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Discussion Starter #1
Is that whining noise when I start up - a pump which warms up the Kat to operating temperature, and thus lowering emissions on cold start ups?

Does it actually work? has anybody had an MOT with it not working? And still passed the emissions part?

I hear this part fails on alot of cars as they age, not abnormal I know - but I was wondering if it is worth replacing if it did ever fail.

Rgds
J
 

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There`s a air pump attached to the exhaust manifold that is activated by an electric clutch. It fires up for about 10-30 seconds on cold starts to pump air thru the exhaust.

I heard two reasons why;

One; the air dilutes the exhaust which allows the emissions out the back to pass certain emissions tests when the engine is cold. The cats aren`t up to temperature yet and can`t process the exhaust to the legal requirement.

Two; the air being pumped into the cat helps it process the exhaust to meet the legal requirements. Presumably if this is the reason, then the extra oxygen or other air component must aid the catalytic reaction at low temps.





If memory serves, the pump cuts out if the engine gets over 3500rpm, but that`s not a clever thing to do if the engine`s stone cold anyway.

The pump is not used much, so as age takes it`s toll, (remember the youngest E34 M5 is 10 years old this year, the oldest around 17 years!) the unit becomes noisy. It normally makes the car sound a little like a diesel, others report a whining as if a belt was slipping.



The pump doesn`t actually heat the cats.



Generally speaking, just leave it until the time it finally dies. If and when this finally happens, then you have choices;

One, buy a new exhaust manifold, which are a small fortune on these cars. The pump is bolted into the exhaust manifold if I understand correctly, which is a pain, as the bolts will be pretty much heat and time welded solid. Often the manifold breaks or bolts shear when removal attempted.
(Also, remember that conversation recently here, in which it was discovered that removing the exhaust manifold often snaps one or more bolts into the block... Ouch! $$$)

Two, remove the pump, hopefully without drama, and have a good welder weld a plate over where the pump used to be.

Three, the easiest option, ignore the failed pump and remove the relay/fuse (I forget which) which a member of this board said was in the fusebox under the rear seat. This stops the electric clutch engaging, so the failed internals of the pump are irrelevent.




The E34 M5 can be difficult to get thru an MOT when cold. Importing the car to the USA also had issues, as the 3.8s were tricky to get past the emissions test over there, I think it`s called the EPA.
This is rumoured to be why the 3.8 wasn`t sold over there.

The car will pass hot. The normal trick is to either have a friendly MOT place who know the score with the age and technology of the engine, and pass it anyway (ask your local independant who they use!), or pick a MOT station that is accurate and on time, then have a really good blast in the car before the test, so they get it with a red-hot engine and exhaust, so by the time it`s done the other checks, the cat is still glowing when the emissions are done. Works a treat.

If I recall, someone here getting a 3.8 car thru the EPA did this, blasted around the docks for a while before taking it back to the testers, it passed!





Hope this helps and is correct. If it`s not, I`m sure I`ll be shouted down and will edit the post accordingly! :)



Ivan.
 

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Discussion Starter #3
Hi IvanDias

Many thanks for the quick post and the info on it.

ok so it dilutes the emissions and also helps the catlytic process on start up.

I have really good set of headers just lying around - i will put them somewhere safe - as i mentioned on another thread about all the problems people were having about their headers - that I woul definitley keep mine now.

You are right - I bought the headers with 5 of the bolts removed where the small pipes are attached (two bolts per pipe) one set of bolts would not come off, but I will leave them for now. But I was wondering about what all these extra connectors/small pipes were doing on the headers. Now I know.

Oh well - lets hope I never have to replace my headers for a start, I think I will probably disconnect the pump's fuse once it gives in, and then get a new pump from BMW. By the way did the 3,6 have one? And if so does your's still work?

many rgds

J
 

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Jahangeer said:
Is that whining noise when I start up - a pump which warms up the Kat to operating temperature, and thus lowering emissions on cold start ups?

Does it actually work? has anybody had an MOT with it not working? And still passed the emissions part?

