My LAST ovp/eha question, I promise!!!!
 

Here's the deal. Couple of years ago I replaced the old style OVP hoping to correct stalling. Didn't help. Well, a while back the car would not start at all. I still had the old OVP so I plugged it back in. Car started but the old stalling problem that never went away is still there. Check engine light on/off/on/off and eventually engine dies.
Fast forward to today. Gas mileage is poor so I'm gonna take one more try at reading Lambda. I also have my DMM in series with the EHA. Now, I have my analog meter in pin #3 of the X11 connector. Key on ignition off EHA reading 19.95 ma. Start car. Analog meter at pin#3 reading at 12 volts. EHA ma bouncing all over the place!! Adjust the mixture screw and eventually get the Lambda on 7 volts. Old M103 is purring like a kitten but raw gas is dripping out of the tailpipe!! EHA current has never "settled" on any value. Then suddenly the Lambda voltage drops to zero and the car dies. What the heck am I seeing?? Did the OVP have anything to do with that?? Or did the EHA have a hand in it?

Assume that you've checked or replaced your O2 sensor and checked the connection?

O2 sensor was replaced and is working.

You must resolve the eHA current issue. 20ma is appropriate for key on, ENGINE off readings. The next step is to disconnect the O2 sensor. The ma reading should be zero with the engine running!!. If it is different this issue must be resolved.

If you have 0.0ma then try grounding the computer side of the O2 connection. This should cause the ma to slowly correct to the maximum which is about 12ma. Next place one hand on twelve volts and hold the computer side of the O2 connection with the other hand. (this applies a small >1v signal to the controller) You should slowly go to -12ma, full correction lean.

If the system has the ability to do this, the next step isn't so easy. The next step for testing would be to watch the differential pressure and to verify that it is .4bar and that it moves .1bar greater at 12ma and goes .1 bar less at -12ma.

Control is then working. See what you get with the O2 disconnected.

Her's what happened,
Ignition on, engine off = 20ma
Disconnect O2 = 0.00 ma eventually (10 seconds)
12 volts thru Cap'n = 9.9ma (engine 'coughed' and went to zero then slowly climbed back to 9.9ma)
Controller O2 wire to ground = 13.8ma

So it looks like electronic control works. You should have gotten negative current flow in the 9.9ma direction.

This range of control will usually make the engine run poorly in one direction or the other. Remember that when you ground the O2 input the system thinks the engine is lean and it richens up the mix by the 13ma (in your case).

The next step is to set the basic (uncorrected) mixture to .5 to 1.0% CO. This is hard to do on MBs because there is no precat test port.

Since the system seems to respond to created O2 signals, one might suspect the real signal, but lets test it. Hook your volt meter to the O2 sensor lead (leave it disconnected from the controller). If you get 1v the system is rich (or the sensor is lieing). Use the 12v thru Cap'n method to lean it out. Does the method make the engine run poorer? Does the voltage drop below 1v?

Lost me here. How can it make the engine run poorer if it's disconnected? I am testing a disconnected o2 sensor on the sensor side for both tests, right? Would the engine even need to be running for this test?

This is a great way to test the controls, I'm dying to try it on my 190E already.

Thanx for the great posts.

xp

In the last test I mentioned, the concept is to run the car and evaluate the mixture by seeing how it affects the O2 sensor voltage. The sensor is a 0 to 1v voltage generator. It creats voltage that is related to engine mixture within a small range.

Its very likely that the sensor is fouled, but the way to tell is to run the motor (the sensor has to get hot which requires time and engine speed - don't be in a hurry), while monitoring the voltage (sensor on its own not connected). As I stated its likely to be either 1v or zero volts. If its one volt and its working then the mixture is greater than 1% CO (if measured before cat with an exhaust gas analyser - which you really can't do anyway). Here is why I suggested to do the 12v thru Cap'n mixture change. This will lean the car out and unless your are very rich it will bring the mixture through the range 0-0v - 1.0v. if not you can lean it out till it does.

Remember a proper working O2 sensor measures mixture from 0% CO to 1% CO. This is a very small range. The car will start running poorly above 6% CO and below 0.2% CO (maybe higher). The car will be held to mixtures in the range of .3% CO to .7% CO by a functioning system and it can only correct a rich car running less than 4% CO.

