560sel EHA issues - PeachParts Mercedes-Benz Forum

Two560Two · #1 10-01-2013, 08:00 AM

The EHA developed a fuel leak on my vehicle, I removed it and found a hairline crack on the back side of the unit. I bit the bullet and bought a new Bosch EHA. GOt it yesterday and installed. To my surprise after installation the car was idling rough and any gas you give it the engine would stall. I also noticed the ball missing off the CO mixture adjustment tower indicating the previous owner had tampered with it. Anyways after checking all my vacuum lines which are ok and connected properly I proceeded to adjust the new EHA by removing the small screw behind and turning the small hex in increments. I had to do this several times. The engine now runs ok but when hot and you shut of then restart the idle becomes loopy and any sudden application of the accelerator from a stop the car dies. If you feather the gas then it will be fine. Is it suggested I check & adjust the lambda on my car? I found a useful write up on how to do this by using a meter with the o-scope function.

JamesDean · #2 10-01-2013, 09:31 AM

I believe the proper procedure would have been to leave the EHA adjustment alone and adjusted the lambda tower.

I would recommend you do that. You can use a o-scope, or a meter that can read duty cycle. Connect either up to the X11 port (pins 2/3 I believe, I cannot remember polarity) and adjust it to near 50% I believe. You want to make sure that you have approx. the same % at idle AND higher rpm (either 1500 or 2500 I can't remember either.)

Here is a good write up.
BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT

The ONLY way to properly adjust the EHA is with a fuel gauge set (70-90$). IIRC you set the EHA so that the upper (or lower?) chamber is 0.5 bar less than the system pressure. Its been a while since I've done this but that was the general jist of it. You can read more in the FSM. I believe its under section 07.

Two560Two · #3 10-01-2013, 09:49 AM

Thanks and that was the write up I was referring to. I just tried to do it now but my nice meter broke. I checked the fuses and the battery with no go. All I have for now is just a regular meter with no O scope function. In any case I have already tampered with the EHA adjustment. I will try and get it back to where the mixtures should be

Elektri · #4 10-01-2013, 11:21 AM

The EHA is sort of like how you play tennis with the racket out in front of you in the middle - should the ball come to the left or right, your racket is in the "center" and can then swing either way.

Same with the EHA - it needs to be adjusted in the "center" so that it can in-turn adjust more rich or more lean as it receives a positive or negative electrical current from the analog computer.

All of this is a "balancing act" depending on fuel pressure and the pressures in the upper/lower chambers of the fuel distributor.