Duty Cycle Madness

[LloydMd]

Hello,

I have a 1990 300se/ M103 engine. I bought the car with a blown head gasket which I repaired. For the last year I have been doing routine maintenance as is the standard for these cars. Thus far I have put about 8,000 miles on the car and the odometer reads 189,000. I need expert help.

Either as a preventative measure or due to failure, I have replaced the following with Bosch/first quality parts:

Plugs, wires, and distributor cap and rotor
Injectors, holders, o-rings and seals
Fuel pump, fuel filter, and deteriorated rubber gas lines
EHA
OVP
All deteriorated vacuum hoses and fittings

Currently, the engine measures 16 inches of steady vacuum and the gauge behaves normally when revving the engine. With my old EHA the duty cycle was around 65%. When I put the new one on I adjusted the duty cycle to about 60% by adjusting the mixture. Through all this, the car seemed to run fine. I periodically check the duty cycle and for the last month or so, the duty cycle reads 98% at operating temperature. When the engine is cold enough, it will start at 50% as it should, then the loop opens and it will show a normal duty cycle, then as the car warms further it will quickly run up to 70, 80, 98% and stay. It does all this with the usual decrease in idle as the engine warms. In all other aspects the engine runs normally. From the dash tachometer the car idles at about 750 in park and 600 in gear. The idle is no rougher than what I have been told is normal for these cars.

Now, I am aware of the relationship between the fuel distributor pressures and the EHA and the throttle mixture. I do not have the equipment to measure the upper and lower chamber fuel pressures and I am reluctant to mess with the EHA since so far I have only touched the mixture and it was OK at the time, and the car still seems to run fine. So, what could be the reason for the high duty cycle readings and why does the engine seem unaffected? Any ideas will be greatly appreciated.

Thanks,

Lloyd