What will kill a cat on a E38 740iL? - BMW Forum - BimmerWerkz.com
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#1 (permalink) Old 08-14-2009, 08:09 AM
42, The meaning of life
 
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What will kill a cat on a E38 740iL?

Had the transmission fluid changed today and the mechanic decided to start poking around to see what he could find. He tells me that I need two new catalytic converters, right hand trailing arm and that driver side air bag sensor is faulty so I need a new $800 air bag module and on it goes.

The car has only done 137,000 km and I have never had to replace a catalytic converter before (on any other vehicle I have owned), he claims that they are choked up and causing too much back pressure which is why the car is having trouble revving easily. Can anyone provide any input into why this may have happened, and what I can do to confirm a pair of dead cats before I go and buy new ones? If they are dead, is there a recommended performance cat on the market, or are they all pretty much the same?

Any suggestions on the Airbag sensor issue, as far as testing it further to isolate the individual fault. The Air Bag warning light comes on as it should in the test position of starting, then goes off once the car is started, then comes back on about 5 seconds later.

Is there anything special about doing a wheel alignment on the 7 (E38) series, or can anyone of the tyre places do the job properly?
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#2 (permalink) Old 08-14-2009, 08:45 AM
OMFG another one!?
 
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AFAIK, bad mixture (sometimes caused by bad O2 sensors) can result in over rich exhaust with too much incomplete combustion which then over works the cats. There should be no unusual process doing a wheel alignment.

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#3 (permalink) Old 08-15-2009, 05:46 AM
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Wheel alignment on an E38 must be done via lazer, dont go to a back street garage!!.

Cats, firstly I would get a smog test done to ascertain if the cats have gone as it seems very strange that both have gone ???? after the smog test go out on the high and give it a good 50mile blast at say 100mph, then redo your smog test and see what the difference is.

Airbag, check under the drivers seat that all the connections are tight, this sometimes happens if the drivers seat has been removed at some point, you could try disconnecting the battery for 20 minutes to reset the ECU, Neg off 1st and on last.

If you dont have the OBC screen, make sure you have the radio code it may or may not need a code.

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#4 (permalink) Old 08-15-2009, 08:13 AM
42, The meaning of life
 
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Originally Posted by marti5 View Post
Wheel alignment on an E38 must be done via lazer, dont go to a back street garage!!.

Cats, firstly I would get a smog test done to ascertain if the cats have gone as it seems very strange that both have gone ???? after the smog test go out on the high and give it a good 50mile blast at say 100mph, then redo your smog test and see what the difference is.

Airbag, check under the drivers seat that all the connections are tight, this sometimes happens if the drivers seat has been removed at some point, you could try disconnecting the battery for 20 minutes to reset the ECU, Neg off 1st and on last.

If you dont have the OBC screen, make sure you have the radio code it may or may not need a code.
The machanic is pointing his finger at the cats for being "clogged" and excessively restricting the flow of the exhaust and thereby limiting the free revving of the engine. In park the engine will wind up quite nicely, but under load it struggles somewhat. The car has just competed a 750 - 800km trip at highway speeds (120km/h) and returned what I consider to be fairly good fuel consumption figures of 8.8l/100km. Will the exhaust composition be different between a healthy cat and a defective one? Is there an easy way to test if the Oxygen sensor has joined the cats in the scrap yard?

Are there replacable bushes on the trailing arm, or is it one disposable item? Does the wheel alingment process involve the rear axel as well as the normal front end adjustment? In Australia I have heard this referred to thrust alignment, or is that something different?

I'll have a poke around under the drivers seat tomorrow and see if I can find any suspect connections. with the disconnection of the battery, do I need to have any codes etc for the car to operate? The vehicle has an OBC with GPS & TV rather than just the basic radio. How long do I leave the car to "reboot" once the battery is reconnected? Do the keys need to be in the ignition when the battery is reconnected?

