[Billy22Bob]

Trying to find the characteristic curve for the 0280217114 MAF used in the SLK230.
This is the Volts output for a specific kg/hr throughput.

I've got the bosch HFM2 and HFM5 spec sheets (attached) but cant get it nailed with the same PN#
It looks like a HFM5, but I cant match the dimensions exactly.
I can find a HFM2 as a 0280217120 and the dimensions all check out, but its not a 0280217114.

Anyone who's been down this road before - advice/help appreciated.

 

[stelios109]

Thats a point Im trying to figure out for a long time. I ve only found the sheet that you attach. Guessing on how the codes go, the -114 code should be very close to -120 code and curve #2. Main differences between codes as you see, are not the sensor itself but secondary dimensions in the housing. Of course these dimensions are critical on how quick the sensor cools (thats a reading) depending of the possible air mass passing. (D and H dimensions)
My other thought, is to stick voltmeter and test on run, not on idle, to avoid bypass open, and at the same time, check the live data and ecu's maf read. If the range of low and high value and 1-2 values in middle volts is according to that graph, then they match.

 

[Billy22Bob]

My other thought, is to stick voltmeter and test on run, not on idle, to avoid bypass open, and at the same time, check the live data and ecu's maf read. If the range of low and high value and 1-2 values in middle volts is according to that graph, then they match.

Would be good to get the chart. I noted that this is only Pages 55=57 of some larger Bosch document. There might be others on pages 0-55...?

Not sure what you mean about "test on run, not on idle, to avoid bypass open". Surely everything goes through the MAF for your fuel algorithms.
I cant recall - is g/sec air shown up on the OBDII live data? I don't have a logger.

 

[stelios109]

Would be good to get the chart. I noted that this is only Pages 55=57 of some larger Bosch document. There might be others on pages 0-55...?

Yes probably, but I think other pages should be other Bosch products.

Not sure what you mean about "test on run, not on idle, to avoid bypass open". Surely everything goes through the MAF for your fuel algorithms.
I cant recall - is g/sec air shown up on the OBDII live data? I don't have a logger.

Sorry, I meant to read the volts on car moving. My logger gives g/s, but whatever the OBD sends can be converted to another unit, I dont know if it is software feature or the initial signal from OBD.
If we look to -120 code gives max 480 kg/h, that is 133 g/s. Here's another question. I ve read up to 120 g/s, so Im in range. Some weeks ago in another thread users wrote above 133 g/s. I think it was user dandywarhol with prefacelift, not sure. So, is the max 133 or the -120 code has different range?

 

[Billy22Bob]

sounds about right....
using 478.8kg/hr = 133g/s

if you use the old 150hp/100cfm rule
133g/s at STP (25C+101kPa) gives you 236cfm = that'd gives you 160bhp or 120kW.
That's in range.
Some run these 230's upto 170kW 220bhp without either reporting or knowing if the MAF is reading incorrectly at the requisite 183g/s (660kg/hr).

I guess they're still working ok but someone may have reported a problem elsewhere....??

 

[Billy22Bob]

Okay - work around - waiting to be confirmed

It would be good to do the multi meter thing to confirm the following.....

1. I confirmed the terminal on one end (the rounded socket end) is terminal 5 and is the "spare" temperature resistor (RTD). The centre pin I also confirmed as the Earth post.
Then I confirmed it matched the 2.20kOhm output with the spec sheet and the temperature at the time of 22.7C. I formulated a plot for 10-50degC and worked out a reverse engineering formula (solution) that - given a kOhm output I can work out a degC.

2. I had a bit of think. I figured the HFM-5's* "may" all use the same element, and the element is simply influenced (as a very rough assumption) by the velocity through the throat/venturi.
So I analysed the kg/hr, worked out m3/s and then divided by the throat m2 to get m/s throat velocity. I then read off the Volts at 100, 300 and 48kg/hr for each of the 5 curves. Then I plotted velocity versus Volts output and voila....a reasonable fit.

I've attached my rough calc sheet - for anyone interested.

Measuring our throat at 60mm ID, I'm thinking we are closest to Curve 1, however it tails out at <400kg/hr and so I think that's why it has the 130mm length - to afford some more flow straightening.

Anyway - I'm going to move on and work with this until a better curve pops up. I'll hook up my spare to 14V battery and a pitot tube flow bench setup and see what comes out.

*(note - ours is called a HFM5-4.7 by maf-shop.com and I've emailed them for a chart)

 

[stelios109]

Some run these 230's upto 170kW 220bhp without either reporting or knowing if the MAF is reading incorrectly at the requisite 183g/s (660kg/hr).

I guess they're still working ok but someone may have reported a problem elsewhere....??

Im also in this setup, revving supercharger up to ~14500rpm, but I havent clamped my MAF, so it hits the maximum volts, as it should be. Nevertheless, there are no CELs, the car performs good in all rpm range, LTFT, STFT, O2 Volts are ok. Guessing, the safety gap of ecu, gives room to increase air up to 25%-30% more than stock. But for sure there is a problem with the MAF's signal and the real air mass at top end.

2. I had a bit of think. I figured the HFM-5's* "may" all use the same element, and the element is simply influenced (as a very rough assumption) by the velocity through the throat/venturi.
So I analysed the kg/hr, worked out m3/s and then divided by the throat m2 to get m/s throat velocity. I then read off the Volts at 100, 300 and 48kg/hr for each of the 5 curves. Then I plotted velocity versus Volts output and voila....a reasonable fit.

Good catch, venturi is the key.

 

[dandywarhol]

You could try the Pierburg website for further info. The Pierburg MAF insert I used is a 7.22684.09.0 which is argueably a better unit that the Bosch as it doesn't tend to get the oil mist problems due to a different design

 

[Billy22Bob]

and a direct replacement?
You are obviously happy dandy.

 

[dandywarhol]

Direct replacement. And you only have to get the insert.
No problem since fitting it in April

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