190E 16v High Idle, cannot rev over 2500rpm - Page 2 - PeachParts Mercedes-Benz Forum

JimSmith · #16 04-12-2008, 10:18 AM

Pentoman,

That was a very informative overview of the KE-Jetronic system. While the write up completely ignores the "tower" adjustment, it does have a key sketch showing the EHA and the air mass sensor/rheostat arrangement, including the "tower" adjustment. I studied the overview on the link you provided and have a basic grasp of the system's function. It appears to be something only a German could invent as it fits an old German idiom to a tee - "Why make something simple when it is easy to make it complicated?"

In truth it is likely due to the learning curve for microprocessor integration that gave us this system which seems to have undue mechanical complexity as well as a bunch of electronics that is now obsolete.

Here is an excerpt from Page 20 of that manual you posted - unfortunately the size limits for this site make photos of decent size and resolution an unnecessary challenge. It shows the fuel from the pressure regulator coming in the port labeled "2." It is somewhat misleading but that port feeds the fuel pressure regulator pressure to the upper chamber of the pressure balancing chamber identified as "7" by going through the throttling device in the center (item that moves up and down when the air mass sensor is deflected) and to the EHA assembly on the right side of the sketch. There the adjustment feature is not shown, and there is a spring at the lower right that preloads the system to achieve a zero current bias with the permanent magnet that is part of the EHA electro magnetic circuit described on a prior page of the manual. Anyway, current in one direction pivots the little plate at the pivot point marked with the bullseye/arrow going into the page in a specific direction.

When the top of the plate moves towards the nozzle of fuel supply it adds flow resistance and that causes the chamber around it to lose pressure as there is always flow out port "6" which is the return line to the primary pressure regulator and back to the tank. When this pressure drops the pressure below the diaphragm in the pressure balance chambers, area "9," also drops. This deflects the diaphragm downward, opening the port to the injectors themselves and they see the pressure that is a result of the regulator pressure below the throttling edge of the slotted plunger, and the flow rate the plunger's positon dictates. The system is set up so that between the springs pushing the little diaphragms upward to shut off the fuel flow and the EHA pressure regulator function, at idle there is something like a 0.4bar difference in pressure between the upper and lower chambers, with the upper chamber at the higher pressure. When the EHA pushes the little beam or plate away from the inlet nozzle, the pressure on both sides of the diaphragm is the same and the spring force jams the diaphragm sealing surface into the bottom of the port leading to the injector, and fuel is shut off. I hope that helps and is accurate.

The "tower" adjustment is shown as the set screw on the left side of the arm that holds the moving part of the rheostat. This appears to be a mechanical alignment capability, and I don't understand what happens to them to make them go out of alignment. Seems like one of those things that should not change, ever, once it is set. Anyway, you can see that screwing the setscrew inward (presumably clockwise) you will displace the moving part of the rheostat and likely move the center plunger a tiny bit. I believe the geometry of the system is trying not to do that, but it looks inevitable to me in the sketch. Anyway, that rheostat position is an input into the current value being sent to the EHA that adjusts the pressure balance to either increase or decrease the fuel pressure going to the injectors.

It sure seems to me that once you have an O2 sensor feedback running this stuff should be pretty rock solid and independent. No 02 sensor, as in my son's car and things can be a problem.

Thanks for posting the manual. Jim