My on/off ratio on my '81 380SL sits stubbornly at about 10%. This occurs whether the engine is cold or hot and does not change with RPM. When the engine is cold, it should read a constant 60%.

In addition, the air pump does not engage.

I have verified the following:

- the control unit is getting 12V
- the control unit is grounded
- the O2 sensor is putting out .4V
- the oil temperature sensor is working correctly
- the throttle switch is working correctly
- the frequency valve does buzz

Adjusting the mixture has no effect on the ratio.

The car is running well and getting reasonable gas mileage.

My conclusion is that the lambda control unit is dead. Any other ideas?

TIA

__________________
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