Thanks for your help WS & M5
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#5 (permalink) Old 08-15-2009, 09:07 AM
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Quote:
Originally Posted by brettski View Post
The machanic is pointing his finger at the cats for being "clogged" and excessively restricting the flow of the exhaust and thereby limiting the free revving of the engine. In park the engine will wind up quite nicely, but under load it struggles somewhat. The car has just competed a 750 - 800km trip at highway speeds (120km/h) and returned what I consider to be fairly good fuel consumption figures of 8.8l/100km. Will the exhaust composition be different between a healthy cat and a defective one? Is there an easy way to test if the Oxygen sensor has joined the cats in the scrap yard?

Are there replacable bushes on the trailing arm, or is it one disposable item? Does the wheel alingment process involve the rear axel as well as the normal front end adjustment? In Australia I have heard this referred to thrust alignment, or is that something different?

I'll have a poke around under the drivers seat tomorrow and see if I can find any suspect connections. with the disconnection of the battery, do I need to have any codes etc for the car to operate? The vehicle has an OBC with GPS & TV rather than just the basic radio. How long do I leave the car to "reboot" once the battery is reconnected? Do the keys need to be in the ignition when the battery is reconnected?

Thanks for your help WS & M5
If the o2 sensors had gone they would have the thrown up a fault code, I find it strange they haven't, if both the cats's have gone the engine hasn't been running properly for a long time, A cat is a very hardy piece of equipment. Your fuel consumption looks fine, I would still get a smog test this will show if the cats have gone, If its found they have gone then this does NOT mean the o2 sensors are dead as well.

Trailing arms are normally a complete unit as are most of the suspension parts on the E38, unless you have specialist equipment.

The wheel alignment should include all four wheels, although you can just have the fronts done, but I always have the lot done.

You do not need any codes for the car as you have the screen, if you are worried, take the + (red) cable off the battery for 20 minutes and then reconnect.

But the best way is to take both leads off.

The car will re-boot straight away.

Most people don't realise the E38 actually takes 16 minutes to shut completely down after you remove the key and lock the doors....Fact.

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#6 (permalink) Old 08-16-2009, 05:43 AM
42, The meaning of life
 
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Originally Posted by marti5 View Post
You do not need any codes for the car as you have the screen, if you are worried, take the + (red) cable off the battery for 20 minutes and then reconnect.

But the best way is to take both leads off.

The car will re-boot straight away.

Most people don't realise the E38 actually takes 16 minutes to shut completely down after you remove the key and lock the doors....Fact.
I disconnected both battery leads for the 20 minutes as you suggested, while it was sitting there discharging I checked the connectors under the drivers seat and it dawned on me that you may have been referring to the left hand side seat which in Australia is the passengers seat. Are the sensors your referring to always under the drivers seat regardless of which side its on? Anyway when I reconnected the battery the Air Bag warning light came back on as it has previously.

What is the OBC doing for the 16 minutes after the vehicle is locked?

With regards to not creating power, it seems to be worse when the motor is cold, if you don't nurse the throttle when the motor is cold, it just drops back to what would be an idle until you lighten up on the throttle. Once it warms up its more responsive, but still not what you would call good, especially down low. When the motor is first started the idle is very rough for about 20 - 30 seconds.
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#7 (permalink) Old 08-16-2009, 07:20 AM
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Your drivers seat is correct as the drivers seat connections control the passenger side, if you disconnect the drivers seat the passenger seat will not operate.

The Obc shuts down all the modules in the car one by one and this takes approx 16 mins dependant on the level of options you have fitted.

I will do some more thinking on your throttle problem.

