Failed mot on emmisions again

david451

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Hi guys, I have a 200slk, got oil in the wiring and made the mod at the front of the engine. I never got into the control box but damaged the lamber at the back of the engine, I changed it but its failed this year again. I never changed the wiring so I guess it's my own fault, but there cant be any oil left in the bastid surely.

It wont rev up above 4000 rpm standing still, and all the readings are off the scale on the gas test, same as last time.

I cut back the wiring on the old sensor and there seems to be no oil in it, and the new one fitted last year only had a a little oil in the plug. Do you think the oil has shorted it out at the plug rather than seeping right into the sensor down the wiring, which I thought it had done on the old one. I cleaned the plug out with brake cleaner but its still the same.

I checked the flap on the maf and it seems to be ok.

Any advice appreciated.
 

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Hi David, if the engine lamp is not on, then it should not be anything to do with the wiring, the car will not rev over 4k in N, so that is normal.

We normally do a high speed run in 3rd to clean the engine out, prier to the test.

Oil is an odd thing as id does not short out electronics, indeed many things run in oil for cooling but it does upset cars somewhere.

Has the car been plugged into a code reader.

Welcome to the forum
 
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david451

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Hi David, if the engine lamp is not on, then it should not be anything to do with the wiring, the car will not rev over 4k in N, so that is normal.

We normally do a high speed run in 3rd to clean the engine out, prier to the test.

Oil is an odd thing as id does not short out electronics, indeed many things run in oil for cooling but it does upset cars somewhere.

Has the car been plugged into a code reader.

Welcome to the forum

The engine management light is on, been on since a year ago when I changed the sensor behind the engine and it passed. Cut open the old probe and it was full of oil, but cant smell any from the wiring on the new one fitted but it's failed on everything. However it would be fair to say that the plug had oil in it.

My car is a manual and I'm sure it does rev right up stationary. The vehicle has been off road for about a year with the occasional start, anything else that would give that fault.

Kind of new here, had my merc since new and keeping it until I die, retired now and only do about 3000 miles if I'm lucky a year and it only goes out in good weather during the summer months. It a 2000 model on an x plate black.

Oh and I am a mechanic, but kind of fooked by not being able to read the codes.
 

brandwooddixon

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STAR read would be first step as this will tell you what has tripped the engine warning light. Depending on where you are there may not be an independent and so you'll have to pay the MB price.

One of our members with a similar setup to yours found his MAF failed due to blocked breather pipes forcing oil into the inlet pipe. This may have happened to you - hence reluctance to rev freely.

Another point when replacing parts, ensure that you buy OEM froma reputable supplier as a lot of the pattern parts (lambda, MAF) are a false economy as they go out of spec pretty quickly.
 

Alex M Grieve

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One of our members with a similar setup to yours found his MAF failed due to blocked breather pipes forcing oil into the inlet pipe. This may have happened to you - hence reluctance to rev freely.

A good point - I can remember having blocked breather pipes on older cars many years ago. Are these a regular service item though? If not, there are probably plenty around which could do with cleaning?
 
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david451

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A good point - I can remember having blocked breather pipes on older cars many years ago. Are these a regular service item though? If not, there are probably plenty around which could do with cleaning?

I remember the last time it wouldnt rev up either but once moving it goes onto the limiter. Think if I am going to keep this I need to get a reader of some sort, however the guy who failed it says his cost 5000 quid and it's in aberdeen at the minute getting updated, hence why I have not had it read.

Sitting in the house debating on wheither to just buy another probe or wait and have it read incurring another 50 quid, which busts my ass.

It was quite interesting to see inside one cut open, it's like a horse shoe bit of metal inside which must heat up, and another which clips into it with the wires on it. It must read the temperature of the gasses, and if I could have put it back together again, cleaning the burnt oil off the contacts it might have worked, but it's crimped and you cant after attacking it with a hacksaw.
 

shayes

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Could this low mileage per year be the cause - short journeys - something the Lamda sensors do not like?


Just a thought
 
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david451

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Could this low mileage per year be the cause - short journeys - something the Lamda sensors do not like?


Just a thought

Last time the oil did it for certain, but this time I'm not sure and its been laid up for a year, so you could be right.

If I keep going like this I'm gona have a bandalerro of em.
 

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No MB will go past 4k in park, and that has been so for years, so no fault there. A good indie will tell you what the problems are for £25-£30, where do you live in the UK.

Most code readers will check the engine management and cost up to £60 and will do many cars


With the engine lamp on the O2 sensor has shifted from its settings to try and compensate for something
 
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david451

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No MB will go past 4k in park, and that has been so for years, so no fault there. A good indie will tell you what the problems are for £25-£30, where do you live in the UK.

Most code readers will check the engine management and cost up to £60 and will do many cars


With the engine lamp on the O2 sensor has shifted from its settings to try and compensate for something

I think its a job for the code reader as you say.
 

