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  #1  
Old 01-31-2003, 07:27 PM
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trying to understand the right eha reading

steve i have a 92 190e 2.6 do i set the eha ma to .2m to.3 ma or the .8ma last night i set it at .6ma today after work it read .9ma
my o2 sensor is jumping from.10mv to .75mv constantly back and fourth .thanks for your help
re-read article is mine positive or +/-



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.


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Last edited by josev; 02-01-2003 at 03:29 PM.
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  #2  
Old 02-02-2003, 10:11 AM
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92 would be +/-

all cars made in 86 and up have it this way.

so 0ma is your middle point, if O2 is jumping, it might need to be checked or replaced, depending on what you mean by jumping.

xp
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  #3  
Old 02-02-2003, 06:52 PM
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O2 is jumping, it might need to be checked or replaced, depending on what you mean by jumping.

that when i read the o2 sensor the voltage flutuate back and fourth from .42mv to .71mv or .45mv to .66mv at idle
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  #4  
Old 02-02-2003, 07:15 PM
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The O2 readings of low .1-.2v to high .7 to .8v are what you want to see and will occur at any EHA reading that is in closed loop. One must understand the concept of closed loop. Closed loop infers control. Control is accomplished by going rich when reading lean and then turning around and going lean once rich is recognised. Where ever the mechanical mixture is set the system will move back to lambda by using the current correction. If it takes 4ma then it will hover about that. If it takes 8ma then it hovers about that. It should not change much once everything stabilizes and the O2 sensor cleans itself.

The way to judge the appropriate average EHA current is to disconnect the O2 sensor and view the current. All six cylinder models centered on zero with plus and minus current capabilities. The the early 4cyl models only corrected with current in the positive direction and in order to have both lean and rich correction they needed to start above zero. Thus 8ma is right for them. If one disconnects th O2 then the current will be either zero or 8ma at idle.
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  #5  
Old 02-02-2003, 07:42 PM
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ok so i'm in the ball park eha reading from 0.0mv to 1.32mv
flutuating back and fourth at idle and when i check the duty cycle on pin 3 of x1 it flutuate from .48%to.53% dutycycle then when i rev up the engine and it comes back to idle the dutycycle stays at .50%
for a few seconds then it goes back to doing the flutuation
.48% .53% $1400 for a rebuilt fuel distributor put a hurting in my wallet but it fix my rought idle and hesitation
thanks steve took a while but i got it
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  #6  
Old 02-02-2003, 07:53 PM
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"ok so i'm in the ball park eha reading from 0.0mv to 1.32mv "

Everything else works but this statement. EHA is measured in CURRENT not voltage (mv) so I can't compute.
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  #7  
Old 02-02-2003, 07:58 PM
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steve i meant ma. my apology
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  #8  
Old 02-11-2003, 08:45 PM
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Picture

Can anyone post a picture showing how the current on EHA is measured?
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  #9  
Old 02-12-2003, 01:52 PM
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Click on D.I.Y. on the top bar then click on Evaluating Electronic Engine Controls.

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  #10  
Old 02-12-2003, 08:16 PM
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Confused

Ok, I bought a DMM with duty cycle measurement. I connect the positive to pin#3 of the diagnostic X11 terminal, and negative to ground. I read a duty cycle that oscillates between 29%-35% at idle. The article in DIY states a slightly rich mixture at 35%, hence I assume I am running rich.
Here is the catch, in another website: [URL=http://pages.prodigy.net/jforgione/MB_Lmbda.html], the graph states a LEAN mixture to anything on the right hand of the graph (below 50%).
Am I lean or rich?
I have attached the graph for illustration.
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trying to understand the right eha reading-airfuel.jpg  
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  #11  
Old 02-12-2003, 09:27 PM
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Anyone?
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  #12  
Old 02-13-2003, 10:00 AM
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You are not quite seeing the picture. The illustration you present is a graph of mixture. The point of the graph is to show the area that must be found through fuel control.

What you aren't realizing is that when you are "IN CONTROL" you are in a state of manipulation where the mixture is held to that ideal area. "In CONTROL" means that the same mixture is had at 20% as at 80%. The difference is the remaining ability to correct.

All of this control is on top of the mechanical/hydraulic system that really does all the work. The difference between 20% and 80% is in the state of the mechanical/hydraulic decision. Whatever that decision the electronics tunes out the right mixture as long as the base mixture is within the correction window.

The reason I suggest 35% say, is that all mixtures done closed loop and all instantaneous mixture changes are done with the mechanical/hydraulic decision. I prefer slightly rich in these situations. Remember that once warmed the closed loop system keeps the mixture dance at exactly the same point in any steady state (the rich lean correction takes around a half second at best so steady state is anything happening slower that that).
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  #13  
Old 02-13-2003, 11:31 AM
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Thanks for your reply.
OK, I sort of get it.
Now, lets say I turn the screw for the idle control mixture to make it leaner (assuming I am running rich at 32% average duty cycle).
Would doing so will make the duty cycle go to 50%?
(Engine at normal operating temperature and idling)
If it does, then I assume that the closed loop control will keep it dancing between about 45-55%.
I am just trying to figure out whether I am running rich or lean, and how to adjust it using the duty cycles from the diagnostic terminal.
By the way, if you happen to have the list of codes-duty cycles and what they mean, please post it or send it to me.
I find the codes but there is allways a note stating "for vehicles from 1992 and newer.
Mine is a 1986 300E
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  #14  
Old 02-13-2003, 05:22 PM
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Yes! Now you have the picture. Every move you make with mechanical/hydraulic control is sensed and corrected for up to the extent of control.

Your car only has the fixed duty-cycle codes. If you are getting these duty-cycles you have no codes. To see a code, an example is 50% fixed. This is the code for O2 sensor. It appears untill the sensor is hot and generating its voltage signal.

There are codes in the archives. I don't have a list that can be attached.
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  #15  
Old 02-13-2003, 05:43 PM
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Thanks for your help.
I have read almost all the posts about this, and still have questions. But I know it is hard to explain things over a post in the internet.
Since I drive very often up and down I-95 (from Florida to NY), one day I'll try to contact you when I am in FL, perhaps we can talk over a cold one.
Hopefully this weekend I'll pop the hood, take the air filter out, and play with the screw until I get the 50% duty cycle.
For me is hard to work on the car, since I live in an apartment complex where it is a big NO-NO to do mechanical work in the parking area. They only allow things like working on flat tires.
So I take a couple of tires OFF and open the hood
I can't wait to own a house with a garage.
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