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Old 09-18-2002, 02:48 PM
Posts: n/a
The "listings" I referred to were three different service manuals: an aftermarket book on Bosch CIS, a printout from Haynes that they sent when their original publication proved to be lacking, and the CD rom copy of a Mercedes service manual.

I have a somewhat functional knowledge of automotive electronics, and even german-style electronics, where pins labeled 30 are always on, 15 is on with ignition, etc., having been at one time certified by VW in automotive electronics. THe problem with a rational application of Ohm's law is the requirement for knowing two of the three variables, and Mercedes seems to only provide one, leaving the technician to either perform blind testing or guess at the other variable.

I agree that testing the devices individually is best, but having one method in one book and another somewhere else is aggravating. If I assume, based on provided information, that the 8 volt value uesd internally tot he computer is also used for power to sensors, well then we could establish a current amperage through any known resistance, right? And knowing the desired amperage at the EHA unit, we could establish what the resistance of the EHA should be, and possibly establish how much energy is required to move the EHA coil against a given fluid pressure, right? THen, if we knew the logic diagram for the system, we could see how the various sensors (inputs) and motors or coils ( outputs) interact, making the diagnostic process one step better than "push these buttons on the tester, get these values or replace the parts."

If I sound frustrated, it's because vehicle manufacturers seem reluctant to give diagnostic authority or education to their front line, the service technicians. This seems especially true of the information provided to non-dealer techs, though I remember a lot of "do this" and "change that" when I was a dealer tech on the late 70's and early 80's.

I will look again for drop-outs or dead zones in the potentiometer. I rashly thought that if it worked at the ends there needed to be continuity. I still wonder about how being above the specification limits affects performance. How many milliamps to the ohm at 8 volts?

If anyone is still reading at this point, I used the 8mA target for a standard temperature engine as my method of adjusting the idle mixture after changing injectors. At that setting, Cold start is less than desirable, maybe 5 seconds cranking at 60F air temp, and stumble for about 30 seconds after starting. I still have about the same 1/3 throttle limitation for real power, but the engine will not die under wide open throttle. I even saw 70mph on a flat stretch of highway, where before I was limited to about 50. Having fun now
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