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Discussion Starter #1 (Edited)
Hi all,

A bit of background first ... I replaced my MAF sensors about 2 weeks ago, and was flowing over the magic 140 l/hour, with a 'top score' of 159 in 2nd gear.

However ever since I have felt power dropping ever so slightly. I re-ran the same test and achieved 122. Same stretch of road, temperature and gear, so I emailed board member DavidS who suspected my Pre-Cat O2 sensors were not sending the right information to the DME, and that they could probably do with replacing given that they have never been done.

So I rang BMW who did not have any in stock, however suggested NGK/NTK as they make a direct OEM replacement. The part number is OZA447-E27 and I purchased mine for AUD$125 (USD$94) each.

Installation requires the following tools

- 10mm socket + wrench
- Hammer
- adjustable Shifter (I did not have any open ended spanners handy).

1) Jack up car safely. The higher you jack it the easier it will be to get the required leverage on the sensor.
2) You will see that the sensor is attached to its socket under a plastic cover. make sure you know which sensor you wish to replace, I.E the one before the cat convertors (closest to engine)
3) Undo the two 10mm nuts with the wrench. Be careful not to strip them as they are a weak plastic.
3) Remove the connector from its housing and un-plug the O2 sensor.
4) With the spanner attach it to the o2 sensor. A few taps with the hammer and it should loosen.
5) unscrew and remove the sensor.

Installation is a reverse of the above. A few notes however

1) Be careful with the sensor.. it houses some metals that dont take too kindly to being dropped.
2) Before installation remove the plastic cover (pictured) on the NTK sensor. This is to protect the anti-seize paste.
2) the NGK/NTK ones come with the appropriate anti seize paste already on the thread so any more is not necessary.

Fuel flow is increasing and should return to normal after the ECU 'learns' the new (and correct) figures being fed to it by the new MAFS and O2 sensors.

I have attached some photos that may be of interest. Notice the difference between the old and new ones. It looks like one bank was running lean and the other rich. Most bizzare. I hope DavidS contributes to this thread.

Cheers,
Aaron
 

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Excellent post, Aaron!

It is easy to replace the O2 sensors. I just want to add this:

1. If you go with the Bosch sensors (which are not pre-lubed like the NTK brand) you absolutely must apply Never-Seize or something similair, or you have performed the very last O2 sensor replacement on that exhaust...

2. Apply the Never-Seize _only_ to the threads.

3. Torque to 50 (yes, fifty) Nm using a crow-foot and a torque-wrench.
(this is a very high torque to achieve with an ordinary length spanner)

4. You must not get grease or underbody stuff or anything on the visible part of the sensor or where the cables enter it. (The sensor works by the difference in oxygene concentration in the air and in the exhausts. It litterally must be allowed to breave freely, or it won´t work correctly.)

5. Sometimes you get O2 sensor errors beacuse of marginal MAFs, so better check the MAFs before replacing the O2 sensors.

Aaron, would you like to take a few fuel-flow measurements at regular short intervals so we can see how the adaptation changes after your installation of the new O2 sensors?

About the difference between the banks, I think you are right about one bank running lean and the other rich. Ergo, the S62 is an obvious Capitalist Machine.

Seroiusly, and this is just speculation, (oops, another Capitalist term) if one sensor gave the wrong O2 reading while the other was correct, the DME would adjust injector timing for each bank accordingly, and the O2 sensor that gave the wrong reading would get fouled.

David
 

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Discussion Starter #3
I will test over the next few days and report back results.
 

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aaronmiles said:
I will test over the next few days and report back results.
If they aren't working right just threaten them with that mean looking hammer of yours :eek:
Ken
 

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Discussion Starter #6
Hi David,

The power has returned, with l/hr over the past 3 days of

14.5c -> 151
17.0c -> 144
19.5c -> 148

The proof will be if the power drops off as the kms on the MAF's and O2's go up. I have not been able to replicate the 159, but it has not shown signs of dropping to the 120's that it was.

Cold start characteristics are also favourable at the moment.

Being monday here in Oz, the trawl to work has started again which puts on about 60kms a day so I will try and run a set every night and report the results.

Cheers,
Aaron
 

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Great, Aaron!

Just to clarify: are those numbers with new MAFs and new O2 sensors?
How many miles driven since the install of the new O2 sensors?

Cheers!

David
 

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Discussion Starter #8
Yes .. two new MAFS (032) and two new Pre-Cat O2 sensors (NTK).

142kms (88 miles) since installation.
 

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Just had my O2 sensor replaced. Luckily covered under the CPO extended warranty with $50 deduct. I finally got something out of that extended warranty:biggrin:
 

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Discussion Starter #10
I wish I had an extended warranty .. not because there is work that needs done, but more for a 'just in case', but here in Australia you get 2 years warranty and that is it, no extended warranties at all.
 

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aaronmiles said:
I wish I had an extended warranty .. not because there is work that needs done, but more for a 'just in case', but here in Australia you get 2 years warranty and that is it, no extended warranties at all.
A two year factory warranty! That's it??!! Is there a mileage cap that goes along with the 2 years!?
 

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Discussion Starter #12
100,000 kms I think...
 

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Torque-wrench and crowfoot

6spd said:
DavidS, there is a reduction in the Nm when you use the crows foot. Of course it depends on the length of the adaptor.
http://www.engineersedge.com/manufacturing_spec/torque_wrench_1.htm

Or you can cheat like me and turn it sideways(90degrees) and it shouldn't be that far off.
You are 100% right.

If the length of the crowbar (from center to center of each connector) is A and the length of the torque-wrench (from center of socket to center of force on the handle) is B then the actual torque delivered will be

(Set torque) x (A + B) / A

What I usually do is I use two torque-wrenches, and calibrate the torque-wrech + crowfoot combination, using one for measuring the actual torque and the other one for applying torque via the crowfoot.

I put a big hex bit inbetween to connect the crowfoot to the calibration torqe-wrench.

Anyway, what is important in this particular job is that 50 nm is rather much more than one would expect. I have no idea how critical this torque is.

David
 

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Re: Torque-wrench and crowfoot

DavidS said:
Anyway, what is important in this particular job is that 50 nm is rather much more than one would expect. I have no idea how critical this torque is.

David

Isnt it 55nm for the O2 sensor? That is what my fiche says and an extension only increases the torque applied. I guess if you go at 50nm with your extensions then you have a calculated 55nm, but I have no idea the dimensions of your torque wrench + adapter.
 

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Aaron, Great O2 replacement DYI. I started the project without seeing this post then had some big trouble getting the pre-cat's loose.

Wasn't all that comfortable with hammering away on it, until I came in and typed "replace O2 sensor" through the search function and found this great write up.

I then went back out and tapped the wrench with the hammer and it loosened nicely, again big thanks.

On a side note it appears that bosch is listening because they now have anti-seize applied on the threads.
 

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This board has been exceptional for any and all information regarding my M5. I really enjoy doing the work myself.

So far I have kept it fairly simple oil change, repalce pre-cat O2's, clean MAF's and replace plugs.

My next adventures will be post cat O2's, replace rear shocks and front struts, new K&N air filters, etc... and look foward to reading up on the related posts for help.

Thanks again to all for your help!!!!!!!!!!!!!!!!!!!!!!!!!!:cheers:
 

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Excellent thread, subscribing since I need to do this very soon. How easy is cleaning the MAF, and should I do that at the same time?
 
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