Bernanke

hey guys,

well now that i fixed the fuel pressure regulator i was wondering if maybe my mass air flow sensor is bad. I believe it is still the original one with the car (which is nearly 13 years old), is there a possibility that it is almost dead and thats what is causing the poor performance on my car? The FPR definitely helped idle and etc but i feel as if the throttle responce is not very precise making me think its mass airflow related. what do yall think?

brett san diego

What year is your car? 1996 or later will be OBDII compliant, and you can hook up an OBDII scanner that will read sensor values in real-time. Read the air flow measurement and compare it to factory specs. The more difficult part could be finding the factory specs. If I recall what I have read correctly, MAF sensors will usually underestimate actual air flow when they start to go south, so your car will be running lean.

Brett

c55m8o

only one reply ... ? geez, this board...

I've discovered there's "levels" of MAF failure.

Starts as general "sluggishness" ; as if the car was 1000 lbs heavier ; with a lack of responsiveness to subtle movements of the right foot. Most notable between 1K - 3K RPM and light acceleration. I surmise that is because when the throttle is hardly cracked and you need the highest sensitivity of the mass air flow sensor ; thus the car is more likely to surge with a bad MAF. It also affects the transmission shifing; I think they call it "flaring".

Extreme case is what I had after I cleaned and oiled my K&Ns when I swapped my motor. Carl (coolcarlski43) said after he saw the amount of oil (which I didn't think was excessive at all), "oh man, you're going to ruin your MAF". Sure enough, a few months & few 1000 miles later it started with problems starting the car. It would actually stall after the initial startup. Could take up to 10 tries before the eingine would stay running. Later, if I'd some to a stop light within a few minutes after starting the car, if would stall; but only when cold. Then I was even getting cases where the tranni would get stuck in 2nd and not up or down shift (scarry). Finally, I got a check engine light after one trip into NYC where it stalled twice when hot (never happened before).

So I called the guy that did my motor swap. Now for the quanititative analysis. The bad news is that the Mercedes Star Diagnosis Computer -- this guy owns his own -- screen that actually measures the MAF (the one that displays the amount of fuel injector "adaptation") is very likely to stay "within spec" even with a shot MAF (as it did for me). Your allowed 1.36 (or there abouts) milliseconds of injector adaptation. Mine was at about 0.94 ... my mechanic was surprised, but he knew better. (he did read a "Hot-Wire Mass Air Sensor" code too.)

So then he went to another panel that did realtime scanning of the amount of air metered. At idle it is supposed to read 16Kg/hr. Mine was 12. Further, when he'd rev the engine, the reading never when over 100. He said it should be much higher.

After putting in the new MAF, idle was spot on @ 16kg/hr, and reving I saw readings of something like 648 kg/hr. Woe.

Result? most noticible was responsiveness off idle ; the car no longer felt like it was pulling through muck between 1K - 3K or was 1000 lb heavier. And further, it pulled nicely up to redline now, where before the engine torque would really trail off before the shift, and then push you back into the seat after the shift. Now it not only shifts more smoothly, but also pulls much more evenly up to redline, so there's obviously not as much fall-off in torque up at the topend.

I'm just so sorry I waited to song the change mine; in retrospect I probably could have used one 30K or 40K miles ago. The car acts like it used to now when it was new ... thank goodness for that... (but now with the bigger & badder motor... )

brett san diego

So c55m8o, did you try cleaning the MAF sensor first before giving in to replacement? I know this has worked for some, but results seem to be spotty.

Brett

Bernanke

thanks for the posts guys. I cleaned my HFM with alcohol once before and it definitely helped but over time its gotten bad again (i think i may have a real K&N replacement filter in the actual Ractive intake unit). I may have to clean my MAF.

the thing that is weird about mine is that from 1-3k rpm my car pulls the hardest, and it starts having problems on the top end which is kinda weird. thats what i dont understand.

c55m8o

Yes. About 30K miles ago. It did indeed help a bit (from the time I mussed it up the 1st time after installing the K&Ns). But it was no where near the result I got in engine responsiveness that I got after putting in a new one.

bigintruder

Brett, I own a 1995 S600. Based on your reply above, am I to assume that my car would need an OBDI scanner? If so, how do you get to the scanner plug on my car?

pcmaher

You really should see if there are any stored fault codes. That will help point you in the right direction.

http://v12uberalles.com/pulling_codes.htm