If everything is functioning you will be able to lean out the mixture till the O2 sensor just drops from around 1v. Then you will be able to reconnect the wire and the system will correct mixtures less than .5v by adding fuel (within the 10ma correction range we have already tested) till the mixture becomes richer than .5v at which time the current will reverse and the system lean out till it switches the other way. Once the O2 sensor is hot and everything is adjusted then the .3v to .7v O2 sensor swings will be kept in check by about a 4ma total mixture correction.

If this were a training course this would really be a short story. If you don't understand ask me again.

I re read your post about the O2 sensor test and understood it that time. I re did the EHA test and got the same results. ( and it was -9.9 through the Cap'n. My mistake) I left that hookup and used my handheld DDM for the sensor test. 0.00 volts any way I tested. Even through the Cap'n 12v test. So, sensor is fouled right? Doesn't surprize me, there is more soot under the tailpipe tip than in my fireplace!! But there are two more oddities. Engine is surging wildly and shutting of regularly while warming and would not restart without depressing the accelerator. Also, there is no voltage to the O2 heater connector.

Instead of starting another thread I'll just tack this here
 

Can the O2 sensor be cleaned? Also, are these tests gonna work if I have a leaking fuel distributor?

Yes. The best way to clean it is to get the engine running properly and then run it slightly lean. Run the poop out of it. Then either test it again or hook it up and verify closed loop control probably after some driving and resetting of mixture.

You eventually must understand closed loop control to understand the system and the various ways to adjust it electronically. Closed loop refers to the fact that the mixture is kept to a precise range by feedback control. The system is made to go rich when it senses lean; it doesn't go far till it has effected it enough that it is now sensed rich and the control heads lean. This back and forth control keeps the average mixture to a very tight band at the exact relative amounts of fuel and air for complete combustion.

If you can get the closed loop to react doing a couple of cycles a second at 2000rpms you have cleaned the sensor.

I have taken the Lambda adjustment screw to full operable lean when hot and it still drips raw fuel from the tail pipe. I have taken it so far lean that it won't even start cold! Again, my question is, If the O ring in the fuel distributor is leaking, are any of these test valid??

The o-ring at the base of the fuel distributer seals vacuum.

Where do you have a fuel leak? Is it at the EHA? I would always advise fixing fuel leaks first. If the leak is at the EHA I don't think it would keep you from doing these tests. If its at the EHA I would worry that the EHA wasn't doing its job, But I wouldn't worry long because fuel pressures tell the whole story.

Mixture correction at the tower is usually done within a few degrees of rotation. basic calibration after a fuel distributor exchange might require a full turn or two. I have turned that screw many, many turns and have never reached an END. How much are you turning the screw to go from poor running rich through good running to poor running lean?? Does this even happen?? Forget about cold till we get warm right!! First warm, then closed loop and then maybe cold.

There is a puddle of fuel in the manifold under the throttle body, visible when the airflow plate is pushed down and the throttle is opened. The lower housing of the fuel distributor is damp also.
On the adjustment issue, the engine will run only in a very limited range of adjustment, with the screw approx. 30 degrees either lean or rich. When adjusted hot toward the lean side it runs well, but will not start cold in that setting.

I could use some help with the EHA too
 

I have a problem with the EHA and the current going through it. the car is a 1985 190E 2.3 so the current in only positive.

I always thought that the current should go higher when taking off from a stop to richen the mixture and then go down a bit as the car gains speed with even acceleration.

My car does the opposite. When I step on the gas with a MM hooked up to the EHA, the current jumps up to 2ma and then drops to 0, this is when warm already. It will start going up slowly once the engine goes over 2k rpm, but before that 2k it hesitates and pops due to running lean from what I have found out. This is not always the case but 95% of the time, and it pops a few times a week under hard acceleration. Another thing I noticed, when cruising above 60kmph, when I left go off the gas, the EHA current jumps up to 56ma, which I thought was only supposed to happen on start up.

I'm trying to figure this out to get rid of my hesitation and this is where I found the problem, but I'm not sure what is causing this current to be so sparatic.

I have new copper spark plugs, distributor cap and rotor arm coming in in the next few days, new spark plug wires are already on, but for some reason I don't think this will help me at all.

