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Discussion Starter #1 (Edited)
Car ('95 M5) just failed the MOT on exhaust emissions. I don't have the figures in front of me but the CO2 was about 6% instead of .5 and the hydrocarbons were double with the lamda miles out too. Stuck it on a BMW test machine and it came up with an open circuit Lamda, and also the air flow meter was showing it had had 4 faults, but none current. Changed the Lamda and re-tested it and it made no difference, figures still terrible. Changed the Air flow meter which has ALSO made no difference....

The car drives fine and the fuel consumption has not changed....what the hell's wrong? Would the cats have failed and could it be causing the figures this high? What test can I do to narrow this down as according to the BMW box of tricks the car should now be fine.... I'm running out of things to check here, anyone got any ideas please?
 

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London Mike said:
Car ('95 M5) just failed the MOT on exhaust emissions. I don't have the figures in front of me but the CO2 was about 6% instead of .5 and the hydrocarbons were double with the lamda miles out too. Stuck it on a BMW test machine and it came up with an open circuit Lamda, and also the air flow meter was showing it had had 4 faults, but none current. Changed the Lamda and re-tested it and it made no difference, figures still terrible. Changed the Air flow meter which has ALSO made no difference....

The car drives fine and the fuel consumption has not changed....what the hell's wrong? Would the cats have failed and could it be causing the figures this high? What test can I do to narrow this down as according to the BMW box of tricks the car should now be fine.... I'm running out of things to check here, anyone got any ideas please?
Before you go to the cats, I think this may be agood case for a rolling road diagnostic. It sounds like your cars emsisons are running open loop as would be seen in wot (wide open throttle ). I would look at wiring to the Oxygen sensor & the wiring to the water temp sensor on the hot side of the thermostat, not the sender to the water temp gauge sender. If this is brittle or broken then the car will fuel for cold start.
That is common when you look at how much upheat the flylead & connector see here.

After that lot has been checked then maybe you can consider the worst case....

Regards
Farrell
 

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Discussion Starter #3
The actual figures it's running are...

CO 6.020 (max. limit 0.300)
HC 535 (max. limit 200)
LAMBDA 0.819 (max limit 1.030)

And having reset the consumption this evening and paid attention to it, spirited driving with air con on is returning about 17, I remember it closer to 20 as average. Good news if it is a sensor down as the cats will be ok :D

I did consider bad wiring etc etc but surely this would have shown up on the BWM diagnostic?
 

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Discussion Starter #4
Water temp sensor on the hot side makes no difference to the CO figures whether it's plugged in or unplugged. I thought disconnecting it would stall the engine. Sensor may be down or the wiring to it?
 

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London Mike said:
Water temp sensor on the hot side makes no difference to the CO figures whether it's plugged in or unplugged. I thought disconnecting it would stall the engine. Sensor may be down or the wiring to it?
If the engines already hot & the wiring or temp sensor is shot then itwont affect it as oil & water is already up to temp
Check for breaks in wiring. look at any vaccum hoses.
Failing that. Take it to PMW in Chelmsford (01245 496739)
They play & twiddle & read the faults till they bottom it out.

Dealers are sh*t at sorting problems like this.

Farrell
 

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Discussion Starter #6
UPDATE

I got the sensors the wrong way round. The rear sensor on the aly water pipe next to number 1 exhaust manifold has a blue top and 2 terminals. If I unplug this then the revs drop right off and it won't rev so it appears to be working. The front sensor on the thermostat housing is the one that makes no difference. Presumably this is just used for the cold start circuit and wouldn't affect the engine when it's up to temp. So the rear one appears to be working....

Yes, problem from hell. The local BMW garage is more than happy to book it in and solve it but as they admitted, it could take days....

Days = £££££££££££ :mad:
 

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London Mike said:
UPDATE

I got the sensors the wrong way round. The rear sensor on the aly water pipe next to number 1 exhaust manifold has a blue top and 2 terminals. If I unplug this then the revs drop right off and it won't rev so it appears to be working. The front sensor on the thermostat housing is the one that makes no difference. Presumably this is just used for the cold start circuit and wouldn't affect the engine when it's up to temp. So the rear one appears to be working....

Yes, problem from hell. The local BMW garage is more than happy to book it in and solve it but as they admitted, it could take days....

Days = £££££££££££ :mad:
Hmm...
That sounds as though its all working then.
Have you checked the intake & exhaust for leaks...
A cracked manifold is not unheard of on a 3.8. They are a quite intricate.

