I have a 84 500SEL, What would cause the frequency to increase when the adjustment is rotated clockwise (rich), and and go lean whenI turn it countreclockwise? When I turn it lean untill the engine almost stalls the frequency is 60.2% and stops fluctuating.
When adjusted rich to the point of stalling the frequency will go up to 90%. I am using pin 3 and 2 on the diagnostics connection.
3 is + 2 is ground. If I adjust it to 62-70 the eng. has a significant intermittnet miss. new O2 sensor, cap, rotor, plugs,wires, and fuel distributor. The engine runs like a bat out of Hell on the road. fuel milage is 12 mpg with this miss.
Help!
Mack

Nothing wrong with the mixture setting. It's working as it should. Your miss is either bad injectors, an ignition problem, or a valve problem, it's not the fuel delivery unless you have a bad fuel pump or relay, causing fuel starvation when it stops running or slows down. If it is really intermittant, its very unlikely to be the fuel distributor of the injectors.

Set the mixture to 50% duty cycle and find out why you have a miss, then reset (the miss will cause the lambda control to run it rich).

dirty, clogged, or dripping injectors will cause you to have different mixture in the affected cylinders, so you will get rough running.

Bad plug cables, rotor, cap, or spark box/coil will also cause rough running and mixture fluctuations.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks for your responce;
I cant get 50%, and it is working backwards, if I understand everything I've read on the subject. When I richen the mixture lambda should decrease but it will go to 90.% and when I lean it the system drops to 60.2% , no fluctuation. If I continue to lean it out the engine will stall and the frequency never moves from 60.2%. This makes no sence to me. I ordered injectors, holders. and seals and will be installing them soon, the weather's been a ***** here in Maryland. My question is do you know why Lambda is operating backwards?

It would seem the readings you are getting are codes - I don't know what they mean, other than you are out of loop control. A constant reading is not actually a duty cycle indication.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7

Yes, fixed readings here would indicate fault codes.

A variable reading would indicate closed-loop operation.

Have you checked to see what the current is doing at the EHA?

__________________
2012 E350
2006 Callaway SC560

Bad O2 sensor will do this as well, I believe -- it doesn't respond to oxygen properly. Make sure it's connected and that the heater works (the other two wires to the sensor are the heater) -- it's only sensitive to oxygen when it's about 600F.

Otherwise, this system really doesn't set codes, it just fails to work properly, or quits altogether. Should sit at 50% with a bad or disconnected O2 sensor no matter what you do with the mixture.

Do a search and take a look at the discussion in the DIY section on engine controls -- I think something like this has come up before, but don't remember the thread.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

hey gang, this is an 84-no eha, no codes. go with psfred. good luck, chuck.

Peter has the key. Disconnect the O2 sensor, calibrate your meter. It should read 50%. If it doesn't decide whether your meter is right or your system is wrong.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Thank you all for your help;
No this year MB doesn't have EHA or the ability to give fault codes, nor does it have a heated O2 sensor. The sensor when heated is reading .8 v It's got about 3,000 mi. on it. I jump the connectors to the enrichment switch (which puts lambda in open loop during exceleration) when performing all mixture adjustments. One thing I noted yesterday is if I leave the fuel vacuum vent capped off (the one that pulls fuel vapor when the throttle is open) it almost has no miss. So I'm starting to think a vacuum leak in this vent system? But that doesn't explaine why Lambda is working backwords, and wont go below 60.2% I'm using the craftsman digital meter with the Frequency setting I dont beleave it has a calibration adj.
Thanks again for all your help. This sight has given me an immeasurable amount of help over the past couple of years.

You need to calibrate your meter to the 50% duty cycle that comes with the O2 sensor disconnected.

If you aren't reading 50% then your tool is set-up wrong (or defective). Or you have a lambda system problem.

You need a baseline when doing testing. It is my guess you are reading wrong and that is why things don't work right.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Swap the leads and try that, too -- meter will read inverted sometimes with the leads swapped.

If you don't have an EHA, you have a frequency valve, so make sure that's working, too.

A big leak in the evaporative control system will make you run way lean off idle -- I've had this happen before on our old Ford Fairmont, took forever to figure it out, since the main suction line is closed at idle both by the PCV valve and the purge control line. You can suck an amazing amount of air down a 1/4" line.....

Once I plugged all the leaks, I could suddenly set the idle mixture properly and it stopped knocking on the highway.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!