I'm going to have to hope an experienced tech will answer this one for you, as I have never seen the inside of an MB cat, although at the point where you see a drop in fuel economy and performance, any damage to the cat internally, if it is to blame, should be obvious.

Connect the VOM to the O2 sensor output - pull the connector apart just enough to get the probe in without disconnecting O2 sensor from the circuit. A VOM should measure about 450 mV. If you can test the O2 sensor with a scope, it will show the wave form and the output should jump back and forth between about about 0.2 and 0.8 volts a couple of times per second. This is the best test for O2 sensor health. Also test the O2 sensor heater, which is the two wire connector. Check for system voltage on the harness end, and continuity on the 02 sensor pigtail.

Your high CO readings indicate a rich mixture, so the Lamda system is probabably not functioning properly. A common culprit is a faulty O2 sensor. The Lamda engine temperature sensor could also be fauly - sending a false low temperature signal, so the system always thinks the engine is cold, or it could be the EHA or control unit problems.

Duke

Got 14.xV from heater connection (Brown=ground)
I got a reading (by puncturing sensor side of black wire to ground) of 0.451V at start up (coolant temp 80°C) slowly (over 20-25min) descending to 0.349V.
Increase of rpm to 2500 would raise reading to about 0.360V at bottom end of the reading.
That and this...
are leading me to coolant Temp sensor...

Coolant temp sensor reads 475Ώ at 95°C (aprox.) out by more than 100.
Normal range is 290-370 Ώ at 80°C should be around 220 at 95°C
Is this a typical sort of failure?

Edit: retest - am getting 720-750 Ώ at 80°C (reversing-polarity for cross testing) and dropping but, is not in correct range

Can I jumper this to 0 resistance to see if it runs good or is that not ok for computer?

What do you mean by "reversing polarity for cross testing" Are you saying that when you reverse the probes you get a different resistance reading? The thermistor should read the same regardless of which probe is on which connection.

If you believe that the sensor is bad then you could hook up a resistor of what ever value it is supposed to be at running temp and if the engine is at running temp then it should be happy. I don't think zero ohms would be a good idea.

Sorry about using confusing/wrong term. the readings are consistant as I reverse the probes (close enough) as they are moving lower at 80°C. They never make it to correct operating range though.
Good idea. I will have to go get one.
Thanks for your response.
Marty

Unplug the O2 sensor and look at its open circuit voltage. It should be over 450mV. Engine and exhaust must be fully warmed up. Also check for continuity of the O2 heater.

I have the following temp sensor values for '84 M102. I'm not sure if they apply to later KE systems, but I think they do.

20C 2.2-2.8 Kohm
80C 290-370 ohm
100C 140-220 ohm.

Take readings at two temps - 20 and 80 are probably easiest.

Duke

am pretty sure it is rich.
I had a center muffler failier around Halloween, when I replaced It (both it and rear muffler had been off for 1½ months) I expected to see a big improvement in mpg that never appeared. It has been a little slugish as well.

Was that temp sensor on your 86'? If so where is it exactly (side of the block?) and any tips on the test?


I think all the temp sensors are suppose to be 2.6-2.8 k ohm. Sounds like you could really use a factory manual=)
AKA looks like my dash gauge might also be shy by about 5 C. At 100C, the sensor read about 800-900 ohms. I was thinking the range should be 500-600 ohms-but don't know without checking a bosch book.

I'm headed for emission testing soon too. My plan of attack is new plugs, oil change, and O2 sensor. It did not start today instantly at 75 F, so I'm guessing my mixture is off a bit.

Michael

Though it may not seem so I do have the manual. The emissions world has been to me like aincent greek but I have learned a lot in the last 72 hours.

I found the water temp sensor Ohm's range at the temp chart in the /Engine Manual-Combustion Manual-07.3 Mechanical/electronic gasoline injection system (KE injection)-121 Testing electrical components of KE injection system. page 60

Temperature °C........Resistance kΩ
-20........................15.7
-10.........................9.2
0............................5.9
10...........................3.7
20...........................2.5
30...........................1.7
40...........................1.18
50...........................0.84
60...........................0.60
70...........................0.435
80...........................0.325
90...........................0.247
Same resistance values apply to KE intake air temp sensor.
I think this chart applies to these 2 sensors for all KE systems but don't know for sure.

My water temp sensor is not in line with these values.
I may also have a bad o2 sensor (wish I had a scope to get a clear view)
Now I am waiting for my water temp sensor to arrive.

75°F ay...must be nice.

Marty

P.S. anyone know if there is a better tool than a 22mm crows foot to get these sensors off and on again?

I see it is a deep 22mm socket (on water temp sensor).
I will post my results when I have them.

Marty

Good luck....

Been there last Saturday. Unless you've got a fancy Stallwillie or they revised the lift bracket.... revise your game plan.

You'll need to take the 2 6mm allen bolts out and rotate the bracket out of the way. The bracket has the water oulet for the head.. so if you do it carefully- it won't leak. If not, drain the coolant and replace the o-ring seal while you are at it.

Looking at mine- the coolant gauge sensor is out of range by a similar amount. The fan switch- I cannot remember it comming on even parking the car in 100F weather. So, I'm guessing that isn't right and it needs replacing too.

There are seals underneath the sensors...

Makes me wonder about the sensor on the intake too...

Michael

Whats a Stallwillie? Sounds like what I've been looking for

I did that fan switch last spring. Its really wide on top so no socket can get over it. I really butchered the thing getting it out and if it had needed any torque, I would have been in big trouble.

Good point. The scary part is if it the water temp sender (engine temp on gage) is off by much it would really be screwing up my calculations on the water temp sensor.
Thanks for your input Michael I should be able to put my water temp sensor in in the morning in this snow we are having, and I'll post my results.

Marty

Try www.stahlwille.com. Exchange rate sucks these days... but their wrenchs, sockets and definately the allen & torx sockets are better than snap-ons. Infact, I've thought about liquidating some of my mac and snap-on stuff on ebay and trading up to stahlwille.
The only on I see might be one of the MB a/c crowsfeet. 440-22?
Not that hard to do... I'll let you know about the temp switch in a week or so.

Michael

http://www.samstagsales.com/mercedes/mb000589710300.jpg

I'm guessing this would work or you could make something similar.
Kinda rich for my blood though... could use it on A/C and torquing those front struts=)

Michael

Well its been a while but I have finally got her running and am ready to have emissions retested. The first appointment I could get is for Tuesday at 10AM

So far I have:
Changed the water temp sensor.
New cap & rotor.
Oil change.
2 big bottles of Techron in a tank of 93 octane.

Being a nervous type I was looking at my duty cycle at X11 (engine fully warmed). It starts out at about 45% and fluctuates but it heads down to the just under 10% range and fluctuates around there (8-12%). Is this ok? I was thinking that it should fluctuate closer to 50% but don't really know.

I just want to do whatever I can in the next bit of time before the test to improve my chances. I have read Duke's instructions for fully warming up these cars and keeping them at high idle right up to the test. But is this duty cycle reading an indication that there is still a problem with the lambda system?