Mercedes-Benz Forum banner

MAF question?

4K views 25 replies 9 participants last post by  Kajtek1 
#1 · (Edited)
Does running the car with the MAF disconnected cause any harm -- I'm reading this is a way to test them? I have never had any luck cleaning them?

I'm having an issue with my 01 W203. Same basic motor as the W210

The car has had two episodes of running rough over the past few years. Both times came up with #2 cylinder (or that bank) and both times I had a bit of oil on the cables. It was a tiny amount and really only on one cable. I never could see where the oil was coming from and quite frankly was surprised that it would cause a problem.

Last week my sister drove down (mostly highway) to another relative (1.5 hours) and when she went to leave about 1/2 hour later it would not idle. I drive down and naturally it starts and runs fine - no codes -- shut it off and check all the cables and coils on the passenger side -- all fine and dry. Drive car home and figure I would replace that one cable that had been wet with oil ...thinking maybe something is up.

So the other day after driving at highway speeds for about 3 hours -- it will not run. Very rough -- car will not go over 15mph .. we limp it home .. CEL started to flash.

I pull codes (10) and all point to misfire on passenger bank cylinders and also P0170 an P0173 They have to do with fuel trim and many say bad MAF. Clear and recheck. It has to run for a while then I get some missing and it comes up Cyl 1 and 2.

I just don't see how I could have two coil problems or plug wire problem -- if it runs fine sometimes? It will run at 3000RPM fine.

The car will be due for its plugs (100k) and I can certainly get a set of cables and the Bosch MAF is only $140. But what else would cause a stutter off idle like this with no codes -- until the car is really running badly. I would think fuel pump would not let car run at 3000rpm?

I got a check alternator/ battery warning at one point -- but I know this was because it was almost at a stall -- can rough running cause P170/ P0173?

I replaced the CPS last year... real pain on this one
 
See less See more
#2 ·
The C is tighter under the hood, and there is anecdotal evidence, perhaps based on that, that it tends to cook ignition wires more quickly than the V engine in the E and S chassis.

So I'd plan on wires when you do plugs.

The flashing CEL is a major misfire detection. That could be caused by a few things, including a failing (or dirty) MAF.

My suggestion would be to clean the MAF per the DIY at the time you change the plugs and wires.

If the codes recur, I would then swap the MAF insert between the cars. (If the assembly is the same, just swap the assembly, but I don't think they are.)

That's the benefit of owning two, you have a temp/testing donor. ;)

If that takes care of it, then you know to replace the MAF.

And yes, there are some other possibilities, but that's how I would start. Easiest and least expensive.

Good luck.
 
#3 · (Edited)
Thanks -- I was not driving it when it was flashing. The driver said -- this light was flashing and it would not move ... one of those stories.

My wagon is at the shop -- got hit two weeks ago and now looks like trans damage ... so I don't have the car to switch the MAF.


I guess you don't know anything about the running without it connected trick? It is not something I have heard of.


I will give the MAF a cleaning -- although I have never had it work.
 
#4 · (Edited)
The car will run but...

Disconnecting the MAF will cause the ECU to use a default value and run too rich a mixture. Besides wasting gas, the cats will be overloaded with excess gas overheat and eventually burn out.

Note the MAF sensor must be removed from the housing to properly clean the element. I clean mine once a year or at each air filter change which ever comes first.

FYI - MAF's are sized based on engine displacement so unless your W201 is 3.2 l it will be the wrong size. Although it may well fit in the housing.
 
#5 ·
Of course you can always replace parts blindly in the hope that that will fix your problems, and ultimately this road might even lead to success. But a set of OEM ignition cables costs more than $100, while testing each of them for resistance with a multimeter costs perhaps 10 minutes of your time--especially if you take them off anyway when replacing the spark plugs. If you measure a resistance in the range of 2kΩ you know that they are fine. If you find one or more that are off range, you can still replace these individual wires, which cost about $10 a piece.
 
#6 ·
It is the same MAF sensor (insert) for the 2.4 and the 3.2 (same part number for C240 & C320).

There are many threads about disconnecting the MAF, and I've weighed in on many of them.

Remember that in these engines the MAF is also the IAT sensor. So when you disconnect it you are, as Richard notes, forcing it to run in default mode. You never want to do that for any extended period. While in some circumstances this can be useful as a diagnostic tool, in most cases running in default can then mask other issues, so you may end up replacing a MAF and then still have the problem.

If I thought it had any value for you, yeldogt, I would have suggested that you go ahead and try it. At this point, I think it is better to focus on due/deferred maintenance items, and then see where you are.

Call the shop and see if they'll let you pull the MAF. If it's not going anywhere, them moving it around the shop won't hurt anything.

Alternatively, buy a MAF. If it isn't needed, with two of them you know you'll need it for one or the other sooner or later. ;)

Good luck.
 
#7 ·
What mileage ? If it's over 125K - if you are planning to keep the W203 - then I would invest in a fresh Bosch MAF.

Yes - misfires like you describe - with increasing frequnecy - "normally can be traced to a MAF.

