Hi

I cleaned my Sensor and all appeared well, but when I had some work done on non starting and it proved to be out of spec. A new genuine sensor has made car run much better.

It wants taking off and cleaning, do not touch the sensor - worth a try before you purchase.

The MB service does say replace at intervals?

 

I think Murat is talking about the map (the little thing with the small hole)

similar to this one.

Tapatalking

 

I am not familiar with the 200k at all but on other 170 the MAP is only used during starting. Once the car starts, and starts calculating LTFT, the MAF takes over. So I would start by looking for leaks elsewhere- downstream of the MAF.

Injector seals are a common culprit, along with manifold gaskets

 

thanks efair, I think the story is different on a supercharged engine as it has 2 pressure sensors one for atmosphere and one for inside of the manifold (it is boosted over 1 atm when kompressor pressurizes). Also boost pressure on obd shows 0,2 psi with the engine off. I think it should read zero meaning outside and inside are equal when engine is not running.

 

You need to reset mixture adaptation and see if rich condition is coming back.

 

I got told by the garage that you couldn't clean the MAF.

But I already knew I could from all the info on this forum (and the vid in an earlier post).

The key is not too touch it, and to use the correct solvent.

 

Just watched the MAF video and it brought this to mind ...

I recall asking about the MAF on the SLK230K as it was listed as a "potential trouble spot due to being contaminated with oil, and quite expensive to replace" in one of the consumer report/evaluations of the car. According to the shop, the oil comes from a cylinder head breather/oil separator... something about a gasket or o-ring on the separator that fails and allows oil to pass into the intake system.

'You prevent contamination of the MAF by checking and replacing that gasket when it's worn. I check them on every service (only takes a minute) and replace the gasket when worn (it only costs a few dollars) as a standard service item.'

So: If you take an MAF out to clean it and find oil in there, you should clean out the oil in the tubes connecting it and check the cylinder head breather system for worn gaskets/leaks.

G

 

Murat,
Ah - I see. I still cant answer your question, and I don't have a 170 to compare for you.

I wonder what the ECU does with the MAP readings from the manifold. I would think the mass of air entering would increase when the supercharger is boosting, due to the density increase, and the MAF would detect and adjust.

If you suspect your fuel trim is biased by a faulty MAP sensor, and you feel letting the ECU adjust is unacceptable - replace it.

Keep us posted!

 

yesterday after work, I tried to spray some contact cleaner into the tiny hole of the MAP. No changes...Then, I swapped the BARO sensor with the MAP (actually they have the same part#) the LTFT got even worse...-6%. Although the ecu compansates that and there is no CEL. I'm sure I have got a sensor soon will fail, or two. :surprise:

I think the way to check the sensors is connecting them as Baro sensors and reading the values and comparing with weather forecast. So I hooked the car to an OBD scanner and was able to read the BARO value as 1048hPA which should be around 1017 at sea level. Checked and confirmed that also from weather fcst and it was 1016 for where I live yesterday. So I have high reading on at least one sensor. I have to swap and read the other sensor as well, but taking the MAP out is a big PITA. I plan to do it by the weekend and will order an OEM sensor meanwhile.

I have no idea about the correlation between MAF and MAP, but I cannot not find a meaning full explanation to my negative LTFT other than than this MAP issue. Ive already changed the MAF, plugs, fuel regualtor and the O2 sensor. The injectors were also checked for leak and equal fuel delivery.

Will keep you informed after solving that MAP issue.

 

Okay, just replaced both MAP and BARO with 005 153 7228 (updated part no) engine runs smoother and LTFT is now around -0,5%.
Certainly, both were faulty and reading high. New baro reading is exactly the same as my iphone's (By the way, I always wondered why apple puts a barometer in iphones)