialise should be able to tell whether it is a fueling problem or electrical related.

 

[raymond.harper]

So whats common to cylinders 1,2 and 3 and not shared with 4,5 and 6? The exhaust manifold and the cat within it.

I think they do not share the same lambda sensor. which could be a source of the problem.

 

[Mike6]

He says oxygen sensors have been changed

 

[Z4Mariner]

It's possible your bank 1 cat is falling apart, but it's not the most common thing, so not my first thought. I would look hard at: 1) bank 1 upstream O2 sensor; 2) ground wire for bank 1 (cylinders 1 2 3) - it could be bad internally or not well secured to the correct stud.

Test for #1: Try running with the upstream O2 sensors unplugged and monitor result. If the only codes are for the O2 sensors, and not for misfires, you have isolated your issue. A bad (even though new) O2 sensor will affect all three cylinders in that bank. If your new sensors are not BMW or Bosch, I would replace them - at least the upstream sensors, because they control the fuel delivery.

Test for #2: Inspect carefully to be sure the proper nut is securing the ground wire to the correct stud. If that looks good, inspect the length of the wire visually. As a check, jump the grounding wire to the engine head with a heavy copper wire and see whether that eliminates the misfire.

See this post on another forum: https://www.bimmerfest.com/threads/misfire-on-1-2-and-3.1199401/

Best of luck ! Let us know how this goes for you.

 

[Chii]

Ahh, thanks so much guys for the replies.
Really appreciate your time!

What mileage is car on. I would discount whole exhaust system as misfire is only on one bank.

Mileage is 155,000
Do you mean don't do the whole exhaust but the manifold only? Or you are pretty much ruling the entire exhaust for this issue

Exhaust has an internal rattle and has been there a while. In honesty for a long time I thought it was knocking and didn't mind. When my local garage did take a look at it, checked everything was secured - and concluded the rattle was inside the exhaust. Could that be a failed cat?
The exhaust also sounds quite a bit "deeper" than it used to. It's still the stock one from new

I think the specialist is hoping it is the manifold for cyls 1 2 3

The replacement Sensors are OEM so they should be good.

I will check out that earthing in Test #2, thank you Mariner

I guess on the whole though from the replies, it is actually possible the exhaust may be the cause, but very rare.

Thanks again

 

[AveZ4coop]

It could be a blocked cat, I had this on a different car (a Peugeot V6) and it was very hard/expensive to diagnose. You could unbolt the manifold from the head and see if this makes the issue go away (Cheap to try). My mechanic found the problem by accident when he moved the car off the ramp while he had the exhaust off. Previously we had replaced all spark plugs, coil packs, sensors and even tried a replacement ECU.

I hope you get this resolved.

 

[Z4Mariner]

With the added information on rattle and 155K miles, a blocked cat seems possible.

Has the same shop done all the work that you described ? If your shop seems expert, and suggested the exhaust / cats, perhaps they have some other data or evidence that they could share with you ? Perhaps they have done a proper diagnosis but didn't communicate to you how and why they made their repair recommendation. If a primary cat has fallen apart, the debris from it will eventually pass downstream to the secondary cat in the center of the exhaust, which might lead them to suggest an entire exhaust – but see posts on this forum about passing MOT’s with no secondary cats.

A borescope camera in the upstream O2 sensor ports cat confirm a core breaking up or mostly plugged, but it takes some time = labor cost. A clogged cat can be confirmed by flow-testing the two banks individually for excessive backpressure. This can be done in a basic way via the O2 sensor ports with a pressure gauge. Well-equipped shops can check backpressure in a dynamic mode (see here for a BMW 6-cyl example: https://www.youtube.com/watch?v=jQqZAM6KK6c ).

I wish you good luck in confirming and fixing the issue !

 

[Rockhopper]

Your car has two separate exhaust manifolds which both have CAT's built in. The exhaust system itself then has a further CAT. My bet is that the front manifold CAT has collapsed.