Air Fuel mixture question - PeachParts Mercedes-Benz Forum

GregoryV022 · #1 09-17-2009, 12:39 AM

how do i know if my car is running rich or lean and how do i adjust the mixture if i need to.

the car im concerned with is my cosworth 190

mbdoc · #2 09-17-2009, 08:09 AM

By using a DDM that can measure duty cycle at diagnostic connector.

Should have 50% on/off ratio measures between pin #3 & ground.

Bill Adkins · #3 09-17-2009, 08:48 AM

You are describing a 16 valve 2.3. Not a simple car by design. The adjustment procedure is correct but there are a number of issues involving intake leaks and linkage adjustment and lubrication not to mention the correct valve adjustment. Get the manual concerning this engine, I think it's available via MB on a CD.
Bill

dhjenkins · #4 09-17-2009, 09:43 AM

I'm old school. If it's gas, look at a plug or two. If they're white, it's lean, if they're brown it's rich. You can google search images for how to read plugs.

If it's lean, look for vac leaks.

Bill Adkins · #5 09-17-2009, 09:55 AM

Newer engine fuel management systems make the color evaluation to a degree inaccurate. Actually a full load run on a chassis dyno with shutting the engine off while coasting down from speed will give a good indicator but casual driving won't reveal as accurate indication.
Bill

dhjenkins · #6 09-17-2009, 10:26 AM

Quote:

Originally Posted by Bill Adkins

Newer engine fuel management systems make the color evaluation to a degree inaccurate. Actually a full load run on a chassis dyno with shutting the engine off while coasting down from speed will give a good indicator but casual driving won't reveal as accurate indication.
Bill

That's true, but only if the vehicle is operating within acceptable LTFT limits. Once engine management has maxed out it's long term fuel trim one way or another, looking at the plugs will still be a valid indicator, especially if it's an extreme condition.

GregoryV022 · #7 09-17-2009, 10:29 AM

i read somewhere that you can tell by how the exhaust smells. but that seemed unlikely.

what factors could contribute to a incorrect mixture specifically.

dhjenkins · #8 09-17-2009, 10:46 AM

Quote:

Originally Posted by GregoryV022

i read somewhere that you can tell by how the exhaust smells. but that seemed unlikely.

what factors could contribute to a incorrect mixture specifically.

Vacuum leaks, bad airflow readings, bad O2/lambda readings, plugged exhaust, restricted intake, low fuel pressure, plugged or leaky injector, bad fuel management or ECM, etc... etc...

It's a long list.

GregoryV022 · #9 09-17-2009, 09:24 PM

Quote:

Originally Posted by dhjenkins

Vacuum leaks, bad airflow readings, bad O2/lambda readings, plugged exhaust, restricted intake, low fuel pressure, plugged or leaky injector, bad fuel management or ECM, etc... etc...

It's a long list.

what would be the most common ones to check first.

dhjenkins · #10 09-18-2009, 10:18 AM

Quote:

Originally Posted by GregoryV022

what would be the most common ones to check first.

Depends on if you're lean or rich...

At your vehicle's age, I'd check for vacuum leaks first (which would cause a lean condition). Take some carb cleaner and spray it around the engine while it's running. If you get a change in RPM, you've got a leak.

You could also get a cheap vacuum gauge (and google how to read it) to check for leaks, plugged exhaust, intake restriction, etc... Shouldn't be more than about $20-$30 at sears. Get a decent one, not an autozone one.

Also check your plugs if for no other reason that to see what the electrodes look like. Fuel management in the 80's wasn't that advanced, so you still have a chance at reading the plugs.

Bill Adkins · #11 09-18-2009, 10:35 AM

Using the carb cleaner around a running engine can have two unpleasant results. First it can migrate in around the air cleaner seals and give a false result causing non required repairs so I made a long snorkle to set on top of the intake housing moving the fresh air source high above the engine. I actually started using a water spray bottle with an electronic stethyscope to listen for the suction noise made when the water hits the leaking intake. It's quite accurate. The second item is the creation of phosgene gas, that happens when burning most spray cleaners into open flame. Dont remember which component in the aerosol causes it but it is really deadly so please be in a well vented area if using this procedure. If you get even a tinge of sting in your nose leave the area quickly.
Bill

GregoryV022 · #12 09-18-2009, 10:59 AM

well a buddy of mine told me to try this trick.

i took a bottle of water and poured it over each injector while the car was running. when i poured it over the number 3 and 4 injector, the car spluttered and coughed. so i guess that means the injector rings are bad. ill change those asap.

could that also be the cause of my weird idling

dhjenkins · #13 09-18-2009, 11:47 AM

Quote:

Originally Posted by GregoryV022

well a buddy of mine told me to try this trick.

i took a bottle of water and poured it over each injector while the car was running. when i poured it over the number 3 and 4 injector, the car spluttered and coughed. so i guess that means the injector rings are bad. ill change those asap.

could that also be the cause of my weird idling

Yup.