rorf
Active Member
Grober certainly knows his stuff
grober
MB Master
The EHA was introduced to fine tune the mixture via the engine ECU with the introduction of catalytic converters and lambda sensors. It sounds as if its functioning correctly but receiving the wrong signals from the ECU possibly because the ECU is getting false signals from the sensors.
This PDF details how to check the correct functioning of these sensors.
http://www.w124performance.com/service/w124CD1/Program/Engine/103/07.3-0121.pdf
and how to check the full throttle/idle switch
http://www.w124performance.com/service/w124CD1/Program/Engine/103/07.3-1689.pdf
This PDF details how to check the correct functioning of these sensors.
http://www.w124performance.com/service/w124CD1/Program/Engine/103/07.3-0121.pdf
and how to check the full throttle/idle switch
http://www.w124performance.com/service/w124CD1/Program/Engine/103/07.3-1689.pdf
ray_hennig
MB Enthusiast
i swapped the ke unit for an exact part i had from a previous salloon car i had, just to see if previous owner had damaged it from jumping, start car , 85 degrees dead,
ok, so then on to Graemes trick of DISCONNECTINGthe EHA, obviously i had to wait for the car to go cold
start car, disconnect EHA, 85 degrees AND STILL RUNNING, dare i say it but it idles better with the EHA disconnected , it is much smoother when revved then back to idle,
do i need to have this connected?
So, no EHA = no cut-out at 85C? Interesting. In a KE system, the EHA is a significant refinement so it should be connected.
Have I read this right? You cannot suspect the EHA because you've tried two different examples. Is that true? In any event, I cannot imagine the EHA causing an immediate cut-out anyway.
Or did you use the same EHA when you "swapped the ke unit"?
Do keep us posted with your progress as I have hot running issues (no cut-out) and I know the EHA is a potential source of grief.
I await with interest.
RayH
This is what i done, firstly i was worried when it was mentioned that the unit could have been damaged during a jump start (KE UNIT)
so first thing this morning i tried another ke unit that i was lucky enough to have.
the symptoms were the same, so i could rule out the ke unit.
so i then tried the tip recommended by Graeme, and disconnected the eha, and all is well, car starts and runs as long as you like (it actually runs smoother), as the ke unit is alright and it has new coolant sensors, and the eha is actually working, it must be the throttle micro switch as mentioned earlier, which i will source this week, at the moment the car is running fine without the eha,
so in short.....same eha unit while i swapped ke unit
so first thing this morning i tried another ke unit that i was lucky enough to have.
the symptoms were the same, so i could rule out the ke unit.
so i then tried the tip recommended by Graeme, and disconnected the eha, and all is well, car starts and runs as long as you like (it actually runs smoother), as the ke unit is alright and it has new coolant sensors, and the eha is actually working, it must be the throttle micro switch as mentioned earlier, which i will source this week, at the moment the car is running fine without the eha,
so in short.....same eha unit while i swapped ke unit
Last edited:
It could still be dry joints in the OVP opening up as it gets up to temp. They do get hot. It's what causes the solder to dry and crack after so many heat cycles.
Every thing electrical on the KE and ABS systems run through this relay. You need to open it up and check the solder joints with a Jewelers Loupe or strong magnifying glass. I have watched so many people try this and that, replace part after part, until finally fixing or replacing the OVP, to suddenly find all is working just as it should again.
Another thing to check are the connectors and wires to the temp sender at the right rear of the engine. Broken wires can and will send duff signals to the ECU. 3 out of the 5 mercs I have owned from this era have either had them replaced before I bought the car, or I have had to replace the connectors myself. They are cheap from MB and come with a good length of wire attaches so that you can trace back any breaks then cut oand solder in the new wires and connectors.
Every thing electrical on the KE and ABS systems run through this relay. You need to open it up and check the solder joints with a Jewelers Loupe or strong magnifying glass. I have watched so many people try this and that, replace part after part, until finally fixing or replacing the OVP, to suddenly find all is working just as it should again.
