MAS Sensor?

[Dieselman]

Steve

Good to hear the old bus is back on the road.

I should have thought of catalyst as they really seem to be a common problem on modern Mercs, where the cat. is close coupled to the engine.

Keep this quiet but your tuning chip could well have created this problem as the extra soot blocks the cat.

I'm not surprised that the Mobilo Tech was not too good, as the Mobilo is now operated by Mondiel Assistance, not dealer techs. This came into force two weeks ago because of compaints that the dealer techs were recovering too many vehicles and not performing road side fix.

 

[Dave K]

DM (or anyone else) - where can one obtain a MAF at a sensible price? Still haven't measured the MAF output (huge leak in the central heating system at home over the weekend so I didn't get the opportunity) but I'm 80% convinced mine is FUBAR. Is it used on any of teh commercial vehicles I wonder (which seem to have spare parts at a much cheaper rate).

TIA

 

[Dieselman]

You could try a Bosch diesel centre but I doubt they will be any cheaper than the MB dealer.

The "commercial" ones are the same as 220 CDI units and are sold at the same price.

Unfortunately you are looking at £160 inc. as your best price. Standard price is about £170 + vat.
Just ask your dealer for discount, but be sure it's the MAF as they are non returnable.

To meter the MAF open the ECU connector and connect to Pin 21. This is the centre row second pin in from the left looking from front to rear of the car.

It's best to use a flylead into the car. Use the ground on the N/s inner wing for Gnd.

Feel free to ask if you need more info.

 

[mapleleaf]

Just a small point but is it a MAF sensor or a MAS sensor we have been posting about here , both sets of initials are being used and what do the initials actually mean???

or have I jkust missed something along the way.

The ML is running just fine now. good job the Tunit chip is invisible to the diagnostics system!

 

[jimmy]

Originally posted by Dave K
DM (or anyone else) - where can one obtain a MAF at a sensible price? Still haven't measured the MAF output (huge leak in the central heating system at home over the weekend so I didn't get the opportunity) but I'm 80% convinced mine is FUBAR. Is it used on any of teh commercial vehicles I wonder (which seem to have spare parts at a much cheaper rate).

TIA

I tried getting one for Graham when his packed up, I know a main Bosch dealer, we tried all the part numbers that were on the MAS unit, both Bosch and MB part numbers. None were recognised by the Bosch computer sytem 'bad part number' was all that we found.

I reckon Bosch and MB must have it all tied up so that you cannot get these from anywhere other than the dealers.

 

[Shude]

Isn't it the same actual sensor on every MAS application on MBs? I'm certain I read somewhere on this forum that the MAS for a Vito is available from your nearest MB commercial stealership parts dept for the paltry sum of £70. Then you have to swap the sensor with your dead one on the pipework specific to your car. Maybe it's time for a HOWTO?

 

[GrahamC230K]

Originally posted by Shude
Isn't it the same actual sensor on every MAS application on MBs? I'm certain I read somewhere on this forum that the MAS for a Vito is available from your nearest MB commercial stealership parts dept for the paltry sum of £70. Then you have to swap the sensor with your dead one on the pipework specific to your car. Maybe it's time for a HOWTO?

This should cover it really

 

[GregE240]

Originally posted by Shude
Isn't it the same actual sensor on every MAS application on MBs? I'm certain I read somewhere on this forum that the MAS for a Vito is available from your nearest MB commercial stealership parts dept for the paltry sum of £70. Then you have to swap the sensor with your dead one on the pipework specific to your car. Maybe it's time for a HOWTO?

You're right Nick - seem to remember Ricky (V12) posted about this a while back? I can't find the exact thread though

Speaking to Andy Gayle last week when I had mine done, certain models a replacement sensor is just that - the sensor unit itself. You unscrew the old sensor, bung the new one it, screw it in and away you go. Considerably cheaper than £200 for a replacement! However if you've got an A-Class beware! The MAS sensor is built into part of the airbox (I think) and its considerably more expensive than the sort of unit that fits our cars.

It seems to be an age thing - mine failed with 98K on the clock, yet both Grahams and Steve's failed with much less mileage.

Cheers,

Greg

 

[Dieselman]

The trouble is they're not all the same. Different sensors have different output characteristics.
You need to meter each sensor against airflow to determine this, or have Bosch and Pierburg reference data.

Incidentally the Pierburg unit fitted to the Vito and 220CDi outputs a digital signal not an analogue one, but has similar RMS voltages.
In thoeory this should work but may confuse the ECU and throw up an error, especially as it drops to 1v at idle instead of approx 2.1v.

