I've been getting some CEL codes about vacuum and fuel trim issues. Not always, but often this is due to a a dirty/loose MAF or other intake issue. So I took apart the intake system and all looked well, no cracked hoses and so on, except that I noticed there's no clamp where the MAF housing meets the throttle body. Now the way the MAF housing clips on the blocks, its fairly snug on there. But, this engine has considerable intake pressure at WOT, so I'm wondering if that connection is leaking. Is there suppose to be a ring clamp of some sort?

I'm also going to throw in some injector clean over the next tank or two. I'm not to worried as there's no sputtering or serious low fuel issues, like audible knocking under WOT, etc.

(from memory, I think the CELs were P0171/P0173/P0450)

any thoughts?

thanks,
chrismon

 

My C200 has a ring clamp on each side of the MAF.
Shan.

 

Hi,
I guess your 320 has a 112 V6 motor in it.

IF your codes are reported correctly then this may help.
P0171 Fuel Trim Lean Bank 1 /P0173 Fuel Trim Malfunction Bank 2
P0450 Eval Loss system pressure sensor
The fuel trim problems point to a faulty MAF or intake leak.
The evap loss points to a tubing leak or as it states a sensor malfunction. I guess these are different issues.

If a 112 the MAF housing is not secured in place other than by a special sort of plastic clip.
The engine side of the housing plugs into the inlet manifold using a special flanged rubber O ring which needs to be correctly seated due to some protruberances on it.
The MAF body is then "loosely" retained by the special plastic clip which goes around the body and engages in two places with lugs on the manifold.
The assembly is not held rigidly and can sort of move around a little until the aircleaner is pushed on which then constrains the whole thing adequately. Ensure air cleaner/inlet box gasket is also in place.
Not sure what your air cleaner box looks like becaus ethis changes model to model.
Both sides of the MAF body need to form effective air tight seals.

There should be no "significant" pressure on the inlet side of the MAF since this is not a "Kompressor" model. If there is where is it coming from.

How do you know it is there on WOT?

The post referring to ring clamps on a C200 is I believe a 4 cyl 2000 Kompressor which is totally different set up.

Hope this helps.

Stuart

 

Thanks for the reply. Yes, its the V6. Thanks for the code descriptions though I had already seen them with my reader... I was typing in the post from memory That MAF certainly looks pristine, though I can only see that outer element that looks a bit like a diode (black/copper-looking glass blob on a wire) and I'm guessing that's just a temp sensor. I'm betting there's another sensor inside the MAF unit which is the actual mass sensor - no idea how a can of cleaner will get to that, but I suppose I could soak it with some CFC. I suppose I'll take another look at the intake and other tubing. There's that
valvecover-to-throttlebody tube which I've read is notorious for cracking. From visual inspection it looked OK, but I think I'll crack the obnoxious plastic cover back off.

Where is the evap pressure sensor located on the 112?

Thanks for the info about the 112's MAF housing. At least I know I don't have to worry about it.

This C320 was a gift (sort of) from my wife's side of the family and its a nice car, but expensive to maintain. I do not want to pay for a new MAF, so its the last resort.

 

Hi,
Dont soak the MAF sensor. The seal to the electronics inside the sensor body absorbs the agent, swells and ruins the seal.
Spray it by all means and quickly blow dry.
Some cleaners work others don't.
I use Toluene but I guess there are many proprietrary carb cleaners that may work.
Not all MAF sensors respond to cleaning. depends if sensor is dirty or damaged.
Little blob is indeed the temperature sensor. The airflow sensor itself is a thin film on a substrate that runs back into the elctronics box on the snesor body.
The fact that you have a 0173 - Malfunction suggests that you may need a new MAF sensor.
Can get them quite cheaply on eBay.
Best to use OE Bosch but Pierburg and others make them.
Check you get the correct one. Many look the same but have different characteristics to match the engine type / fuel.
No need to get the MAF body, just the sensor so long as you have a security torx socket to unscrew the sensor.
Changing the sensor will be worth it.
Just don't pay MB prices (or labour) for anything unless it is your last resort.
Chaning the sensor is a 5 min job.

The hose you refer to connects the engine breathing system to the aircleaner/inlet. Important this is not damaged since it upsets a lot of things.

Don't know where the Evap sensor is. Would need to follow the lines from the tank to the CharCan (charcoal cannister). Giess it will have some leads going to it. Could be on LH inner fender / strut spring panel.

Stuart