I think I'll go pull out my OVP and see if it works at all. Maybe that's the culprit.

Any help would be greatly appreciated.

xp

I'm going to beat you guys till you understand this.

If you start at zero or wind up at zero with the early 190 system then the system is pegged. For the only positive current systems the nominal adjustment would have you at 8ma. Again pull the O2 sensor and you will see the middle of the road position for either system. The 190 will go to 8ma and if you ground the sensor input to the controller the system will correct to its capability 16ma. if you do the voltage through the body bit you will have it removing enrichment and it will bottom at zero ma.

What you have to remember is that in a perfect system the needed correction at idle would be the same as at 2000 and at 4000 rpm. The correction due to feedback (O2 sensor is in the exhaust and its is after the fact - feedback) should only affect discrepancies to ideal. Other aspects of the system will change mixture. When you step on the gas, instantly the airflap drops. The speed and ammount is proportional to how fast and how much gas one gave it. The airflow potentiometer gives this reading to the controller and increases the momentary mixture correction (adds fuel correction) by adding ma. Sooo... at any point if you stomp the gas there will be an increase in current, once the moment is over the correction will go back to steady state correction which is buried in lean correction if at zero ma on a positive current only 190 system. I think this 190 system stopped in 1986, so don't the rest of you get confused. They quickly decided that better control and a much superior limp home was achieved by having plus/minus current correction.

The plus/minus correction allows zero ma to be the center and a well adjusted car that looses electronic control does great in limp home since all steady state mixture would be at exactly where it was supposed to be anyway - zero. The pos only systems are in the middle at 8ma, when electronic control leaves it goes to zero current and this is the maximum lean correction which doesn't make a good limp home condition.

alright, I understand that but...
 

stevebfl just one more thing that does not make sense to me.

if for the pre 86 cars the middle is 8ma, why does my car drop down all the way to 0ma when I'm coming to a stop, and then it refuses to go back to 8ma until it goes over 2k rpms. The car will hesitate and miss because of this, but as soon as the current jumps up, it takes off like a rocket. Would adjusting the Air flow sensor pot correct this? Because it won't matter how much gas I give it from a stop, the current will remian at 0 until 2k rpm is reached.

Tomorrow I'm getting my tune up kit, so I will see how the car does, but the parts that will be replaced have nothing to do with the electronic controls of the engine.

If it does not help, after I do my driveshaft, I will get a new pot for the Air Flow sensor, I believe it to be faulty, but I can still try to adjust it a bit.

Can you suggest anything?

xp

Your car drops all the way to zero because it is not in closed loop. If the system is functioning your car is doing this because you are toooo rich. Zero current is the maximun lean correction possible within the lambda system.

I can explain this but that is not to say that your car will run at the required mixture. Most of my life I dealt with cars that in no way could have been made to run as lean as is required to go closed loop at lambda. If you really wish to understand this, give me a 500 word essay explaining that last sentence; most importantly: going closed loop at lambda! I feel that most do not understand that concept.

I can't say I blame people for not understanding it. The concept came out in 1979 (with Volvos - 1980 for MB). I worked around the system for five years before in 1984 we started bringing in grey market cars and had to design feedback control systems to feed three way cats. We were tested on the results. Nothing like failure and money to breed understanding. I worked in the dark for nearly 5 years on these systems.

now for getting it back into closed loop
 

Thanx for the explanation stevebfl, it seems that you know a lot about this, I've been trying to figure this thing out for quite some time now but I never got any concrete answers, so maybe you can provide some insight to this if it's not too much trouble.

So far you are exactly right, the car does run rich, very rich actually, I pulled the spark plugs and every single one was covered in a LOT of black powdery residue. I also know that the mixture adjustment screw has been tampered with since the cap is gone, and who knows how it was adjusted. I'd like to get the car running with the right mixture.

I think the car can be much more economical then it is right now. I'm no mechanic yet, so I try to take things slow and make sure I got all scenarios covered before I proceed because I simply don't want to mess anything up.

Would you say it would be a good or bad idea to try and lean out the mixture by adjusting it with the screw on top of the fuel distributor since the electronic controls can't lean it out anymore even when the EHA current drops to 0. I know you can verify this with the duty cycle meter hooked up to pin #3 on the diagnostic port, you also mentioned you always richen the mixture a bit for performance reasons, I guess I should follow your lead.

