Hi Steve:

I tracked the wire from the O2 sensor and it goes to the big computer style connector (its taped into it with electrical tape so they spliced it in there I suppose) that plugs into what I presume is the computer of the car behind the battery on the wall. Its a big rectangular black box with the printer cable style connector plugged in the top of it.

In front of the battery, on the back of the firewall, I only have one connector which goes to the brake pad sensor to light when the pads are gone. So, no diagnostic connector at the passenger side.

I guess I really have one of the first versions of the 190e and it seems to be alot simpler than the others here. I have that screw to adjust the idle speed, the mixture adjustment screw, the added O2 sensor spliced into the computer, and no pin 3 connector in the X11 hole #3.

What would be the best course of action now? That O2 sensor was installed in 1986 by the way so could it still work or is it faulty by now? Its only seen about 90k miles since it was installed (I have 120k miles on the car) but many years of living in that exhaust pipe...

Thanks for your help, as always, it is much appreciated!

-=>Raja.

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1983 MB 190E, bought from Germany and shipped to the US in 1986.

I presume the car has KE with an EHA. As with all KE cars the easiest image of what is happening is to monitor EHA current.

One can see all the forms of electronic correction at work cause that is how they work: by changing the EHA current. The early KE cars were all positive current and lambda had correction in the range 0-16ma. The car was adjusted to 8ma in closed loop. Monitoring EHA will tell you if you have closed loop.

If you can open the circuit to the O2 sensor the range of lambda correction can be determined by the "through the Captain" method (search the archives).

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

Hey Steve:

Here is another post that I wrote when I checked the figures from my EHA:

"Hey guys:

I've read around on the posts here and learned a few things thanks to all, but I am a little bewildered on how to set my mixture right on my car.

From what I read, people say I have to put an amp meter between the EHA and it should read 7 to 8ma current draw at idle if the mixture is set right. Someone also said I could check this also from pin #3 on the diagnostics port. Well, I went under the hood this evening and here is what I found:

a) I don't have a pin #3, its missing in the hole. #1 has about 8 volts or so, #2 0.0, #4 is 13.7, #5 is 13.6, #6 is 12.6 and #7 through #9 are 0 volts to ground when engine is running at idle.

I put the amp meter between the EHA, and it shows -0.14ma when engine is at idle. If I step on the gas, it jumps up to 4, 5, or even 7ma, but then quickly returns to -0.14 or so.

I found out that you have to push down in the aircleaner hole with a 2.5mm wrench and just before the engine dies it engauges and you can rotate the mixture setting. Makes the engine run slow and rough or smooth and fast. I played with it a bit but the amps remain at -0.14 at idle. I did readjust idle speed with adjustment screw when I played with mixture settings, but no luck with getting EHA voltage to 8ma. What gives and where do I go from here?

I want to get the mixture set right as my car is hard to start hot and I want to eliminate this as an issue. Dialing it in by ear seems to work, but I'd rather do it scientifically with a voltmeter if someone will be kind enough to tell me how to!

Thanks!

-=>Raja."

I will go search for "through the Captain" as you suggest to see what those words might mean. I drove the car today to work and it seems to hesitate slightly with part throttle (it feels like its missing or something) and I think now that I read some of the DIY information its hesitating around the 2k to 2500 rpms range. If I am on the highway I don't feel any hesitations - they only appear from 40mph to 60mph or so. If I throttle the engine up by hand while I'm under the hood, I can feel the engine "pulse" a little bit as its running say 2k rpms (no tach while I am under the hood). Idle is smooth, fast idle is smooth, 3000 rpms and beyond is smooth, just the midrange is not good. I'm thinking maybe its the mixture screw to fix that hesitation at part throttle?

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1983 MB 190E, bought from Germany and shipped to the US in 1986.

Mind my ignorance, but what is closed loop mean?

Dumbo mechanic but at least with the desire to become knowlegable about cars!

-=>Raja.

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1983 MB 190E, bought from Germany and shipped to the US in 1986.

There are a lot of terms that I trow out and most have extensive discussion in those phrases in the archives. I have writen detailed descriptions of "closed loop" and "EHA monitoring criteria" on these forums more than once; and so have others.

The term closed loop is not just an automotive term. It refers to a method of control. Basically it means that in order to do overall control one designs a system to do a function with measurable output. One then monitors the output and changes the input to keep output exactly within bounds. In an auto engine management system the O2 sensor is used to do the measurement of output (exhaust oxygen content to be exact).

From your EHA readings it sounds like there is no feedback control (another variation of the closed loop concept). That is the purpose of the "through the Captain" test. It will give you your controllers capabilities.

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

I think I will finally go for it: However, I have some doubts after reading the "Bosch KE3-Jetronic Mixture Adjustment" document:

Do all of the cars have the tamperproof tower/ball? If I remover the filter cover, can I check that?

When testing the duty-cycle measurement before turning on the engine, it says that you must deflect the air flow sensor plate to test the idle contact: does that mean that I should remove the filter cover and press the plate down a few mm or what?

Thanks for your help.

I have done some measurements at pin-3 of X11 connector, as commented in other post, although repeated here for reference:

When idling, I see about 50% duty cycle, fixed there until the car warms up or, if hot, for several seconds. Then it starts fluctuating around 40-45% or so.
If I accelerate , the average duty cycle decreases to about 25% at 2000-3000 rpm, fluctuating +/-5% approx.

What does this mean? Shouldn't both readings be very similar and around 45-50%?
My car doesn't have an idle mixture adjustment, so how can I correct this, if something is not correct?

Please share your experience. Thanks in advance,

Sergio
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1992 MB 190E 2.3 (8 valves)
1995 Renault Clio 1.9D
1993 Citroen Xantia 1.8i (sold)
1980 Renault 12-TS (gave away)

Yes, the duty-cycle represents the correction necessary to achieve the mixture required. When it is different it means the effective mixture is different.

In your case the mixture is richer at higher speed. That actually translates (usually) to the mixture being leaner at idle. This is the most common way it will be off and usually represents small airleaks or injector flows that are poor at small flow rates. One must remember that the mixture required is barely that which is necessary for good running.

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

Thanks.
Can this affect performance or only idling?
How should you correct this, altering the mixture setting?
Thanks!