The way you check a system.... any system.... is to understand what it does and montor the function.

In your case, the EHA is the sole electrical component of fuel control. Control is accomplished by sending a small current through the device which causes a calculated leak of lower chamber pressure to be effected. This effect can be monitored and has given specifications. The current has a definite profile. EHA current during starting is around 50ma, cold running around 10-20 (depending on temp), add the two if one is starting cold.

Once warm and with fuel mixture proper the EHA current goes to zero! If it wasn't zero one would adjust mixture till lambda control hovered about zero. Lambda control with a good sensor will go lean until rich correction and visa versa. That sweep should eb 3-4ma. A sudden acceleration should cause a 2-10ma (positive) corection due to the airflow potentiometer.

If you ground the O2 sensor lead the EHA will go to 10-13ma positive enrichment. If you place one hand on a 12v connection and the other on the O2 sensor lead the opposite will take place and the EHA will go -10-13ma. Thus the whole of O2 sensor control is from -13ma to +13ma or maybe a little less (some cars go further than others but will be consistant at whatever your are exhibits).

If what you see doesn't look like that then you need to figure why. If it looks like that and has an issue you need to evaluate whether the current does the proper thing to the lower chamber pressure. The lambda control will make about a .2bar difference in lower chamber pressure from rich to lean. The differential pressure (the difference between upper and lower chambers is about .4bar so lambda will change it from .3 to .5 (or a .2bar range).

If that isn't the issue then one must run the individual distributor outlets including injectors through a differential flow meter at three different flow rates with less than ten percent difference cylinder to cylinder at each flow rate.

Of course it could be ignition related.........................

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician