lean mixture - PeachParts Mercedes-Benz Forum

andrew1413 · #1 05-17-2004, 01:31 PM

Do I understand right that a lean mixture (O2 Lambda Sensor < 0.45 Volt) represents low fuel and high oxygen level and that results in complete burning of all fuel and low CO and HC on emission test?
Another word, can I change a mixture to lean via regulator on the air filter to pass an emission test? I understand that a car will lose in power because of a lean mixture but will it reduce CO and HC in exhaust?
Txs.

EricSilver · #2 05-17-2004, 04:01 PM

Yes.

I did it about two years ago when I was concerned about emmissions testing, even though it was not necessary. My numbers -- CO, NO, HC -- were almost unbelievably low. (I also never got around to adjusting my mixture back and have been running lean ever since. Could be the cause of my sometimes sluggish acceleration on the first drives of the day.)

If you are having emmissions problems now, you might want to figure out where the problem is, beginning with leaky injector seals (a quick and easy DIY job if you have the right wrench) and your O2 sensor.

Also, the 260 needs to be hot in order to pass (at least on the first try) so drive around town and run all your errands before the test.

EricSilver · #3 05-17-2004, 04:05 PM

I should add:

You are not experiencing a complete buring of fuel by running lean. You are simply burning too little fuel to cause enough bad emissions to fail the test.

The test measures the net volume of CO/NO/HC produced, not relative percentages of fuel burned to "dirty" emmissions. Your emmissions problem, if there is one, will still be present, but of a lesser magnitude.

andrew1413 · #4 05-17-2004, 04:44 PM

I do have a leak in front right side of the engine. But I do not know where it is comming from.

What should I do to fix leaky injector seals?

jbaj007 · #5 05-17-2004, 04:50 PM

These may help:

http://www.landiss.com/mixture.htm

260e mixture adj (calif. car)

http://www.peachparts.com/Wikka/EngineControls

EricSilver · #6 05-17-2004, 05:54 PM

The injector seals (little plastic donuts, basically) surround the six fuel injectors at the top of the engine, visible after you unbolt the air cleaner. The seals cost about $6.00 or so for a set of 6.

The "proper" thing to do is unscrew the fuel lines between each injector and the fuel distributor, and then remove the injector by unbolting it from its seat. However, I only removed the fuel line at the distributor, and lifted out the injector with the fuel line still attached.

Once out, the old, brittle, seal can be (carefully) snipped away with strong, sharp scissors (or broken apart with a nut cracker). Slide the the new seal around the injector, re-bolt it to the engine, and screw the fuel line back into the fuel distributor. Don't remove all the injectors at once, unless you have a photographic memory. Some lines go over or other others, and it is very easy to forget the sequences.

It is a quick and easy process IF, and only if, you have a wrench that can be infinitely angled. If I remember correctly, injectors 3, 4, and 5 were the real b**ches to remove and replace because it was so difficult to uncrew them -- or replace them after they were out -- due to the restricted working space in that area.

If your seals were indeed leaking, you will notice it takes a second or two (or three or four) longer to start after you have replaced them. Although you are technically running lean when the injectors were leaking, you really were not because the car's computer was compensating for the excess air leaking in by pumping more fuel. Now, with the excess air cut off, you will truly be running lean (as I presently am) and the car sometimes needs noticeably more time to start -- especially when it is very hot.

From the photo, I can't clearly see what is leaking. Someone else will surely chime in here, but it appears to be a front seal leak which, I also believe, is not too difficult to repair.