Mercedes E300TD (W210) Maf Sensor Faulty?

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Mercedes E300TD (W210) Maf Sensor Faulty?

Postby tim44 » Tue Jun 19, 2012 1:56 pm

clean maf and af 3.psdata
E300td (W210) Maf sensor - sensor signal.
(212.73 KiB) Downloaded 293 times


Hi everyone

Im a complete novice with the pico (so go easy on me! :wink: ) but I got a lend of one last night to check my maf sensor.

I have an old E300td (1999) that is in need of a lot of work. Among other problems I suspect the maf may be faulty and may be contributing to the car being down on power at times. (The vehicle is suffering from various faults that would also cause a low-power condition but I just want to check the maf too before buying one!)

I first checked the air filter and found it to be black so it was replaced. I took some readings with the scope pre air-filter change and post air-filter change. They were exactly the same.

I was hoping someone could take a look to at the post-air-filter-replacement waveform (attached) and see if they spot anything meaningful. The main problem I can see is that its only ranging between approx. 1.5v - 2.45v.

I cannot find a wiring diagram for the engine management on the e300td (om606.962) but basically in this capture I had the scope backprobing the maf signal wire and maf earth wire. (in previous waveforms I took last night I hooked it up between maf signal and an external earth - the waveform was the same, just a bit more 'hash' on the waveform).

The waveform shows the engine at idle, then wide-open throttle, then back to idle.

Id really appreciate any observations you may have on the waveform.

many thanks
tim44
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Re: Mercedes E300TD (W210) Maf Sensor Faulty?

Postby Liteace » Tue Jun 19, 2012 6:55 pm

Check the connecting plug you should have:

pin 1, intake air temp
pin 2 , 12 volts
pin 3, ground
pin 4, 5 volts
pin 5, measurement signal

If you have a good 5 volts on pin 4 and your only seeing 2.4 volts on pin 5 at WOT I would say you need a new MAF, you should be seeing 4.0 - 4.5 volts
DONT SHOOT YOURSELF IN THE FOOT
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Re: Mercedes E300TD (W210) Maf Sensor Faulty?

Postby tim44 » Wed Jun 20, 2012 7:59 am

Hi Liteace

As I didnt have a wiring diagram I just back-probed each pin to figure out which was which. All other pins are giving correct readings, feeds and earths are good etc. so I'll just order a new MAF. I also checked last night for any leaks after the MAF which may cause a low peak reading but everything was ok. Once new MAF arrives I'll post a new 'good' waveform in case it's useful to anyone in future.

May I ask were you able to get a wiring diagram or pin info?

Thanks for your help.
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Re: Mercedes E300TD (W210) Maf Sensor Faulty?

Postby Robski » Wed Jun 20, 2012 11:17 am

what if it's still low after a new MAF ?

Are you 100 % sure you have checked everything that can cause a low MAF value ??
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Re: Mercedes E300TD (W210) Maf Sensor Faulty?

Postby tim44 » Sat Jun 23, 2012 1:45 pm

Hi Robski

I dont have a huge amount of time to spend on the merc at the minute so I cant be sure that I have eliminated all possible causes of low maf reading, e.g EGR etc. I got an ultra cheap second-hand tested genuine maf sensor. It arrived yesterday. Even if its not a faulty maf giving me the low readings it'll be handy to have a spare for all it cost. Ill have more time to investigate next week so will report findings and results.

To the members who pm'd me, as Im only a new member I am unable to reply to pm's. Sorry.
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Re: Mercedes E300TD (W210) Maf Sensor Faulty?

Postby Martyn » Mon Jun 25, 2012 7:23 am

Should be able to reply to pm's now :)
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