Hello everyone,

I have read (in this thread and elsewhere) that a rich engine can cause a plugged cat converter, plus carbon deposits in the engine. How rich does an engine have to be for it to cause this kind of problem (what lamda)? My car (85 190E, 113K miles) had a rough idle, my mechanic just made the mixture richer, plus idle higher (800 in drive on hot engine), to make it smoother. But the car is now giving me about 18-19 mpg (city driving), while it used to give me 22-23 (city) earlier. I am concerned if this rich running will ruin my cat converter and engine.

Any inputs/experiences/advice would help!

thanks,
Rags

Generally, running slightly rich will not ruin your catalytic converter but will affect your emissions.
If you are in CA, you are more likely not to pass their
exhaust emission test.
Also, you should have slightly more power.
Try a can of BG-44K, it is a potent injector cleaner which will remove carbon deposits. Our BMW dealer carries it. You should be abel to find it at certain shops but is generally not available at automotive stores. UIt is generally sold to mechanics. The cost is about $14.
Good Luck

From what Ive read and heard overly rich of fuel mixture,
will eventually ruin your cat.Unburnt fuel will pass through
piston rings and mix with your engine oil.You know whats
going to happen.Just to make sure pull your dipstick
smell it.If it smells gas,You running too rich.


Good Luck

Clauser1

thanks for the responses so far.

what rough diagnostics can one do on the quality of the exhaust (i.e., color, particles, etc.) - can that help in determining whether the car is running too rich to ignore? Also, what kind of mileage is normal for this car (190E 2.3, 85, 113K miles, normal city driving)?

Rags

You can look at the color of the spark plugs to see if they
have been for sometime since the adjustment of the fuel mixture. If it is ruuning too rich, the tips of the plugs will more on the black side. Also, your MB mechanic can check with a voltmeter, the lamba value which relates the Oxygen sensor. I have been told that the value should be between 0.6 to 1 Milli amps.
Did you check your O2 sensor, if it has been replaced??
Good Luck

Rags,

check my page (click red house) under menu item #3 for description of a Lambda tester.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

I've had the car for about 4 years, and no, I have not changed the oxygen sensor. don't know the entire history. when should it be changed?

also, i put my finger up the exhaust to see if there was substantial soot in it, and there wasn't. does that mean its not TOO rich?

Again, guys, I'm looking for some non-techy ways of detecting an abnormally rich mixture, because the fuel consumption is not THAT high - its 18-19 mpg, as compared to 22-23 mpg earlier.

Also, what does the fuel-air mixture screw adjust? someone told me its meaningless to adjust it, since the computer will turn it right back. Then why does it exist at all?

thanks again,
Rags

Rags,

Whoever told you that the air fuel adj.screw means nothing,
Hes full of it.DONT TOUCH IT.Tell you what,Put your car
in neutral or park,stand outside the car w/your right foot
in the accelator pedal and rev the engine.If you see black
smoke,your running rich.Blue,your burnig oil.

Good Luck again

Clauser

I've had the car for about 4 years, and no, I have not changed the oxygen sensor. when should it be changed?
ANS: only when the Lamda tester says it's broke!

also, i put my finger up the exhaust to see if there was substantial soot in it, and there wasn't. does that mean its not TOO rich?
ANS: NO!

Again, guys, I'm looking for some non-techy ways of detecting an abnormally rich mixture, because the fuel consumption is not THAT high - its 18-19 mpg, as compared to 22-23 mpg earlier.
ANS: There is no NON-TECHY way to determine proper mixture! Your dealing with a car not a dog! Touchy-feely doesn't work with a car!

Also, what does the fuel-air mixture screw adjust? someone told me its meaningless to adjust it, since the computer will turn it right back. Then why does it exist at all?
ANS: Give it a few turns and then watch the fun! Don't touch it without a Lambda tester AND know what to do!

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Jim, if you don't know the answer to a question, or don't want to answer it, then don't, but don't write nonsense it your replies. If you are confusing a car with a dog, its your problem, not mine.

Some people have given very useful responses to my question above, and I appreciate that.

There doesn't have to be a "techy" answer to everything. Even in a car, contrary to what Jim feels, there is this skill about being able to "feel" your way. Let me give you a specific example. Whenever I take my car (16 yrs old, 113K miles) to the local MB dealer, they adjust everything to "specs". And what does that mean? I have to go back to the dealer everytime to get things adjusted right. Many adjustments are always screwed up (idle too low, mixture too rich, etc. etc.), because what they are adjusting to is the "specs", not realizing that these specs are for new cars - 16 year old cars are all different, you cannot set all old cars to the same "specs", as each one has different wear patterns. This is where the skill and experience (the "feel") of the mechanic comes into play. In new york, I had this guy whom I used to go to everytime. you know what he used to do, each and every time? After his tech guy would be done with my car, he would take it for a drive, come back, and make some adjustments WITHOUT ANY GADGETS, just based on what he felt what the engine beat was, throttle response, etc. - and the car used to run like butter, fuel economy wonderful, etc.

Some people have that feel, some don't, so if you don't have it Jim, don't give me that crap about "touchy-feely not working in a car".

Rags

As a genral rule, they need changing about every 80,000 miles.

If your car at 113k miles has ever had an O2 sensor replacement, it is a definite candidate for one.

My dear Professor Gupta,

One thing that hasn't been mentioned is that the O2 sensor has to be hot enough for it to work. If you don't notice a _difference_ in the richness after the car gets to normal operating temperature then it's possible that the O2 sensor isn't working. Stand behind your car and take a whiff of the exhaust fumes on startup and once again when warm j/k. You might want to check out an oil test kit from blackstone labs. Unburnt fuel will foul up your catalytic converter which will cause a buildup of pressure, which will cause ignition, which will destroy the 02 sensor, which will... you get the picture. It's a self destructing loop from then on.

Kuan

PS: Is this touchy feely enough?

agupta

You DID post for help in the "TECH HELP" forum, so excuse me for providing the correct tech solution.

Maybe you should start a new forum, "NON-TECHY" with you as the moderator. Count me out!

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Jim,

its obvious from your comments that you don't have the "feel" part of it - you seem to be just like some of the people I have met who cannot think unless they have 8 different gadgets read them some output. No wonder this is what happens when you go to most dealers - they'll blabber some tech stuff and rip you out of a couple of grand, without diagnosing or understanding the real problem, which is often solvable in a couple of hundred bucks. And don't tell me that doesn't happen - I can quote you many many instances where it HAS happened. And by no means do I mean to offend the honest guys out there - I myself know one of those, so whenever feasible, I am willing to drive 500 miles to show him the car instead of the local dealer!

Anyway, thanks everyone for those who provided me some useful pointers, and there are many of those in the responses above, Jim, which you may like to learn finally.

Rags

BTW, what IS high fuel consumption? There's obviously a normal operating range for every car, but when should one get alarmed? You can't just to go a techy everytime you feel something MIGHT be wrong - is 19 mpg city driving abnormal enough to deserve diagnosis in a 85 190E 2.3, 113K miles? Nobody seems to have addressed this issue. Excuse me if this issue is not "Techy" enough, but isn't it extremely important and useful for EVERYONE who owns this car?

Mileage can vary by up to 10% depending on the season. Some states require that fuel contain a 10% ethanol mixture during the winter months. In Minnesota it's 10% ethanol fuel year round, I don't know what it's like in your part of the world. The difference between 19 and 22 mpg is about 15%. This may or may not be significant. Have you tried averaging your mileage over a month to see if these figures hold? I would try and find out if the fuel was switched for the winter, if it was, your economy problems might be solved come spring.

Kuan