BMW Forums : BimmerForums banner
1 - 20 of 22 Posts

·
Registered
Joined
·
101 Posts
Discussion Starter · #1 ·
Just taken my car in for an MOT, failed on a few things most notably the emissions test. The results were as follows.

Fast Idle Test
  • CO: 1.06% (limit 0.30%) - FAIL
  • HC: 84 ppm (limit 200 ppm)
  • Lambda: 1.03 (limit 0.97-1.03)

Second Fast Idle Test
  • CO: 1.04% (limit 0.30%) - FAIL
  • HC: 67 ppm (limit 200 ppm)
  • Lambda: 1.01 (limit 0.97-1.03)

Natural Idle Test
  • CO: 1.16% (limit 0.50%) - FAIL

OVERALL: FAIL

Any ideas at to what the problem may be? I'm fearing I'll need to shell out for 2 new cats.
 

·
BFuk Legend
Joined
·
11,712 Posts
At first glance i would say it may be faultylambda sensors. The HC and Lambda is all within range.
You can test if the cats are working with an infared thermometer.
The gasses coming out of the cat will be HOTTER than the gasses going in.
First thing i would do i get the fault codes read and see what that throws up :thumbsup
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #3 ·
Having thought about it some more, I assume the cats are fine because the HC level is ok.

I shall get an OBD scan done or is there an easy way to test the Lambda sensors?
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #5 ·
Thanks steve, much appreciated. However what I still don't understand is how it's possible the Lambda sensors are faulty if the emission test shows the Lambda value is ok?!

Or to put it another way if the Lambda sensors are faulty should it fail on the Lambda test?
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #7 ·
Just got a BMW specific scan done and nothing flagged up what the problem might be.

Guys at the garage saying it could be crankcase breather, air leak somewhere, dodgy spark plug etc etc. Basically they want to examine it for 2 hours. This is getting expensive!
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #10 ·
Cheers I saw that and had a go with a £5 multimeter from Maplin, wasn't very successful, didn't get any readings off either sensor. A friend who works for GM reckons you need one of the decent Fluke meters to get any sort of reading.

I've managed to rig up an electronic circuit that uses a LM3914 IC and a LED bargraph to test it more acurately (it's a basic form of oscilloscope). I shall have a go tomorrow.

A couple more questions though if I may.

Why does my 730 only have 2 sensors where as other models have 4?

If the sensors are gone/on their way out, shouldn't the engine manangement light come on?
 

·
Registered
Joined
·
20,393 Posts
As the sensors get old they lose efficiency, the DME has NO idea the sensors are going bad.

Simple comparison, how do you know your eye sight is any good? unless you compare it with someone else or have it tested you could think everyone is the same as you :D

A lambda sensor is like this, there's nothing to tell it that what it's seeing isn't correct.

The same with a engine temp sensor for the DME, it can read the coolant as 130.c, but it's actually 85.c, you will only pick it up with diagnostic equipment :thumbsup
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #12 ·
My friend who works for GM has e-mailed asking me if the engine has an air pump for oxidising the CO and HC.

a) Do I have one?
b) If I do, could this be the problem?

The cats are fine by the way, I checked the temperatures before and after with an infrared thermometer.
 

·
Registered
Joined
·
20,393 Posts
My friend who works for GM has e-mailed asking me if the engine has an air pump for oxidising the CO and HC.

a) Do I have one?
b) If I do, could this be the problem?

The cats are fine by the way, I checked the temperatures before and after with an infrared thermometer.
Like this number 1 here http://www.realoem.com/bmw/showparts.do?model=GF22&mospid=47511&btnr=11_1427&hg=11&fg=50 or number 1 here http://www.realoem.com/bmw/showparts.do?model=GF22&mospid=47511&btnr=11_1508&hg=11&fg=50.

Have the vacuum pipes been checked ? http://www.realoem.com/bmw/partgrp.do?model=GF22&mospid=47511&hg=11&fg=45

And the live data checked, engine coolant temp sensor giving the correct readings?
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #14 ·
I took it for a diagnostic but I think they were trying to con me into giving them car for a while and then charging me a mountain of cash.

I've gambled on the lambda sensors, went to change them tonight and the old ones are stuck solid. Will have to get a garage to loosen up with a gas torch or something.
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #15 ·
It goes from bad to worse. Got the lambda sensors changed. The emissions have gone up!!

The hydrocarbons have skyrocketed to about 270ppm. The only test that went down was the idle CO level.

Bloke at the garage said it might be worth doing 200 mile of driving to clear the cats out of unburnt fuel. He says the cats sounds fine. Annoying whatever the hell the problem is.

I would say that the car idles better as a result of the new sensors.
 

·
Registered
Joined
·
20,393 Posts
O2 sensors do deteriorate with age, so you will find when the car is fixed it will really run smooth and should be better on fuel.

You really need to have the induction pipes, vacuum and engine breather pipes/system fully checked over, if all proves to be good then check the live readings on a BMW scanner to see if the appropriate sensors are giving the correct readings :)
 

·
Registered
Joined
·
101 Posts
Discussion Starter · #17 ·
Just been to have another emissions test done and the readings are as follows:

Fast Idle Test

*CO: 0.87% (limit 0.30%) - FAIL
* HC: 67 ppm (limit 200 ppm)
* Lambda: 1.01 (limit 0.97-1.03)


Second Fast Idle Test

* CO: 0.98% (limit 0.30%) - FAIL
* HC: 69 ppm (limit 200 ppm)
* Lambda: 1.01 (limit 0.97-1.03)


Natural Idle Test

* CO: 1.09% (limit 0.50%) - FAIL

The CO readings are lower than the first test. So far I've changed the lambda sensors, cleaned out an oily spark plug and coil near where the dowly seals leak. The air pump is ok, as is the throttle body hose. The idle seems good too.

The garage are recommending changing the cats which they can do for £440 inc vat. Seems quite a good price to me. They're not 100% certain it will work but fairly confident. Should I take the plunge?
 

·
Registered
Joined
·
20,393 Posts
If you do get new cats fitted make sure they are not really cheap ones, as they are not as efficient and will fail quickly, there are some new standards being introduced which all Cats will need to meet, otherwise they can not be sold.

Regarding your question, yes I think new cats will sort the emissions out, but bare in mind that if you do still have a problem there then a rich mixture will knacker the Cats prematurely.
 
1 - 20 of 22 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top