My 1990 300e w/103 engine appears to have a bad ECU. The car is hard to star and will not idle. Once warm. It will run. There is no current or voltage to the ICV or EHA. Zero duty cycle on pin 3 of the X11 connection. No Check engine light. I have check the OVP relay and it is operating properly with good continuity.

Are there any other checks I should do before I condemn the ECU?

A few of us here have bought replacement ECUs from www.car-part.com. We all payed about $50. Problem solved.

Mike

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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E

For $50 I'll try that trouble shooting method.

As cars age probably one of the most common problems is connectors. This is especially true of low voltage connectors that are part of the various electronic control systems.

Remove the connector from the ECU and carefully check all the pins and receptacles with a magnifying glass. Look for bent pins and corrosion. Scrape off any corrosion with a dental pick or Xacto knife. Then clean everything with contact cleaner.

Sometimes just "cycling" the connectors will solve problems, but a thorough inspection of all engine control system connectors including the ECU and all sensors and actuators will usually be beneficial.

Duke

Thanks I'll give that a try. I have hit the contacts with electric contact cleaner several times, did notice that the contacts have what look like a film on them. This car came from Florida east coast and salt air envioment.