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Checking the Lambda sensor is reasonably straight forward.
Your car will have either a 3 or 4 wire sensor.2 of these wires will be for the heater element-one should have battery voltage,the other should provide a good earth(use a multimeter with the engine running to check this.Pierce the wires,don't disconnect the plug).When cold the resistance,engine off,plug disconnected,across the heater element should be in the region of 5ohms.
The other one or two wire/s are the sensor circuit-with the engine at full operating temperature,pierce the sensor wire & check the voltage.You should get a fluctuating reading in the range of 0.2 to 0.8 volts.It should be a rhythmic fluctuation (eg;0.3 to 0.6 over a period of about a second).If it's a 4 wire sensor,then the remaining wire is earth,pierce it & check for a good earth with the engine running.If it's a 3 wire sensor,check that the exhuast offers a good earth to the negative post on the battery.

If you get a good result on the above,you can (almost certainly) rule out the sensor.
If you get a low voltage reading on the sensor wire(0.2 volts or less) then the sensor must be faulty,as you have high emmisions-if it's high then get the system read off,as the fault probably lies elsewhere.
 

meanie

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One other thing regards the lamda;with a soft (brass) wire brush,carefully clean any muck or crap off-don't ask why,I don't know,but it does work sometimes (really only if there is a lot of muck covering it).

Also,aren't these engines prone to cracked manifolds-this could affect the ability of the sensor to do it's job properly.
 
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david451

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One other thing regards the lamda;with a soft (brass) wire brush,carefully clean any muck or crap off-don't ask why,I don't know,but it does work sometimes (really only if there is a lot of muck covering it).

Also,aren't these engines prone to cracked manifolds-this could affect the ability of the sensor to do it's job properly.

Its the 4 wire probe, had one of them to bits to see whats inside, not much. The second one died because it was full of oil and nobody at merc told me there was a problem with oil in the wiring when the first one went.

The one in just now "3rd" has only been in for a short while but traces of oil were found in the plug when I took it off, however stripping back a portion of wiring never reveiled oil in the wiring which makes me think having it laid up for a year has caused something to stick.

I will have a go at testing it.

I hope the manafold aint cracked.

On long term thinking plan, do you think I should hang onto it or move on. Are they worth the effort, had it 9 years and kind of like it but ??
 

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Its the 4 wire probe, had one of them to bits to see whats inside, not much. The second one died because it was full of oil and nobody at merc told me there was a problem with oil in the wiring when the first one went.

The one in just now "3rd" has only been in for a short while but traces of oil were found in the plug when I took it off, however stripping back a portion of wiring never reveiled oil in the wiring which makes me think having it laid up for a year has caused something to stick.

I will have a go at testing it.

I hope the manafold aint cracked.

On long term thinking plan, do you think I should hang onto it or move on. Are they worth the effort, had it 9 years and kind of like it but ??

Give in now === never :D:D
 

meanie

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One other thing regards the lamda;with a soft (brass) wire brush,carefully clean any muck or crap off-don't ask why,I don't know,but it does work sometimes (really only if there is a lot of muck covering it).

Also,aren't these engines prone to cracked manifolds-this could affect the ability of the sensor to do it's job properly.

Can explain the cleaning bit a bit now-the sensor element creates its' own voltage,dependant upon the difference in oxygen levels in the downpipe & outside,so this is where the cleaning helps when they're 'crappy'.

As far as getting rid,a harsh point of veiw as I'm in the trade.If I were you,I'd probably keep (you don't rely on it for transport,relatively speaking it's worth sod all compared to what it cost you new) & I think that if it cost £300/£400 a year in maintenance then that's £6/8 a week.
 

brandwooddixon

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No MB will go past 4k in park, and that has been so for years, so no fault there.

Sorry Malcolm I don't think that this applies:
david451 said:
My car is a manual

David if you can get someone to read the codes then the £50 is money well spent. After all you replaced a lambda before and the engine management light remained on.

In the meantime, do you have the print out of the emissions test as I gather that can give some pointers to the type of fault.
 
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david451

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Sorry Malcolm I don't think that this applies:


David if you can get someone to read the codes then the £50 is money well spent. After all you replaced a lambda before and the engine management light remained on.

In the meantime, do you have the print out of the emissions test as I gather that can give some pointers to the type of fault.

co <0.30%vol
6-56%vol

hc <200ppm vol
1261ppm

0.970-0-030
0.827

The guy has his tester back and I have it booked in tomorrow morning, hoping its only a probe again, but if it is I'm going to have to alter the wiring connections at the probe to stop the oil left in the loom getting in again. The control box section of wiring seems to be fine, very slight, opened it up to check just in case and its dry.

I dont think the light goes out on its own on this model, after the last probe was fitted it passed no probs but the light remained on and I just left it, 50 quid they wanted to put the light off at merc.

Perhaps the partco probe is rubbish but at 75quid it sounded reasonable, where do you guys get your parts?
 

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Its often not the oil that gets into the probe but the oil that goes into the engine, this coats the sensor, and it tries to adjust the fuel ratio for a better burn.

Yes the lamp can only be put out on STAR though I have known some engines to self correct when we had that last fuel contamination problem.

Why not get one from MB and see how that goes, if the spec is the same as the original that may be the only problem
 
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