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#8 (permalink) Old 08-18-2009, 12:55 AM
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just throwing in my 2 bit's worth,have you checked with a 2nd shop?,my 7 runs smooth hot or cold,I did learn the hard way to code the radio after disconnecting the battery,and the car had to relearn my driveing style!! if the cat is bad you should notice a rotten egg smell out back ...at least that 's what mine did,I dumped the cat with a strait pipe. a damm lot cheeper..
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#9 (permalink) Old 08-18-2009, 05:44 AM
42, The meaning of life
 
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Upon further reflection about the clogged Cats diagnosis, something doesn't quite stack up, unless I am on the wrong line of throught about what a Cat does and how it does it.
If the Cats are blocked or at least severely restricted, this would, as Kenjh points out, stop them from performing their compound changing function, which would result in a rotten eggs smell in the exhaust which I haven't noticed. The impact on performance would also get worse with higher revs with the increase in the volume of exhaust being passed through them. To me it sound like there may be a throttle position, vacum or Airflow sensor that is faulty. But then again I am not all that trained in things mechanical.
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#10 (permalink) Old 08-18-2009, 08:41 AM
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As ive said go get a smog test, this will rule out cats and o2 sensors......all you have mentioned above can easily be found out with diagnostics.

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#11 (permalink) Old 08-18-2009, 01:01 PM
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I was thinking u usually use the front bumper or the tire.... then I realized not the animal

The car doesn't burn oil does it? Cause sometimes the OSV dies and burning oil could foul the cats...

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#12 (permalink) Old 08-19-2009, 06:34 AM
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I was thinking u usually use the front bumper or the tire.... then I realized not the animal

The car doesn't burn oil does it? Cause sometimes the OSV dies and burning oil could foul the cats...
I haven't noticed any smoking either at start up or when driving. I haven't had the car long enough to figure out if it is using oil as yet. There aren't any warning lights or service messages relating to the engines operation displayed.

I had to look up what OSV was(Oil Seperation Valve), and found this article that describes the problem associated with this item and the process to repair it, but it specifically mentions the 1998 version of the M62 engine, was the problem rectified in later releases of the motor, specifically the M62TU which is what I have?
Notes/Photos for replacing the BMW E38 (M62) Valve Cover gaskets.
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#13 (permalink) Old 08-20-2009, 03:56 PM
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The PSV (aka osv on earlier models) is a diaphragm which fails around 80 to 120K dependant on how and where (temp/country) the car has been driven,when it fails big time the vehicle will still start, but omit a bid cloud of smoke which will dissipate.

The new part when ordered from BMW as this is basically the only supplier of the above mentioned, is now a one part unit + seal, unlike 5years ago several parts.

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#14 (permalink) Old 08-21-2009, 08:29 AM
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Is the Vanos in the frame instead of the Cats??

I was reading in one of the other BW threads about the performance issues that worn Vanos O'Rings can cause, and the symptoms seem to be all to familiar.

What are the symptoms of a failing vanos?
Overall loss of torque and power, particularly in the lower RPM range, < 3k. Bogging then surging at 3k RPM. Uneven power distribution and RPM transition. Engine hesitations in the lower RPM range, < 3k. Louder idle and intermittent idle RPM hiccups. Difficult takeoffs. Loss of power and bogging when AC on. Increased fuel consumption.
Double vanos cars with the M52TU engine (98/99-00) experience cold weather cold start idle jolts and possible stall.


Beisan Systems - Procedures - Double Vanos Procedure

This extract specifically related to the M52TU engine. Is there a similar implementation of the Vanos system on the M62TU engine that is prone to the same problems? If so what is the procedure to confirm the Vanos as the cause, and then resolve the problem?
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#15 (permalink) Old 08-23-2009, 05:25 AM
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Well I think I have identified at least part of the bottom end performance issue. I disconnected the Air Mass Sensor and hey presto we have a significant improvement in performance. I am going to try cleaning the AMS mesh out and see if that makes a difference, otherwise I guess I'll be buying a new AMS. Still way cheaper than a pair of Cats, and easier to fit.

Are there any issues with leaving the AMS disconnected until I can clean it out, or does the ECU simply accept that its not present and work with the remaining sensors? Interestingly there haven't been any service messages about the AMS being disconnected.

Does anyone know of a performance AMS unit suitable for use on the M62TU motors? Do the performance units make a significant difference?
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