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  #1  
Old 03-08-2001, 12:50 AM
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as I have posted before, I have had some hesitation on my 87 300E whenever I accelerate from a stop. I found this page on the MBCA website the other day and tried it out; http://www.mbca.org/MBCA_Rough_starting.htm
I simply spliced and soldered in a 470 ohm resistor in series with the engine temp sensor. now the car starts right up and takes right off!
Adam

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Old 03-08-2001, 09:46 PM
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This quick fix was withdrawn by Mercedes in later years because of the emmissions it produces. The resistor just makes the engine run a little richer.
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  #3  
Old 03-08-2001, 11:21 PM
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Its amazing that the car club pays so little attenion to their published fixes.

Overwhelming the fuel system to overcome your problem may be the cheapest way but it would get us professionals a $10k fine.

The resistance of the temperature sensor is non-linear. To get an example of the way what you are doing affects the system here are the values. They are semi approximate. When cold the sensor has about 2000 ohms resistance. The addition of 470 ohms is say a 25% increase to the richest running conditions. When the car is at 180 degrees the sensor is around 200 ohms. Now your fix is modifying the sensor value by over 200%.

During early EFI, Porsche and VW added a 200ohm resistor to their very similar temp sensor. The whole point (during an era where mixtures were 10 times higher) was to alter hot restart conditions. The point of this fix was that they could make a significant change in hot conditions without making much difference in cold conditions. This is also what this fix will do. If you are effecting your problem cold imagine what you are doing hot.

You are masking the problem. If your car was a year or two newer It would tell you about it with a check engine light.
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  #4  
Old 03-09-2001, 12:56 AM
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Temp. sensor...

I agree with Stevebfl that this is a poor fix. Your temperature sensor may have become defective, however, and could be causing your original problem. I had a similar problem on a GM vehicle - the resistance of the sensor was supposed to be around 7500 ohms at 40 degrees, but when I checked it it was only around 2000 ohms at 40 degrees, which made the engine run way too lean on a cold startup. Replacing the sensor took care of the problem. The hot resistance of the temperature sensor is very important, as Stevebfl mentioned, as the temperature sensor is one of the primary fuel control inputs to the computer. I don't have a chart for the M-B sensor, but on a GM sensor the resistance at 210 degrees should only be 185 ohms. Adding 470 ohms to the 185 ohms would make the engine run as if the choke were stuck on all the time, a bad scenario for you and the engine both. This could affect your fuel mileage by as much as 30 percent. Sensors are easy to test, all it takes is a pan of water, a thermometer, a burner and some ice cubes and an accurate ohmmeter. If you don't want to bother testing it, my suggestion would be that you purchase a new sensor and install it.
Richard Wooldridge
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