EHA Current 560SEL W126
 

Hello.

I live in Málaga (Spain), my car is a nice 1990's 560SEL.
I've search on internet for days trying to find an answer to this problem and found nothing. I've asked a few mechanics here in Málaga, but this kind of injection (KE-jetronic/CIS-e) are very difficult (unknown I think) to repair, even at mercedes garage.

The problem is that the current sended to the EHA is not correct.
As I have read, normally this current is changed due to the O2 sensor to adapt the mixture, my problem is that my car is an EURO, 220 Kw, an have not lamba nor KAT, so I can't read the duty cycle or made any corrections on the current sended to the EHA adjusting the mixture screw.

The current measures I made are this (in Ma):
Contact on, engine off: +75.
Engine idling at 30ºC: +20.
Engine idling at 80ºC: +3.
Engine at any rpm except when idling(30ºC): fluctuates about +10 decreasing, as the temperature raise.
Engine at any rpm except when idling (80ºC): -8/-10. (On road, driving fluctuates -4/-10)
Wide Open Throttle: +4/+6.
Deceleration fuel cut off ( driving at more to 1600 rpm throttle unpressed): -50.
The current at 80ºC should be, according to MB, fluctuates between 0-> +/-3 Ma. at any rpm.
Pressure test is:
-- Idling: 6,3 BAR at upper chamber and 5,9 at lower chamber (current at EHA +3 Ma).
-- Pressing the throttle: same at upper, but lower chamber raise to 6,0 BAR (current at EHA -8/-10 Ma).
Always must be a difference between the chambers of aprox. 0,4 BAR, the negative current reduce the differential pressure to 0,3 BAR, makes the mixture to lean and the car hesitates a lot arround 2/3000 rpm.

I think that the hesitation could be an ignition problem, but disconnecting the EHA or the AFM pot, leaving the pressure differential steady at -04 BAR, the hesitation dissapear, so must be a injection problem.

Adjust the EHA screw is not the point, because the diferential pressure is OK.

-- I tried another ECU, and the current measures are the same, so the ECU is OK.
-- I changed the AFM pot for a BOSCH new one (pretty difficult to find), adjusted to 0,7 volts between pins 1&2 at idle, and the problem still there.
-- The temperature sensor is OK (resistance measures according exactly to MB specs).
-- TD signal measured at fuel relay (receive the signal of TD from ECU) is 6,5 volts (according to 6/12v MB specs).
-- Checked all the wiring from ECU to all components, everything OK.
-- Checked all the wiring from IDLE control to all components, everything OK.
-- Changed the Throttle switch.
-- Changed all the gaskets, O-rings and vaccum pipes on the intake manifold (a few months ago, trying to discard any vaccum leak)

Any idea to fix that problem?

Thank you.

Even though the differential pressure is "close" to perfect, I would start with a slight adjustment of the EHA.

I tried that adjust, but I has to return to original adjsutment.
The problem is not the pressure, is the current. Maybe there is a faulty sensor or something, but I don't know.

It is possible for an EHA to provide proper pressure, but have something wrong with the electronic part.

My last EHA was fine, until you revved the engine off idle, and the current would slowly max out on my VOM. I replaced the EHA with another, and it gave proper current readings.

Thanks for the answer!!
At last I founded a german web where they says as you say, that my car has another problem, because the EHA current are perfect.
Searching, I founded the distributor cap with the center pin ( for the coil) interrupted, so the spark was too weak. Changed the cap, the engine runs fine again.