I hear this part fails on alot of cars as they age, not abnormal I know - but I was wondering if it is worth replacing if it did ever fail.

Rgds
J
Blip the throttle once , either before or after the sound starts , and you will get no sound at all.

:cheers:

ralph (vadas1)
 

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Kurt Ramsden said:
Ghost - can you confirm which relay to remove, and it's location?

Thanks
Sorry, my mechanic removed it for me during an inspection, I can ask him next time I take the car in.
 

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Discussion Starter #11
I think it should be more of a low humming sound - quite loud, as people turn and look as they think there is something wrong with your car.
 

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Yes when I first got my car I thourght there was something wrong but when I met with some of the others and they tolf me that the noise mine makes was quite quiet I calmed down. Then I read in one of the BMW books that this was added to reduce emissions from startup until the cats get warm.

Mine makes ,as you say J, a low humming sound not that loud but noticable.

Simon
 

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There are many, many posts about this pump here!

I've had mine replaced, so I know how it sounded when I got the car, when it was working, when it started not to work, then stopped working and I also know how a new unit should sound.

Firstly, the 3.6 and 3.8 cars have different control from what I gather, mine being a late 3.8 works like this:

When cold, after 30 seconds the pump will run and will run for 90 seconds unless the revs are increased above 3k or so or if the revs drop really low, ie the car labours. If I blip the throttle before the pump comes on or indeed when it is running it makes no difference, unless the revs increase above 3k or so as mentioned above.

The sound is like a deep air horn or similar and changes with revs/load. when my old pumps started to go, it started to get quiter and quiter, then eventually I looked and saw that it was not being driven when the magnetic clutch was engaged.
The new pump was quite for the first couple of cold starts but after about a week, it returned to it's normal loud horn like sound.

I think from memory, it cost about £600+ for the new one, well worth it for the wierd sound in these nice cold mornings.
 

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Discussion Starter #14
I think from memory, it cost about £600+ for the new one, well worth it for the wierd sound in these nice cold mornings.[/QUOTE]
-------------------------------

Plisken

You are as odd as I am ;) - I also like the sound, I suppose we all have to be a little bit strange to keep these cars - where else would we spend our money?
 

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Jahangeer said:
I think from memory, it cost about £600+ for the new one, well worth it for the wierd sound in these nice cold mornings.
-------------------------------

Plisken

You are as odd as I am ;) - I also like the sound, I suppose we all have to be a little bit strange to keep these cars - where else would we spend our money?[/QUOTE]

Do not worry I like the sound too and it maybe that my familiarity with the sound makes me assume that it is quiet. But I know that is loud enough for people in other cars to look at my car and wonder what on earth is under the bonnet. :D

Simon
 

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I had an ex girlfriend whos father owned an F40,

well, the cat pumps sound exactly the same as the M5 on start up !

So one morning he comes running outside naked cause ive started the M5 and he thinks his F40 is being stolen !

Oh we did laugh afterwards !
 

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I tend not to drive away in mine until the pump cuts out! :sad1: .....the funny looks people tend to cast my way if I drive off with the pump still running........a loud 'BRRRRR' noise over the normal engine growl ........

first time i heard it i thought it sounded like a cracked manifold! ouich

Still.....nice to know it works :wroom:

Scorch
:cool:
 

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I park in an underground cement lot. The reverb that thing gives down there is awsome! I have to wait until it shuts off to drive otherwise I set off at least 5 alarms on the way out. Good excuse to let her warm up a bit first anyways.

N
 

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nixter said:
I park in an underground cement lot. The reverb that thing gives down there is awsome! I have to wait until it shuts off to drive otherwise I set off at least 5 alarms on the way out. Good excuse to let her warm up a bit first anyways.

N
I used to do that! now Im rebuilding the motor,not saying that lettin it warm up on tick over caused the failure but May have had something to do with it! The handbook says start the car and drive it,no warm up period is necessary.I am sure someone else will second my thoughts?
 
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