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Old 03-13-1999, 02:35 AM
Posts: n/a

I Originally posted my problem in and will try to explain more clearly what my problem is.

The car is a 1988 300E with 120,000 miles on it. I recently checked the fuel injection system because it is due for inspection. I used my Fluke 88 tester which has pulse/duty cycle setting, plugging it into the test socket X11. My understanding is that if the value moves within a range between approximately 38% to 42% the system is functioning properly. But if the value stays on a specific number that is the number (or code) of the problem, these numbers being listed in the engine repair manual.

In my case from a cold start the reading is a constant 50% until the engine warms up. When the operating temperature is reached the number starts to move between 38% and 42%. But if I drive the car and stop and take another reading the number is a constant 60%. If I then turn the engine off and immediately start it the reading returns to a correct range between 38% and 42%. If I again drive the car the same results occur.

I have two different listings of duty cycle readings (codes) and neither one shows 60%. I have cleaned the contacts on the control box as well as the various sensors on the engine. I have also replaced the oxygen sensor in that the old one was three years old and figured I would have a good starting point. When the duty cycle reaing is within the correct range unplugging the coolant sensor results in a reading of 30%, unplugging the oxygen sensor results in a reading of 50%, and the altitude sensor a reading of 80%. But when the I am getting a reading of 60%, unplugging any of the sensors I just mentioned doesn't change the reading.

I hope I explained the symptoms clearly, I have started to test each individual sensor but so far have found nothing abnormal.

Thank you for any assistance you can provide me with.