 

[Dieselman]

Originally posted by steve_bcs
Just a small point but is it a MAF sensor or a MAS sensor we have been posting about here , both sets of initials are being used and what do the initials actually mean???

or have I jkust missed something along the way.

My understanding is MAF sensor, Mass Air Flow sensor. I'll check my invoice and wiring diagram.

Technically I believe it's the Air Mass Meter as it measures the Mass of air then calculates the flow.

Just checked the MB wiring diagram. "Hot film MAF sensor"

 

[Tan]

Originally posted by GregE240

It seems to be an age thing - mine failed with 98K on the clock, yet both Grahams and Steve's failed with much less mileage.

Mine failed at around 53K miles

 

[Dieselman]

here's a question.

Why do petrols go through more MAFs than diesels? (fact)

Is it because with the throttle opening and closing the MAF film overheats as it goes from full chat to no airflow very quickly? (supposition)

 

[sym]

Originally posted by Tan

Mine failed at around 53K miles

52,800 miles, and counting . . . . . . <SCARED !!!!>

s.


(now where did I put that K&N air filter . . . . .)

 

[Steve_Perry]

Originally posted by sym
52,800 miles, and counting . . . . . . <SCARED !!!!>

s.


(now where did I put that K&N air filter . . . . .)

You've got a few more miles yet My car was on approx 68,400 miles when the MAS was replaced and I think Graham's was on 61k miles when his was replaced.

Actually, I don't think MAS failures are related to mileage, they just go when they want to

S.

 

[sym]

Originally posted by Steve_Perry
, they just go when they want to

From an engineering point of view Steve , I'm sure you don't really believe that

. . . . surely there has to be some logical reason or physical conditions that speed their failure . . . . just what those conditions are remain a mystery.

I'm sure somebody more technically minded in this field will tell us all why one of these days . .

Anyway, the good news is that if it does go 'pop', I now know how to replace it at minimal cost, and without using a stealer !!!

(http://mbclub.co.uk/forums/showthread.php?s=&postid=27169)

never confirmed the part number / details on this one, but can find out very easily if anybody ever has the misfortune to need to know !!

 

[Steve_Perry]

Originally posted by sym
From an engineering point of view Steve , I'm sure you don't really believe that

. . . . surely there has to be some logical reason or physical conditions that speed their failure . . . . just what those conditions are remain a mystery.

If you think about how the MAS works in the petrol cars (I dunno if the diesels are the same) it's basically a heated wire wafting in the breeze of the air intake just after the air filter, the more air travelling into the engine the cooler the wire gets, resistance changes with temperature so a signal can be fed back to the ECU. It's a bit like a light bulb, only more controlled and not to such extremes, how can you judge why one light bulb seems to last for ages and why one will go relatively quickly? Quality of manufacture? Installation issues? I have a spot light here in the house, it only uses 40 watt bulbs but they seem to regularly pop every 3 to 4 months, personally I blame the ikea lamp unit but strictly how can it be? It's only a bit of wire with a current going through it.

In summary I stand by my original statement

S.

 

[Dieselman]

Heat!!!

It cooks the element in both the MAF and the lightbulb.

This included high output headlamp bulbs. They work by using a thinner tungsten wire but suspending it in an inert gas (xenon) so it can be run harder without oxydising.

This is why the often burn out quicker than regular bulbs.

 

[Dieselman]

Originally posted by sym
From an engineering point of view Steve , I'm sure you don't really believe that

. .

Anyway, the good news is that if it does go 'pop', I now know how to replace it at minimal cost, and without using a stealer !!!

(http://mbclub.co.uk/forums/showthread.php?s=&postid=27169)

never confirmed the part number / details on this one, but can find out very easily if anybody ever has the misfortune to need to know !!

Not happy with this! They all give different outputs at differing air mass readings.
You may save on the MAF but knacker the cat or engine.

I am fully aware of the interchangeability of MAFs but still paid for the pukka item for this reason.

 

[sym]

Thanks guys.

yes . . . true, true, but that still doesn't explain why some go quicker than . . . . . .

. . . oh . . . its really not worth losing any sleep over, is it !!!

(now you've got me worried about my headlight bulbs !!!! aaaaghhhh)

 

[sym]

Originally posted by Dieselman
Not happy with this! They all give different outputs at differing air mass readings.
You may save on the MAF but knacker the cat or engine.

I am fully aware of the interchangeability of MAFs but still paid for the pukka item for this reason.

I'm reliably informed on this one that the exchange part that can be swapped out from the vito has the identical Bosch part number to the one in the 202 on the slot in sensor part of the unit . . . so have no fear . . . they're the same !

Apparently Bosch only make about 2 parts like this for all mercs !

s.