M103 Running Rich
 

Hi All,

So my m103 is running a bit rich. You can tell at the exhaust, its pretty strong!

I am trying to think of all the places that might be causing this behavior.

1) Lambda Tower setting
2) EHA
3) EHA Control Issue
4) Oxygen sensor

A few months ago I replaced all the rubber above the intake manifold as well as the fuel injectors and seals.

I believe I set the lambda tower so that the duty cycle at the X11 port read 45-50% or so.

Just starting a discussion on the topic. I've not had a chance to do any investigating yet. I still manage to get 23-24 MPG while driving 75-85 MPH on my commute.

--Kris

Tune up parts? When was the last time you did plugs/wires/cap/rotor? I'd pull a plug or two first and see what they're like.
After that I'd figure oxygen sensor. How many miles are on that?
Personally I'd say 23-24 is pretty darn good especially if you're doing 80 on the highway a lot and the way the m103 revs high at speed. I'm lucky to crack 20 with new york driving lol. Unless you're used to getting better than that with your car.
Also the green 2-pole temperature sensor at the rear of the head, maybe give it a test?
Unless your cat converter isnt really scrubbing anymore and making the exhaust smell rich. I doubt that though theyre pretty tough.

Tune up parts I think are OK, long as my intervals are set accordingly.

https://photos.smugmug.com/photos/i-...8bLgbTV-X2.png


Fuel Econ wise I think its where it has always been, long back as far as I started tracking it:

https://photos.smugmug.com/photos/i-...-nJSLKTK-L.png

I should pull a few plugs and see what they look like.

I know that the smell is pretty strong for the most part. I don't have a cat on this car anymore. The original was removed a long time ago. A replacement was fitted but it was killed by the excessive amount of fuel. (according to the exhaust shop). Its straight piped while I try to figure out whats wrong.

ehhh...
23-24 mpg in my opinion is too good for it to be running rich, especially rich enough to kill a cat converter. What kind of cat was put on the car that failed? Probably some type of aftermarket and not oem benz. Without a cat on there the raw exhaust is gonna smell way more gassy than if the cat was on anyway. I would think that if it was running rich enough to melt the cat you would be getting single digit mpg. Also the cat would probably get so hot it would glow trying to burn off the extra gas and your carpet would melt lol (I've actually heard of this happening).

You believe you set the duty cycle, but I would say check it to see what its actually doing.

I envy you. For years I've seen 20 mpg at 60mph-65mph. Like another respondent above in this thread, I'm at a loss for how you are getting that kind of mpg at the speeds you report from a barge that runs a high revving motor?.

I've been using the same measurement/calculation technique on all my fill-ups. My commute is about 128 miles, I can get two days out of the tank, roughly 11-12 gallons.

Maybe the difference is in lowered W201 vs W126?

The cat was aftermarket. I am not so convinced that the cat was killed by emissions/fuel as much as it may have been by physical/mechanical impact. The 190E is lowered and I am just wondering if I hit something with it and just don't recall. I brought it to the exhaust shop because of a rattling noise I would hear on startup (and for a bit after that).

The whole exhaust is aftermarket, ending with a magnaflow dtm style muffler.

But it does run rich, you can smell it easily.

Next time I am running it I'll probe X11 and see where duty cycle actually is. Its parked for now, not too great in the snow with its current tires and the fact that its lowered.

For what it's worth, my SL is straight K-jet (no emissions controls) and no cat (Euro model). On startup, you can definitely smell gas when the cold-start injector is open. I run it on the lean side, and when warmed up, you can still faintly smell gas. Still get in the mid-20s on the road though. It could just be that without the cat, you smell the fuel.

I'd be leaning more towards a defective cat than anything else. My dad's 2012 F-150 3.7L V6 had a really irritating rattle. Took it to the stealership and the driver's side cat was damaged (broken away internally). Truck still under warranty, 13K miles on the clock.

The m103 can achieve almost 28-29 mpg when cruising on the freeway. In that smaller body, I can imagine you could* get 30mpg.

Start with fresh plugs and work your way back. I'd avoid tampering with lambda adjustments as you are running in closed loop.