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  #1  
Old 06-20-2010, 09:57 PM
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Irregular readings EHA and Oxygen sensor

I am sorry if i am repeating what someone else asked but i've looked through 50 posts and have not seen a answer yet.

The car is a 1990 300E 4matic, i was trying to read the mA to the EHA with ign. on the other day and it showed 18.78mA spec should be 20mA. But while the car idles it seems to stay around 0 to +1.5mA but never goes negative. So once i saw that i decided to test the oxygen sensor and the volts fluctuates all over the place. Also while WOT i only get about 8.78mV never goes full rich. I have checked for codes and none have come up as well. Is this a sign of the eha being off spec i tested the ohms and its within spec 19.5ohms and no leaks. Oh and yes i have checked for vaccum leaks and repaired a few in the car but from here can't find anything else.
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  #2  
Old 06-21-2010, 08:19 AM
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Sounds like that is working very good for a 20 year old car to me.

Are you having a problem?

You would have to adjust the mixture tower to make it go negative.
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  #3  
Old 06-21-2010, 09:40 AM
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Its more on a account for the MPG i get which is around 16mpg highway and car seems a bit slugish at times,Such as going up hill not a turtle but feel like it needs too much accelertation. Indeed this is a mechancal injection and no where comparable to electronic injection still feels sluggy. The fuel filter was replaced and all the screens such as the one attached to the feed on the gas tank, the inlet on the FD were cleaned also the eha screen. Also just put new injectors because of 2 squirting and not spraying properly. I used a test by the mercedes manual to check FD flow and it seemed to be ok. The voltage to the eha and o2 do not seem low to you?? almost like its working on 85% of its capability
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  #4  
Old 06-21-2010, 10:27 AM
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IF (since) the O2 sensor is controlling the mixture, adjusting the mixture to the lean won't accomplish much in regards to fuel mileage.

Only when cold OR under full acceleration will the car actually use any more fuel as it is now set..
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ASE Master Technician
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44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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  #5  
Old 06-21-2010, 07:49 PM
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Thats unless your catalyst is clogged?
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  #6  
Old 06-22-2010, 08:20 AM
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Very rare condition on that model, unless it has an aftermarket catalyst.

Have you tried adjusting the mixture toward a lean (negative) reading.
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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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  #7  
Old 06-22-2010, 04:49 PM
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I have, however i have been fidiling with so many things i am going to reset the ecu and drive th car a little and see what happens. Out of curiosity how should the O2 sensor be acting while idling normal operating temp is there a certain mV range? Also during cruising some type of range?
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  #8  
Old 06-28-2010, 11:04 PM
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I reset the ecu and checked the codes again i am gettin an intermittent code 2 wide open throttle switch, Also i had the air filter removed and spuratically the plunger would go down and the rpm would raise for a second then back to normal? any ideas even at one time had the plunger almost like flutter as i kept a constant rpm towards the 2000rpm range. Accumulator? Oh also the car will not start the first time in the morning. second yes it does but seems to be working on 4 or 5 cylinders for a second then clears and runs ok. After the first start the car starts ok but seems to struggle to keep a constant rpm instead it starts rpm goes to 1300 and goes back down to 600 then rises.
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