1-stay away from the eha. it does have a function but NEVER fails other than leaking fuel out of the pins into the connector. never had 1 cause a running problem unless someone messed with it.

2-you have to have a fuel pressure tester and the ke-jet testing is different than k-jet. without knowing pressures, you can't diagnose the problem. iirc, upper and lower chambers are .4 bar apart when hot. if they are the same pressure upper and lower, it will run lean. i suggest you google mercedes ke-jet testing and look for the 124 or 201 manuals as they would have complete info for testing. being a gray car, the us specs will be ok for you, just not perfect. i doubt the difference will be a problem. getting gray specs is the problem i see.

3-you also need a volt meter or 2 as you need to watch amperage at the eha, easy to make special harness, and on the 10 pin connector to watch duty cycle. i use 3 so i can watch to o2 sensor, also. that testing is in the manuals.

i worked on 1 gray 103 engine 107 and it had a running problem but it was ignition, not fuel. not a lot of help there. i will say i enjoyed that car more than the heavy v8s we got to drive. much better feel. good luck, chuck.