Another thing to check are the connectors and wires to the temp sender at the right rear of the engine. Broken wires can and will send duff signals to the ECU. 3 out of the 5 mercs I have owned from this era have either had them replaced before I bought the car, or I have had to replace the connectors myself. They are cheap from MB and come with a good length of wire attaches so that you can trace back any breaks then cut oand solder in the new wires and connectors.
ray_hennig
MB Enthusiast
I hope nobody minds me rattling on about this problem here, but its driving me nuts!, today has been my first chance to work on the car.
I have checked the micro switch on the throttle linkage, as this was said to be the most likely cause, with a meter it opens and closes, then i put the wiring plug on and checked and the wiring is good.
I then checked the wire from the switch to the ovp relay, to make sure it was being fed and that is ok.
I have removed the ovp relay and checked thoroughly with a meter and a loupe! and it is ok
So the ke unit is good
the switch on the throttle is good
the temperature sender is new
the ovp is good
and the EHA works
Graeme was kind enough to link me to info on checking everything, can anybody tell me where to start now.
OR can i just run the car without the EHA connected, as i said before it runs fine without it, if anything its better
I have checked the micro switch on the throttle linkage, as this was said to be the most likely cause, with a meter it opens and closes, then i put the wiring plug on and checked and the wiring is good.
I then checked the wire from the switch to the ovp relay, to make sure it was being fed and that is ok.
I have removed the ovp relay and checked thoroughly with a meter and a loupe! and it is ok
So the ke unit is good
the switch on the throttle is good
the temperature sender is new
the ovp is good
and the EHA works
Graeme was kind enough to link me to info on checking everything, can anybody tell me where to start now.
OR can i just run the car without the EHA connected, as i said before it runs fine without it, if anything its better
I hope nobody minds me rattling on about this problem here, but its driving me nuts!, today has been my first chance to work on the car.
I have checked the micro switch on the throttle linkage, as this was said to be the most likely cause, with a meter it opens and closes, then i put the wiring plug on and checked and the wiring is good.
I then checked the wire from the switch to the ovp relay, to make sure it was being fed and that is ok.
I have removed the ovp relay and checked thoroughly with a meter and a loupe! and it is ok
So the ke unit is good
the switch on the throttle is good
the temperature sender is new
the ovp is good
and the EHA works
Graeme was kind enough to link me to info on checking everything, can anybody tell me where to start now.
OR can i just run the car without the EHA connected, as i said before it runs fine without it, if anything its better
I have checked the micro switch on the throttle linkage, as this was said to be the most likely cause, with a meter it opens and closes, then i put the wiring plug on and checked and the wiring is good.
I then checked the wire from the switch to the ovp relay, to make sure it was being fed and that is ok.
I have removed the ovp relay and checked thoroughly with a meter and a loupe! and it is ok
So the ke unit is good
the switch on the throttle is good
the temperature sender is new
the ovp is good
and the EHA works
Graeme was kind enough to link me to info on checking everything, can anybody tell me where to start now.
OR can i just run the car without the EHA connected, as i said before it runs fine without it, if anything its better
Thought i would add this footnote, as it may help somebody in the future.
First my thanks to Graeme for nursing me through this problem.
The culprit was indeed the throttle position switch / sensor as mentioned early on in this thread.
A new sensor fitted today and all is well......fiddly job but removing the idle control valve makes it easier.....thanks to all who helped (I could not run old mercs without the help of you guys)
First my thanks to Graeme for nursing me through this problem.
The culprit was indeed the throttle position switch / sensor as mentioned early on in this thread.
A new sensor fitted today and all is well......fiddly job but removing the idle control valve makes it easier.....thanks to all who helped (I could not run old mercs without the help of you guys)
kth286
MB Enthusiast
What do feel was the matter with it, as I thought you tested it to be OK initially ?
I had a meter on the unit and the voltage swept from about 0.5volts to 4.5volts without any spikes, this is not the way to test though, as Graeme pointed out to me.
at closed throttle there should be resistance between pins 1 and 2 (closed switch), the old unit did not do this, I had assumed if it had voltage and moving with the throttle it was ok
