Following the excellent advice in this forum, I rigged up a harness to check the EHA current to check if my mixture settings were correct.

KOEO was +20ma and at idle +3ma, fluctuating slightly when I revved the engine.

These figures are OK, if I understand the information correctly, but I could not move the needle off +3ma when adjusting mixture either way, even taking it to the point where it was too rich or too lean to restart the engine.

Tried the X11 sockets 2 and 3 and had a steady, slightly fluctuating reading of around 2.9v, which with a battery voltage of 13.2v equates to a duty cycle of 77% on my calculator. Again, despite adjusting the mixture both ways, could not get any change in voltage. The figure I was after was 4v, or 70%

I resorted to the squirt of carb cleaner method to adjust mixture and the engine's running fine but would like to check this scientifically. Am I doing something wrong?

Car is a 1987 300e, no cat, no lambda and if there's an oxygen sensor I can't find it. Maybe its a pre diagnostic model but if so, must be a way of checking the mixture surely.

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1987 300e manual 250,000 km (sold)

Great idea, and you are doing it right, but you are in the wrong place working on the wrong car.

You have read and are doing well monitoring the lambda control system for adjusting mixture. If there is no lambda system it is real hard to monitor it.

There will be no electronic means to adjust mixture on non feedback systems.

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

Just out of curiosity, why would a car without diagnostics even have an X11 socket?

The first x11 type diagnostic sockets started in around 1973 with 450SELs. The socket was there but MBUSA never had a tool for it. It would have helped with the standard measurements of the day: timing and rpms.

I forget what is in all the pins besides feedback control, seems like engine speed is there. In any case MB put a dagnostic connector up there for years before it even had a tool to connect to it. Hard to say what were their intentions.

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

Kinda like the I.D chip inserted in my Rat Terrier's neck. It contains all his vital info but less than 1% of vets have the scanner to read it. Darn dog will be dead before it's mainstream!!:p

ah, well that explains a lot. Thanks Steve for your input on this, I was following your instructions after all.

Does this mean the only way to verify the mixture would be by checking the exhaust emissions?

The other question that springs to mind is: if there's an electronic adjustment system in place, which I presume is what the EHA is there for, then where does it get feedback from?

I have observed that the car doesn't want to start with the EHA disconnected, which I believe is not the case with later models, so it looks like it is doing something.

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1987 300e manual 250,000 km (sold)

I'm reading these threads,and I'm lost.What is the EHA,where is it,and how do I check in plane english please>THanks for any help.
PS:In french will do to lol

The EHA is on the right (viewing from driver's side fender) side of the airflow meter, underneath the airfilter that needs removed.

Plug your mulitemeter into the disgnostic socket (round,black, ~1.5 inches in diameter-screw off cap).

Set multimeter to duty cycle freq.

Red lead into hole3, black into hole 2-that is your ground.

Key on engine off (last position before starter engages) you should read a number.

Start car, you should read another number.

After the car warms up, and if you HAVE an O2 sensor, the numbers should change, and begin to fluctuate.

You do NOT need to touch the EHA for the procedure described above.

However, EHA current (which is also a representation of mixture) can be measured, and this is most easily accomplished with the MB EHA test harness. If you simply want to check mixture, either method will suffice, and the data supplied is equally useful.

PS- you didn't mention what MODEL and year your car is. Sure hope its a KE3 car, or this is going in the wrong direction!

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

To clear this thread up.....


On a car with no lambda, the reading on the X11 port is used for diagnostics just as on lambda cars. But no lambda reading is ever output - it should just read 50% if there are no diagnostic errors meaning 'no errors'. But the mixture might still be miles off of course. So if your car is not-lambda and you got 77%, that probably is actually 80% which can be compared with the images on this page for what 80% means:

http://z14.invisionfree.com/mercedes_190_club/index.php?showtopic=6104

to see what the self-diagnosed fault is.

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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg

Well, it was two and a half years ago and all that worry about incorrect mixtures turned out to be symptoms of a much larger problem. Spent a lot of time learning about the fuel system though.

Self-diagnosed fault turned out to be water in the petrol tank...

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1987 300e manual 250,000 km (sold)

Received my EHA test harness from the MB Dealer today, UPS
Total cost $32
Part number 102 589 04 63 00

Will test out the EHA voltage this week. ANy guides on how to use it? Two of the connectors will go on the EHA and only one will connect to the EHA wire harness. So far I was getting some weird and High voltage readings. I was expecting the reading to be around zero and I was getting closer to 12 volts.

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red

On non-feedback models, the mixture must be set with a CO meter in the exhaust as there is no O2 sensor providing that information. The fuel computer will use the EHA as an enrichment device for starting and for throttle opening via the resistor wiper on the air flow meter, plus usually shuts the fuel off on closed throttle deceleration. It will read 3 mA all the time except with ignition off, closed throttle coast, and during throttle opening events.

Peter

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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!