If this adjustment does fix the problem of the engine running rich, will it put the system back into closed loop? I understand that failure of any of the subsystems will throw it out of closed loop.

One last thing, why would the EHA current jump to 56ma when the decel switch is engaged while cruising above 60kmph, once the speed drops below 60kmph, the current drops to 8 and heads down to 0, any idea what could be causing such a big step there?

I would appreciate any help you can give, I hate to be a bother but if you could just point me in the right direction, or a source where I could find out more about this system, I would be forever grateful.

xp

The simple answer is.. yes, lean the mixture out. If everything works as it should you would turn the 3mm adjuster counter clockwise till the EHA current started to rise. You would be doing this slowly and the first sign would be a few ma 2-3 say. In small steps one would then continue til the average EHA current was 8ma (except I like it richer so stop at 6ma).

The problem is it only works this way on a clean system and yours is most likely fouled. To resurrect the system I advise disconnecting the O2 sensor and hook your volt meter to the sensor end. Before adjustments you must be seeing about 1v. It takes this kind of reading to cause the EHA current to go to 0.0ma full lean correction. Now adjust the mixture (CCW -lean). Rev and hold the motor at 2000rpm. Did the O2 sensor voltage change (be sure to hold a constant throttle when reading O2 sensor voltage as the voltage always goes off scale with throttle movement - the scale is 0,0v to 1,0v)? As you hold the car at 2000rpms continue to adjust the mixture lean. You eventually will lower the voltage (or the engine will run badly). If you reach running badly before a voltage change, we have a problem.

This problem will either be a sensor problem (be sure to leave the heater coil connected when reading O2 sensor voltage - even though voltage dropping to the sensor from this circuit is the common problem of such faults) or a separate problem that won't allow the engie or individual cylinders to run that lean. Remeber the amount of fuel we are trying to achieve is the absoilute minimum for efficient running. At such settings any restriction or added air causes fouling. Cause the flame to burn out (if it were a candle).

Anyway, aftyer you get the voltage to start reading, get the number as low as the engine will run sort of good. Rev the motor a few times to 3k or more, hold it at 2k for 10-15 seconds and then reconnect the O2 sensor and see if closed loop can be maintained at around 6-8ma.

Remember closed loop is the distinct cycle of lean rich lean rich correcting. Once this is happening the current will be real sensitive to mixture. Placing ones finger lightly on the airflow meter should be seen on the mixture correction. This will show you how much the system has the ability to correct. If you place a finger on it for say ten seconds and the mixture corrects back toward zero ma what will happen when you let up on your finger???? The system will have corrected lean and will be lean and correction will run way above 8ma for a while til recovered. Watch all this happen and it starts making sense.

God bless you Steve. You must have children......you have the patience of a saint.

I think the contributions you and a few other senior members make keep several of us in Benz cars we would have abandoned/sold long ago.

Thanks again.

Tinker

God bless you Steve indeed.

And a thousand Thank yous.

I think this is the answer I was looking for for the past 9 months.

xp

I'm inventing a new word, "Threadjacking"
 

Now, If I could only find out what's causing my puddle of fuel inside the manifold!

Oh Stephen. You poor soul. You did get thread-jacked.

I hope you get this sorted-out...:)

Well for some things you just have to be there. I have never looked into a manifold that wasn't wet but if you have raw gas accumulating there in any sort of quantity, what we have been talking about is irrelevent.

Clean up the mess and check to see if it returns. Unbolt the fuel distributor and lift it while bypassing the fuel pump relay to maintain system pressure and see if it drips from the plunger. If you have a leak you must address it.

I have already separated the upper and lower halves of the fuel distributor, dried out the manifold, and reassembled. Fuel puddle came right back. Fuel is leaking inside the distributor. There are no external leaks. And for what it's worth, I rechecked the voltage for the 02 sensor heater today with the engine cold and had 11.85 volts while cranking, so I have to assume the heater is working. If I do have a leaking fuel distributor, is it even possible to set Lambda?

Very nicely said Tinker!!

Cap,

The only thing I could think of that would cause a pooling of gas in the manifold is the O ring that seals the plunger in the fuel distributor. DON`T take it apart without measuring the plunger height. It is a critical adjustment. BUT the O ring is available from the dealer.

