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Old 07-26-2004, 10:30 PM
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Join Date: Jul 2002
Location: Ojai, Ca.
Posts: 88
M103 EHA Adjustment

I've been troubleshooting a hard start problem. Through the course of regular maintenance, I have replaced the fuel pump, accumulator, filter, injectors, and O2 sensor. The system pressure is 5.5 bar and the lower chamber is 5.1 bar. I checked the cold start valve and it functions properly with no leaks. The EHA current and resistance as specified by the manual for all conditions was verified. Coolant temperature sensor also reads properly at cold and normal operating temperatures. Also replaced and successfully adjusted the airflow potentiometer by referring to other posts on this site. This change dramatically improved the starting problem but did not eliminate it.

I was reading in Stu Ritters "E-Class Owner's Bible" that some compensation for normal wear of the fuel distributor can be made by adjusting the lower chamber pressure using an adjustment screw on the side of the EHA. I haven't checked for the location of the screw but the pressures that Stu was calling out don't correspond to my pressures. He suggests going from 4 bar to 4.5 bar on the lower chamber. I'm already at 5.1 bar. Does this adjustment apply to my car (1990 300 SEL)? I'm looking to see if some tuning will solve my problem before I invest in a cold start valve and/or EHA.


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Old 07-26-2004, 11:33 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,233
Have you checked the "duty cycle"?

If not, go to:

and print out the instructions. The duty cycle is only applicable to closed loop operation, but the basic setting is the basis for the open loop mixture when the engine is cold.

A lower duty cycle at idle means a slighty rich basic setting, and I have found that about 45 percent at idle gives good cold starts and warm up characteristics.

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Old 07-27-2004, 09:56 PM
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Join Date: Jul 2002
Location: Ojai, Ca.
Posts: 88
Thanks Duke.

I usually set mine at 50% but I will try your suggestion and see how that effects the cold start.

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Old 07-30-2004, 03:25 PM
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Join Date: Jul 2004
Location: houston
Posts: 24

How do you check if FD is working? I have 1990 300E, I can't start ( cold or hot) except when I pour little gas in air intake. I have replaced accumulator, pumps, relay, cap &rotor.

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