P0170, P0173 Help? - Page 2 - PeachParts Mercedes-Benz Forum

dlssmith · #16 10-01-2007, 11:09 AM

Re: cleaning the MAF sensor.

Seems to be some controversy about doing that. Not that it's a big job, but how does the thing get dirty? Ok, I can answer that myself.

Maybe the better question is: why does the sensor wear out? What wears? That's a question for some one with more technical knowledge that I have...

slk230red · #17 10-01-2007, 11:35 AM

Quote:

Originally Posted by dlssmith

Re: cleaning the MAF sensor.

Seems to be some controversy about doing that. Not that it's a big job, but how does the thing get dirty? Ok, I can answer that myself.

Maybe the better question is: why does the sensor wear out? What wears? That's a question for some one with more technical knowledge that I have...

I change my air filter more often than necessary to help keep the MAF clean. When I got the P0170 code, I removed my MAF and it looked extremely clean.
So I sprayed it with CRC MAF cleaner anyway, re-installed it, cleared the codes, and the CEL hasn't returned.
Maybe someone else can answer your question of why or what wears.

dlssmith · #18 10-01-2007, 12:34 PM

Quote:

Originally Posted by slk230red

I change my air filter more often than necessary to help keep the MAF clean. When I got the P0170 code, I removed my MAF and it looked extremely clean.
So I sprayed it with CRC MAF cleaner anyway, re-installed it, cleared the codes, and the CEL hasn't returned.
Maybe someone else can answer your question of why or what wears.

I appreciate the input. I'll go ahead and clean it, nothing much to lose. I recall thinking the old MAF sensor "looked" clean too. But I'm sure the human eye is inadequate to the task of evaluation. At least mine are...

And, btw, I did replace the air filter this week too.

Arthur Dalton · #19 10-01-2007, 01:57 PM

These HFM -MAFs are more inclined to loose there accuracy/sensitivity from contaniments due to the fact that they are a Film Mass type sensors. The older/earlier LH MAFs had a Hot Wire circuit that would burn off any contaniments each time the car was turned off by a heater cleaning circuit .
So, even a thin film of smog will effect the HFM ones...air cleaner maint is a must , as is periodic cleaning of the A/F box . Performace , oil bath filters are also known enemies b/c they cause a thin oil film on the sensor..
As far as those codes are concerned , MAF is the most likely culprit, but before jumping to that comclusion, be aware that both Fuel Pressure regulator and vac leaks will cause the same , along with any unmetered air leaks. These should be check first , specially the Fuel Pressure.
The injector duration mapping on these is specific from design to operate at pre-determined pressures..and they have to be in that spec zone to work correctly. If the ECU has to adapt beyond normal limits [ rich or lean] to adapt the fuel trims for an over rich or lean condition, it will bring on those codes. Air leaks cause a lean condition and high fuel pressure will cause a rich condition..the system will correct for either only to a certain point, upon which a code will be triggered ...so, is the code telling you that the MAF is bad or is it telling you that that correction limits have been reached..........
It is not uncommon to have a fuel regulator vac hose or diapragm leak ..this allows either too high a FP or , in the case of a leaking reg diapragm, unmetered fuel getting sucked into the intake... a simple FP test and a quick look at the reg vac hose will tell the tale..and you can change the MAF until the cows come home w/o solving the problem if that is the case.

dlssmith · #20 10-01-2007, 03:05 PM

Quote:

Originally Posted by Arthur Dalton

These HFM -MAFs are more inclined to loose there accuracy/sensitivity from contaniments due to the fact that they are a Film Mass type sensors. The older/earlier LH MAFs had a Hot Wire circuit that would burn off any contaniments each time the car was turned off by a heater cleaning circuit .
So, even a thin film of smog will effect the HFM ones...air cleaner maint is a must , as is periodic cleaning of the A/F box . Performace , oil bath filters are also known enemies b/c they cause a thin oil film on the sensor..
As far as those codes are concerned , MAF is the most likely culprit, but before jumping to that comclusion, be aware that both Fuel Pressure regulator and vac leaks will cause the same , along with any unmetered air leaks. These should be check first , specially the Fuel Pressure.
The injector duration mapping on these is specific from design to operate at pre-determined pressures..and they have to be in that spec zone to work correctly. If the ECU has to adapt beyond normal limits [ rich or lean] to adapt the fuel trims for an over rich or lean condition, it will bring on those codes. Air leaks cause a lean condition and high fuel pressure will cause a rich condition..the system will correct for either only to a certain point, upon which a code will be triggered ...so, is the code telling you that the MAF is bad or is it telling you that that correction limits have been reached..........
It is not uncommon to have a fuel regulator vac hose or diapragm leak ..this allows either too high a FP or , in the case of a leaking reg diapragm, unmetered fuel getting sucked into the intake... a simple FP test and a quick look at the reg vac hose will tell the tale..and you can change the MAF until the cows come home w/o solving the problem if that is the case.

This is good information. It really helps me to understand what might be going on. At least it will give me proper ammunition to better know what questions to ask the technicians.

Many thanks.