Just a thought.

Tinker

Steve, does this concur with your thinking? Can a defective EHA cause this sympton? As stated there are no external leaks.

What you describe is to me an external leak. The fuel should pass through the fuel dist and into the injectors without leaving raw fuel anywhere else. If you were to lift the fuel distributor from the airflow meter there should be no fuel dropping from it.

One could test this by removing the dist and leaving the feed and return lines coupled to it. I would plug the injector lines to keep fuel running out the outlets from obscuring the test.

This is what the lower half of the ditributor looked like when I inspected it earlier. It was wet from fuel.

It seems the interest on this one has cooled, so I'll pull the distributor and try to replace the seal myself. (Fools rush in where Angels fear to tread) What have I got to lose?? It's isn't driveable like it is.:(

It's fixed at last
 

Stever, you are my hero

I fixed it just like you said to do. I warmed up the car and had a multimeter hooked up to the EHA current. Sure enough it started dropping to 0 slowly but right away since the computer was correcting the mixture. When I unpluged the 02 Sensor the current right away jumped up to 8ma, plug it back in, it fell to 0.

So I left the 02 sensor pluged in since it was obviously doing it's job and very slowly turned the mixture adjustment screw ccw, gave it some gas held it in place, relesed, and I could see the current slowly rising, but I had to make about half a turn before I started seeing the current go up. Eventually I had it at 8ma where it should be, the engine hummed perfectly, the 02 showed .5-.6 Volts, which is a bit low, so I might have emission problems, and I accidentally killed the engine when I pushed the 3mm allen key in a bit too hard, too much fuel drowned it. When I had it at 8ma right on, the engine would not start, so I had to turn the mixture screw back just a tiny bit. Now it runs like a dream, NO Hesitation, no Missing (so far, I just did this yesterday morning and drove it twice for a few minutes) and hopefully the fuel economy will jump up too.

I will make a seperate post for this just in case someone might find it uself to fix their problem.

I also put the right spark plugs, new distributor cap and rotor arm to finish off the repair, next fill up I'm adding some fuel system cleaner to get rid off all the deposits left after it's been running rich.

Once again, Thanx a million Steve, if I ever get a chance I'd love to thank you in person.

XP

300E Running good yet?
 

Hi Cap'n Carageous and all...

I was just wondering of your 300E was running good yet, because it seems that I am having the exact same problems that you have had or are still having. Fuel build-up below throttle valve, so much that it will not crank, so I have to remove the new spark plugs and dry them, then it will crank and flood again, only to die and do the same process over again.

I have tested many components, and have new parts as well...cap, rotor, plugs, wires, fuel, filter, rebuilt head....let me think some more...lol...

Basically I thought I was getting a good deal on a blown head gasket 300E, but now I'm not so sure why God chose me to save this car from the junkyard (crusher actually :D).....but as we know, God works in very mysterious ways:) ....so I won't complain.

New tires and chrome rims make it a great looking car to come home to, even though I can not drive it out of the yard...even to get the new tires (0 miles) out of the same spot that they have been sitting in for over three weeks! I got Cooper 225/55R16 tires, with aftermarket Benz chrome rims. Maybe I could get the engine running right and sell the engine & trans, then transplant an engine of choice...a 1970 340 Dodge engine (nickname "Baby Hemi)....parts would be very reasonable and I would increase my horsepower under the hood! LOL! I would then rename it to a 340E!! :D :) :cool:

What do you think? Also, I have wanted to conduct a poll to ask viewers if they would be interested in modifying their Mercedes to outfit it with an American made V-8 drivetrain.....what's your thoughts on this? I also want to start a 300E car club, for 86 to 91 (no 4matics)...

Looking forward to your reply and thoughts.

Attachment: My next preference of transportation....non-Mercedes and very unconventional! :D

I am Flabergasted!!!
 

My 300e continues to confound me. Like you I am considering an American drivetrain in mine but haven't had the time to do it yet. I would like to remove the name "Bosch" from my car since the components are unreliable and cost ten times what they're worth. I'm hoping that one day I can install a Ford drivetrain and fuel management system and have a great looking reliable car.
I'm not a MOPAR fan but if you can pull it off, then you have MY admiration!!

PS. As far as saving our cars from the 'crusher', I may be doing my car a disservice!! I think it would make a great toaster!!:D

I know your pain....
 

I know your pain you feel with your 300E...mine is loading up, possibly the seal under the fuel dist. (not o-ring, but leaking seal). On cold start (attempts that is - lets not get happy here thing this thing would crank:D ) it will almost sound like cranking, then simply spins over. When the spark plugs are removed and cleaned & dried, it will crank again, but only if I dry the plugs, and spin the engine over while the plugs are removed. My air flow meter chamber is wet also...too wet...too much fuel, fouling the plugs.

This process is getting old....disconnected O2 sensor did no change...EHA disconnected no change, adjusted air flow meter plate, no change. Like Steve said earlier, it is getting too much fuel. I will be looking into it tommorow, after buying plugs to plug off the injectors and pressure test the fuel dist. for leaks on the underside (with 7 & 8 pins shorted in the fuel pump relay plug).

I just bought a cool domain name pertaining to fixing your Mercedes.....it's http://www.fixmymercedes.com and it will be up & running soon :D....within a few days....maybe I'll post photos and technical data concerning the issues I have had with my 300E! :)

Top of the day to ya! ;)

WOW, I see you revived this old thread. Good info in here.
I tried contacting you before, no response, I am in Clayton, NC.
If you need a helping hand let me know.

I forget which thread it was, but I posted that my car attempted to use all the gas in world! I replaced the fuel pressure regulator, all six injectors and even the ENTIRE fuel distributor/airhorn assembly to no avail. Only after gutting the catalytic convertors did it return to respectable fuel mileage.

Hi Cap'n!

I am currently also confused with my EHA readings and just discovered this interesting threat.

At the point were Steve lost you I am still lost. Steve says: "Hook your volt meter to the O2 sensor lead (leave it disconnected from the controller). If you get 1v the system is rich (or the sensor is lieing). Use the 12v thru Cap'n method to lean it out. Does the method make the engine run poorer? Does the voltage drop below 1v?"

What did you do exactly? I understand that I disconnect the O2 sensor and that I measure the voltage with the engine running. But with the sensor disconnected, how do lean out the mixture? I thought if you use the 12v thru cap'n method you are applying a >1v signal, so how could it drop below 1v?

And just to be sure: In the steps before when you grounded the signal or when you 12v-thru-cap'ned it, you had the sensor connected, right?

Final question: Did you switch off the engine + ignition to dis/reconnect the O2 sensor. I am always a bit afraid to (un)plug connectors whith ignition on.

Cheers
Tom

I just had a look at the wiring plan and finally I got the point. So forget about question 1.

But I would be still interested in the other 2

Tom

THANKS MR. CAP'N CARAGEOUS
 

THANKS Cap'n. for this interesting review.

I wish all the best for your an your family in the new year 2004.

Cap'n I have problems yet with the idle in my 190E. Please read my threadid dated 12/ 18/ 2003.



Mario Farias
laprefar@cantv.net

I am not sure which question is one or two but let me rephrase the concept for the record.

It is wise to not unplug connectors with circuits in operation, but it is no problem with an O2 sensor SIGNAL. I yelled that because the other two wires in some sensor connectors are heater circuit wires that carry 1-2 amps and souldn't be disconnected when powered. The 300e has separate connectors for the heater circuit and the signal wire (green) can be disconnected while running although it isn't necessary.

The lambda fuel correction circuit manages "closed loop" control. Closed loop is a control concept used for many systems but in this case what it means is that an exact mixture is maintained by monitoring the results and continually correcting. When the mix deviates rich the voltage of the sensor (the sensor is a power generator) goes high (above .45v). The system sees this and changes the EHA to lean out the mix. The sensor then goes low in voltage (less than .45v) and the EHA current is dropped to lean out the mix. All of this takes time so the actual voltage goes to .8 mabe .9 before turning around at the rich end or .2 to .1v on the lean end. This all happens more than once a second in a warmed good running system. Going down the road it probably happens a couple times a second or more (the hotter the sensor the quicker its readings change).

