I m sorry I see what you mean now after reading the r17 explanation. I was under the impression however that mercedes cars don't have both...I thought that some cars had r17, some had r16, and they both did the same basic thing...adjusted ignition timing. Are you sure you have both? If you do have both in your car, I assume the r17 does the same but with respect to fuel?? Maybe not, but CIS-E (r17 trimming) is not only ignition while EZL (r16 trimming plug) is.

__________________
1985 190E 2.3-16 Euro