It sounds like some time twiddling with a diagnostic & a ramp are going t5o be reqd. I will bounce some ideas about with a collegue.
Its so difficult to to diagnose this type of fault with out having the car to hand.

Would hate to say its cats yet though.

I may come back to you with something more positive but ramp time does look likely but to do economically is the thing.
Some specialists will charge only if the fault is diagnosed while im not sure dealers have the same outlook.

Good luck
Farrell
 

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Discussion Starter #8
Spoke to the boss at PMW (good guy) and he suggested maybe fuel pressure regulator gone bad causing it to over-fuel. His first suggestion was air flow meter, but as he said, if it's been badly over-fueling for a while then the cats will be saturated and may take some time for them to clear. Bugger, doesn't look like this is going to be an easy one to cure... :sad1:
 

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Discussion Starter #10
Possibly. I put some injector cleaner in the tank yesterday which may help. At 190,000 miles, things are inevitably going to start to fail I suppose....

The annoying thing is it drives perfectly... :rolleyes:
 

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Hi Mike

Hope your keeping well?

Don't know if this helps (my tech knowledge not that hot) but I had my throttle bodies balanced (CO2 check etc.) at William Jacks Sunningdale, because I was told the engine was running to rich. the technician logged 7 hours on the balancing side, primarily because, as he got cylinder six down to 0.5 from 1.3 and then went back to cylinder one, it had gone back up to 1.3. He repeated this process a number of times until he got as close to the stock value (0.5) as he good, he ended up on 0.8. In amongst all this (this is where it gets a bit sketchy with me) he said he had to take the DME out? This apparently stopped the Lambda probe compensating for the lean running of the previous cylinders?

I'm wondering if this could be the cause of your problems?

Have to say the beast is running really peachy now, although no noticeable change in fuel consumption.

They also only charged me £376 inc VAT for all of the above and an oil inspection. I supplied the oil.

Hope that helps

Regards

Brian








London Mike said:
Possibly. I put some injector cleaner in the tank yesterday which may help. At 190,000 miles, things are inevitably going to start to fail I suppose....

The annoying thing is it drives perfectly... :rolleyes:
 

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Discussion Starter #12
Hey Brian, how are ya? :)

Funny enough I was thinking about throttle balancing driving home tonight, I was going to do it tomorrow (I have the gauges here) It's definately rich and the tail pipes are black, and it seems to have dropped aboout 3 to the gallon. I'm not sure the throttles would cause this, it still feels like a sensor down, but I'll try it tomorrow....

Shame about Garcia, eh?
 

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London Mike said:
maybe fuel pressure regulator gone bad causing it to over-fuel. His first suggestion was air flow meter, but as he said, if it's been badly over-fueling for a while then the cats will be saturated and may take some time for them to clear.
Ehhhh, I had this, and all it takes to clear the cats is about 50 miles flat out on a deserted motorway. Well, actualy, a 12 mile stretch run up and down 2 times with a radar-detector on......hihaPerfect CO :thumbsup: ..... Except it was a 30degree Celcius day and the VERY hot car inside the workshop was not appreciated.....:hihi: Put's them right for complainig about being 0.05 too high:byee55amg in the first place. And there are 2 brands of pressure regulators for the V8 which are NOT interchangeable...... Guess which one they ordered :mad:
 

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Discussion Starter #14
I probably did 50 miles tonight at high speed/low gear trying to clean the cats out. Checked the tailpipes when I got home and they are both soot-black. It's over-fuelling for some reason.... grrrrrrr
 

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mike, have you tried another testing station, maybe the gas analyser was dodgy!
FYI my tailpipe's are always sooty, yet my 'cons2' is 24.6mpg I regularly sit at 120 ish on the motorway or anywhere that's feasable, naturally traffic conditions don't allow for long bursts. Checking the plugs the other day - body is sooty, electrode grey?, I think that's ok.
Hope yours is nothing too serious.
Cheers,
Phil.
 

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Yeah, my tailpipes always sooty and when I check the plugs prior to the throttle balancing, they were sooty round the thread but the centre was a lovely buscuit brown?

I do believe there is a relationship between the lamda probe and the DME, each compensating the other for lean running, (lean running meaning engine failure territory; I previously had pistons burn out due to this) so that you always run a rich mixture?

As I said before William Jacks maybe able to do you a deal on the balancing/CO2 check. Their pricing book suggests its an hours labour? this wasn't the case in my situation (7 hours) as I believe it to be a much more complicated scenario than we are led to believe.