So, as diagnosticians we wish to see whether the controller can do the EHA control necessary for closed loop control. We will probably be doing this to a system that is not in closed loop control. The range of control at the EHA is about -12ma to +12ma (from lambda control). In reality this is not quite enough to take a car from running badly rich to running badly lean. (THIS IS IMPORTANT to realize). It is enough usually to take a smooth running engine to roughness in both directions, but it may only be enough for one direction. This is because the engine will run fine in a mixture range defined in percent CO exhaust gas of from about .5%CO to about 6% CO. Lambda control keeps it to .1%CO to 1% CO. So if you send the maximum lean correction to a car runnning 6% it may only take it to 1.5% and the car still runs great. On the other hand a car at 5% sent rich will go off badly at over 6%.

So now we have the O2 sensor disconnected. If we attach a voltmeter to it, the range of voltage possible will be 0 - 1v. This gives us good evaluation of mixture in the 0-1% CO range. It gives no idea about the 1-6%CO range in which a car will run fine.

If we monitor the sensor (while disconnected) and apply our own fictitious values to the open lead that goes to the controller we will initiate lambda control reguardless of actual mixture.

It is easy to apply 0v by grounding the lead. It is a little more complicated to creat the 1v signal but the 12v through the Cap'n method does good except you may have to replace the Cap'n with your own body as he is busy. By putting one hand on battery + and holding the green sensor to controller lead in the other hand the necessary voltage is transfered to the controller to imitate a rich signal. If one has an exhaust gas analyzer one can see the full range of correction that can take place with these maximum value inputs. This gives a view to the capability of control.

A properly set up mechanical portion of the KE system will have a mixture that can be read on the open circuited sensor. Some early systems suggested adjusting mixture with the voltage from the disconnected sensor. The mixture was set to .5-1.0v. Then the sensor was reconnected and closed loop had no problem because its capabilities could handle that base setting.

During the range observation (explained above) one should be able to get a view of this proper voltage range somewhere during the lean correction. That is the 12v through the Cap'n connection. Controller sees over 1v, interpretes a rich mix and rather slowly changes the EHA to -12ma eventually ...it takes a while .. maybe15-20sec (I'm guessing I have never timed it).

If the car was actually lean when this process starts the engine will probably die. Most often the mix is rich and so far above 1% CO that full -12ma may only get the system down into the less than 1%CO range necessary.

These are the views you can get. Getting meaningfull answers will require aquiring realistic experience of these happenings so that conclusions can be formed.

The thought of replacing this exquisite Bosch system with anything domestic blows my mind. This simple gourgeous system replaced with a crude, undiagnosible, carburator....there is real progress...not!

Steve, you have the patience of a saint. I already pointed this question to the cap'n, so you don't have to explain the same thing over and over again.

Today, I made a strange observation again. You might remember my problem from the thread AFM pot. I made a little mistake there when I sad that EHA receiceves a current of 0 to -8mA which is 8mA when the engine sounds loaded. This should have been -8mA.

Anyways, last time I measured KonEoff a stable 10mA for the first 10s then switching to a stable 20mA (19mA). This happened again today. However, as always I forgot to memorize the polarization before starting the engine and hence turned off the engine again. When I immediately turned on the ignition, I saw the 10mA for 10s again. However, then the current didn't move forward to 20mA but to -7.5mA. I started the engine, turned it off, turned on the ignition: again a stable -7.5mA after approx 10s. What has happened? And is it common that I have these 10mA first?

My other readings were:
Computer side of O2 connection grounded: 10.5mA EHA
Computer side of O2 connection Cap'ned: -15mA EHA

Computer side of O2 connection grounded: 0.95V O2 sensor
Computer side of O2 connection Cap'ned: 0.02V O2 sensor

To my understanding this proposes a working O2 sensor, a capability to control and a mixture that is not too far off to be controlled. Though I am wondering about the asymetric EHA control capability (-15 to 10mA).

My primary problem was the EHA current fluctuating between 0 and -8mA. I assume that the -7.5mA problem started today, as it never happened during my 2 measurements before. As the parts I tested today seem to work, I would assume the problem to be either fuel pressure (differential pressure in AFM, system pressure), a wrong mixture that is hard to control or something I don't know. Would you agree that if the sparks, the injection valves or the idle valve would be the problem, the rough idle would occur also with EHA off?

