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Old 08-22-2003, 05:54 AM
Registered User
Join Date: Jul 2003
Posts: 90
Mr. ctaylor, Mr.Stevebfl

Thanks for your threads.

Please, I need your help.

My 190E, 2.6 L, 1988 has a lot of problems.

The Voltage out going from O2 sensor is 0.8 V. I suposse that it is OK.

The Voltage to the O2 is the same thart the battery almost 14.0 volts. I suposse that it has to be 50%.

The voltage in the in ping Nē 3 of the socket is 14 V, same that the battery. Messured with the DUTY CICLE is 100%.

The gas milage is too bad, almost 4 kilometers per liter.

The RPM in idle is 900 but when shift to Drive lost almost 300 RPM.

I'd appreciate your recomendations.


Mario Farias
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Old 08-22-2003, 05:59 PM
Super Moderator
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,315
Where did you measure the output from the sensor?

It sounds like the ECU is not getting a signal from the sensor, thinks that the mix is lean, and has gone to full enrichment. The manual suggests that the O2 sensor wire has a short to ground.

But that would not explain your miserable gas mileage. I don't think even 100% enrich can drive it that low. It seems to me that either your mixture adjustment was totally botched, or you may have a problem with your fuel distributor. There a lots of posts by Cap'n Courageous on this.

Can you get your mixture adjusted by someone with an exhaust gas analyzer and see if that improves the mileage without screwing up the idle or performance?
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 08-23-2003, 11:46 AM
Posts: n/a
4km per litre?

Yikes.That's really bad, looks like your mixture is way off.

Your O2 sensor may be bad but I have yet to see a post that reports that bad a mileage from a faulty O2 sensor.

How does the car perform?

Smokes?Hesitates severely from acceleration?Heavy exhaust smell?I'm curious.Is the car driveable at all?

Ctaylor is right.Get the mixture sorted out.

If you are a DIYer, disconnect the EHA and see if the car performs better.

If it does, it is more likely a sensor that has gone bad eg O2 sensor, EHA, etc.

If it is the same, then one of the mechanical components may have gone bad eg fuel pressure regulator, fuel distributor, etc.

With the EHA off, the car's mixture can be tuned to run mechanically well, independent of the sensors.

The only problem you will have is cold hardstarts coz with the EHA off you get no cold start enrichment.
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Old 08-23-2003, 12:21 PM
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Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
4km per liter? I'm not sure if that is even possible if all the fuel is getting to the cylinders, perhaps it's leaking out somewhere, or is not getting even burnt completely.

Can you give us any more details about how the car runs? I think that is where we should start, and once we have an idea of what might be wrong with the car, we can proceed to voltage readings etc...

1985 190E 2.3L - a constant project.
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Old 08-25-2003, 11:20 AM
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Join Date: Jul 2003
Posts: 90

The 0.8 volt from the O2 sensor was from the only cable coming from the O2 sensor, down the plastic cover in the passanger side.. It was taking with the car turn on and warm, almost 90 ēC. We notice that increasing the RPM with the accelerator the voltage changed from .5 Volt to .9 volt.

The voltage going to the O2 sensor was taking from the flat socket that has the positive cable and the ground. The voltage was 14 voltios almost the same that the battery voltage.

The car runs well, I think. It has power and take the overdrive as fast you ask it.

The signals gotten form the round test socket in the pin number 3 was 14 volts, same that the battery and 100% mesuared with the DUTY CYCLE. It was impossible to get 50% with the 3 mm allen apllied on the mix screw.

Do you think that O2 sensor is bad even thougt it produce a voltage of 0.8 volts?

Why the voltage on the sockect test pin 3 is constant the same that the battery, 14 V., or 100% DUTY CYCLE.?

Why dont get any voltage change in the socket test pin 3 moving the mix screw with the allen 3 mm?.

Why it lost 300 RPM when shift from NEUTRAL to DRIVE.? Also when conect the AC the RPM descend untill 500 RPM.

How to test the EHA, & TPS ? Thanks. MARIO FARIAS
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Old 08-25-2003, 12:11 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Disconnect the O2 sensor. The duty cycle should read 50%. Key on, engine off, should give 70%.

Use those figures to calibrate your test technique. if you don't get those numbers you are either testing wrong or you have electronic control problems.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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