Phlem5 said:
mike, have you tried another testing station, maybe the gas analyser was dodgy!
FYI my tailpipe's are always sooty, yet my 'cons2' is 24.6mpg I regularly sit at 120 ish on the motorway or anywhere that's feasable, naturally traffic conditions don't allow for long bursts. Checking the plugs the other day - body is sooty, electrode grey?, I think that's ok.
Hope yours is nothing too serious.
Cheers,
Phil.
 

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London Mike said:
I probably did 50 miles tonight at high speed/low gear trying to clean the cats out. Checked the tailpipes when I got home and they are both soot-black. It's over-fuelling for some reason.... grrrrrrr
Mike
If the lambda circuit is still open loop which will initiate wot fuelling strategy, then I suggest disconnection the battery & leave for 15 mins or so & reconnect to see if the fault clears.

If still overfueliing then the only thing is checking the senors & wiring for any breaks until you find which sensor is putting the wot calibration in.

One other thought is the ignition coils. Is there any low speed misfiring...?

All the comments made by the Guys on plugs etc are valid. Mine are dark round the base with a straw coloured electrode. I guessed that you had already looked at the plugs but you cant discount things.

One thing to note.
If you have managed to get raw fuel on the cat monoliths, the fuel will destroy the washcoat & no amount of spirited driving will save them.

I wish I could get hold of your car myself. I feel like I could perhaps do more mate. Im sorry.

If worst comes to worst, I will speak to Pete & PMW & see if we can arrange to get together at his place to nail this sucker.

Good luck

Farrell
 

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Discussion Starter #18
Hi farrell

Thanks a lot for the input. No low speed misfires, infact if I don't look at the MPG I'd have no idea there was a problem, car's driving fine. Just changed plugs and didn't notice anything strange. Great idea for re-setting the system, it does seem like WOT calibration. I'll disconnect the battery (although it's a major PITA to re-programme the stereo :) ) and see if it cures it

By the way, I'd like to nominate you for 'Expression Of The Week' for 'cat monoliths' :D

Mike
 

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Wouldnt want to hijack this thread but just had my mot done last week - got these results:

Fast idle

CO: 0.17 % vol
HC: 65 ppm vol
Lambda: 1.007

Natural idle

CO: .07 % vol

I know this passed but otherwise the numbers mean nothing to me. Can anyone enlighten me? and how do they compare with others?

Cheers

Frank
 

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M5e3438 said:
Wouldnt want to hijack this thread but just had my mot done last week - got these results:

lFast idle

CO: 0.17 % vol
HC: 65 ppm vol
Lambda: 1.007

Natural idle

CO: .07 % vo

I know this passed but otherwise the numbers mean nothing to me. Can anyone enlighten me? and how do they compare with others?

Cheers

Frank
Frank

CO: 0.17 % vol = Carbon dioxide level present in the tailpipe as a proportion of the overall volume of emissive gasses sampled over timed period of test.

HC: 65 ppm vol = Hydrocarbons are present in exhaust gasses in a variety of forms not all of which are sampled by the gas analyser due to its location in the tailpipe. Highly carcinogenic. A figure of 65 parts per milllion indicates good operation of the catalyst withy minimal excess fuelling.

Lambda: 1.007 = This is a bit more complex but is basically a function of the air to fuel mixture ratio. Approximately 14.5 Kg of air are reqd for complete combustion of 1Kg of fuel. This excess air factor or lambda is used to define this actual air to fuel ratio.

The above has a decisive influence on the composition of exhuast gas.
The conventional spark ignition engine with a closed loop catalyst afterburner produces max engine torque with a Lambda ratio of 0.9 & this ratio is used for full engine load operation.
Optimum fuel economy is achieved using a Lambda ratio of 1.1.
This mixture strategy coincides with low load load applications.
Ideally when the engine is also at idle / fast idle, low CO & HC would also result . NOx (Nitrogen oxides)however are at a maximum at this ratio so you should back away from this ultimate ratio of 1.1 to avoid excess Nitrogen oxide & possible misfires occuring at idle will increase HC emissions.

So for idle/ fast idle mixture, the ideal range of Lambda ratio move between 0.9 & 1.05

Your cars Lambda of 1.007 indicates good closed loop fuelling & catalyst afterburing performance.

I have tried to keep this simple & hope the figures make some sense.

When im out with my other half & mutual friends, Im banned from talking about Engineering or related subjects....... Cant see what her problem is really !


Take care
Farrell
 
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