Unfortunately I don't have the equipment to measure those pressures. Is there anything else I can do to narrow down the problem?

I really appreciate all the time you spend to answer our questions. For me it is also very interesting to follow your logic to search the origin of such a problem. I do have an engineering background, but as you know, the gap between theory and practice is in practice far larger than in theory. And with this car (W107 SL) I am very interested to learn what is happening behind the curtain.

Thanx a lot
Tom

Voltage Readings?
 

Does anyone know what pin #3 at the service connection should read with ignition on and a fully charged battery? Battery voltage is at 12.41 with radio playing, at 65 degrees.

My readings at service connection:
Pin #1>11.48 volts
Pin #2> 0.00 volts
Pin #3> 3.76 volts >>seems low from what I've read in other posts...
Pin #4> 12.33 volts
Pin #5> 12.33 volts
Pin #6> 12.37 volts

Readings at TDC (crank) sensor plug: 794 ohms

Voltage reading at EHA plug (disconnected)> 4.14 volts

Fuel Pump Relay:
Pin # 1> 2.18 volts
Pin # 8> 12.40 volts
Pin # 9> 12.31 volts
Pin # 10> 11.47 volts

When the fuel dist. was checked under pressure, it was damp, and wet each time when depressed by thumb. Actually the stem/seal fit is loose...very loose, where the stem travels through the adjustment/locking cap. Maybe someone rearranged this fuel dist. before I purchased the automobile?.....the locking washer showed evidence. If I need another fuel dist. for parts (to obtain correct fitting to the stem locking cap), would someone have a bad fuel dist. for parts? Will make more tests tomorrow and post them here. Thanks for everyone sharing info, especially to Steve
:D !

Any Luck Cap'n?
 

Hi Cap'n -

Any luck with your 300E lately? Wondering how your progress is moving along. I now believe that my FD is the culprit,and when I get some pictures posted for Steve (should be tomorrow) please take a look and see what I am talking about.

FD replacement and ruling out the fuel return line as a problem are just about the only things I can do at this point.

Would like to hear from you. Your PM folder is jammed up by the way. :D

My lack of expertise in Bosch KEIII diagnostics is now legendary, but I like the term "Capn'ed" to describe generating current for the O2 sensor circuit!!;)
Here is what I do know, my car needs the wiring harness replaced before I can get any consistency in readings. I know this because when my car is in it's failure mode I can grab the harness near the controller and it will run good. Also with the KOIO I can grab the harness and hear the fuel pumps engage.
Now, with that said, MY problems may not be remotely connected with any of the others stated here.
StevebFL is the expert here. However, not understanding the system unfortunately prevents me from understanding his commentary. The more I study this system the less I seem to understand it. I'm hoping that the wire harness is the reason my test results are so confounded.
I'm an old dog, but I hope I can still learn (and understand) a new trick or two.

wireharness
 

The wire harness is a real pricey bit isn't it? Replacing it is going to take a while too.

When I do any tests on my car I always check all the connection to the CFI computer to make sure a wire is not causing the problems, it takes a bit, but is well worth it and if you were to take a look at my wireharness, you would see that it is not in the best of shapes, but I fix what I can, solder here, some new wire there, as long as the main lines work, the car will work.

As for KE, believe it or not, but I think yesterday was the first day I finally understood what all the experts meant when they said that the lmbda voltage should fluctuate when all the controls work correctly.

I used a really low quality multimeter set to 10V range, and looking at it closely, I did finally see how the voltage goes up and down, bounces basically, not very fast, but it does, this was also an analog MM, not digital, the digital one tends to miss a few values and then you don't see the pattern. At the same time I had another MM hooked up to the EHA to monitor the current, and sure enough, the current also follows that same pattern, up and down up and down. A beautiful sight on a 19 y/o car :)

xp

Re: wireharness
 

I have a harness from a salvage vehicle. It will require 25 splices but all the sensor connectors are there and appear to be in good shape.

As far as that last statement, that's something I have yet to see. I'll bet that IS a pretty sight though.

splicing
 

Cap'n

Make sure to get some heat shrink tubing for the spliced harness, it will keep it in good shape longer. Don't use the black insulation tape, it falls apart with the least bit of heat and we all know there is plenty of that in the engine bay.

I'm sure you'll get the car running :)

xp