Im a complete novice with the pico (so go easy on me! ) 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.
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
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?
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.