For $35 more order a fresh Mann/Bosch fuel filter + buy a $9 bottle of Stabil marine Formula (you will use 1/2 bottle 1 application) - for intake cleanup.

Fresh Mann air filter + MAF for intake cleanup.

Overall - this will maximize your efficiency and fuel economy on fuel + air intake.

If problems then continue to occur that's when you pull/swap wires and coil packs + if over 125K get into OE spark plug change..
 
#8 ·
Thanks everyone.

The car would not run with the MAF disconnected .. so I gave it a clean and reinstalled .. no difference. The car runs fine until I try and raise the RPM's and then it stumbles. I'm not getting any codes . I'm sure if I let it cough and sputter for 10 min I will get one of the passenger bank cylinders to pop up .. as yesterday #1-3

While I'm not one to throw parts at cars in the hope of fixing them. At almost 100k I would be doing some of this anyway. I have a full set of the Bosch 9652's in the garage .. and with amazon prime I can have the Bosch MAF and Bosch 09848 plug wires at the house on Tuesday for $240. I normally replace the wires with the plugs anyway -- and the MAF is a known issue ... so If it's not the problem I will have a spare. I'm going to order a fuel filter also.
 
#9 ·
I heard lot of stories about MAF.
Evidently some engines run with them disconnected, some will not.
I had bad MAF failure in VW and after few seconds of hesitation after start, it would switch to default and run with about 80% of normal power.
MAF failure on 320 MB I had would choke the engine, but not switch to default.
I have seen MAF testing procedure in W163 section, but it was not easy one.
 
#10 ·
Update: Started putting parts on yesterday morning -- car fired up with new MAF. Still rough .. I replaced the spark plugs and wires on the passenger bank .. better. The plugs were in wet, not original and worn .. bit of a surprise. The car was still not running correctly -- I could feel something off. Now able to drive to my local shop -- weak fuel pump.... then dead fuel pump. So new fuel pump going in today as well as the fuel filter I got with my order.

If this is the end of it ... more than likely the issue leaving the car stranded twice recently .. was the intermittent pump. That would explain the 1st stranding without codes, and being able to drive it 100 miles home. I had the plug wire problem on #1 and #3 .. it is hard to say if the earlier codes were a border line MAF .. or the pump all along.

Will switch out the other bank of plugs/ wires in the next week or so. I may have wasted $120 bucks on the MAF. But its done ...

Between business and personal I have 12-15 cars at any given point and have for the past 30 years .... in all those years I have replaced a fuel pump in every german car I have owned .. and none in all the rest. Same with the MAF -- I have no idea what a Japanese MAF looks like!
 
#12 ·
My 02 wagon needed one at around 120k (summer of 13) this one is just under 100k ... did a couple in my SL overt the years .. let's not talk about my W140 ... have had a bunch more MB's. Lexus, Nissan, Toyota .... Large number of Ford built vehicles ... we never get rid of them early .. many of the Lexus vehicles went well over 200k to 250k.

Fuel Pump Update: The fuel pump cost for the W203 is a bit of a disaster -- mine is an early car. They no longer make the pump assembly -- it is superseded by another pump that requires the sender (the tank is under the back seat and wraps around the driveshaft) The sender is $500.00 + plus the $300 + pump ... so I'm looking at $1500.00 for the fix. MB strikes again.
 
#16 · (Edited)
In modern cars there less and less space for straight tank, so the manufactures make complicated shape, that not always will drain from single hole in the bottom.
W211 gained lot of trunks space comparing to W210 thanks to squeezing the tank under the floor.
In case of sedan, the tank over driveshaft makes 2 separate lower bowls, while in M class the wedge-shaped tank has no option to install pump in the lowest point.
That forces a design, that while electric pump sucks fuel from one part, the returning fuel powers Venturi pump that sucks fuel from other part into the pump compartment.
The design works well if done well, but small misalignment in assembly and Venturi pump gets messed up, making part of the fuel unusable.
Drop in quality of MB parts is another story.
I had electrical connector on the pump in ML burned out.
Since there is no oxygen in the tank, the electric fire did not blew the car up, but sure makes nice headlines.
 
#15 ·
I do have a question for you yeldogt, you mentioned the plugs were "wet" can you describe what kind of wet? There are two, oily wet, or, a dark even carbon color wet, which is clean but carbon color and wet, and doesn't change when wiping it with a rag/cloth (has little to no soft carbon or oil deposits or residue) or the deposits left behind when you pass a cloth over it? The second type of wet dries quickly with a match!
If you aren't sure, what you can do is run the the engine for 15 minutes, wait 30 minutes for it to cool, and pull a couple of the new plugs from know cylinders that were wet!!
let us know
Patch
 
#19 ·
So the reason I asked is, likely the injectors are leaking! Given what you are doing, and I've been there; take the opportunity to send them out for service. You will be more than pleased with the new overall performance and sure starts, hot or cold. Leaving in leaking injectors leads to a rapid shorting of the engine life.
As you are the mechanic, all you will have to pay out is the 20ish $$ per unit for the process, do not attempt to clean them your self.
Remember to clean the injector area very, very well before removing them.
Patch
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top