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W124-88 Pieburger probleme start

Hello again,
believe me to have found one reason why the car only starts and then stops. I found the choke to close when I turned the key but it opened fully at once. It should open slowly as the engine gets hot. What can keep it from being closed? If I hold the shock damper closed with my finger and open it slowly as the engine gets hot then everything is ok.
 
See
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&ved=2ahUKEwip3aLiyM7kAhWvThUIHZA1AOsQFjAKegQIABAC&url=http://www.w201club.com/forum/index.php?act=attach&type=post&id=56&usg=AOvVaw1qg7CQhgSdPy60ZVgxhw2J


The choke plate is activated by the choke actuator motor Y 22/1 In power off it should be in open position via the choke compression spring [see item 32 page 15] in the idle air compensation assembly With ignition on it should close activated by the motor driven by a signal from the carburettor control unit which will be in receipt of an engine temperature signal from a sensor- as the engine warms up it should then cause the motor to move the choke plate to the open position. This would suggest a problem with the carb control unit or engine temperature sensor -if there was a problem with the motor it should not close the choke plate on cold switch on.
STEP1 check the choke plate is open when the ignition is off
STEP 2 check the choke plate closes with ignition switch on [ engine cold]
STEP 3 check the choke plate graduaally opens as the engine warms up
1 checks the actuator mechanism/spring
2 checks the motor
3 checks the electronics
 
Last edited:
Hi,
The choke plate closes but do not open gradually. It open direct I drop the ignition key.
 
If it opens when you switch off the ignition then the mechanism and spring are ok. If it closes on ignition switch on [ engine cold] the motor is operating ----- Failure to open as the engine warms up points to an carburettor control electronics problem or its receiving false signals.
 
Maybe you don't really understand what I'm saying. The choke closes fully when the engine is started but it opens fully immediately when the engine starts even when the engine is cold. It does not open gradually. The engine stops. New start same behavior. After 5-6 starts, the engine has become warm and then the engine runs fine. As I understand it is something about the control of the choke that is the problem, but where?
 
If I understand you correctly
Ignition off =choke open
ignition on= choke closed---then open? [ what time period elapses?]
at what point does it open- on engine start or does it just open then close without any other event.
MERCEDES don't reveal the internal circuits of the control unit K45 so often substitution is the best way test its faulty.
K45 is supplied by the K1/1 OVERVOLTAGE PROTECTION RELAY have you tested that? Otherwise perhaps the K45 is working OK but is getting a faulty signal from one of its sensors causing it to drive the choke open?both K45 and OVP appear to be located behind the battery [ possibly behind a plastic cover]

ps post up your VIN [ chassis] number
 
Ignition off =choke open
ignition on= choke closed---then open? [ what time period elapses?] = the choke immediately opens the engine starts. When the engine stops the choke is open. When ignition on again the choke close but immediately open.
I have replaced the relay and replaced the control unit with new ones. Same result.
Maby I have to mont a separate manuel choke wire or I have to replace the Y 22 and Y21.
I have searched for used carb but no luck.
I stick my head in the wall for my knowledge is not enough and I have asked old reputed Mercedes workshops but they can give no tips.
I am extremely grateful for your good advice and attempts to help but now it is probably a stop. It gets too expensive.
Regards from North of Sweden
Eilert
 
Hi again, less to disturb but I found a post you wrote on March 15,2015 and tips a Russsian document that would be good. Do you have it saved? I can not find it. Redirect Notice

The probleme is the choke. I can´t find which component holds the choke and release it as the engine gets hot, The Y22 close the choke but what holds the choke closed?
 
If you really are stumped - then perhaps your idea of connecting the choke to a cable and control lever making it manually operated is the best idea. It is what I would do.
Is there any possibility of fitting a simpler carb from another 4 cyl Mercedes of the period? My W123 200 had a CV carb and no electrics (IIRC) and once the very worn needle was replaced it was no bother at all.
 
I do not have the knowledge if you can replace carburetors because this model has a control box that affects fuel consumption etc. It may not be possible to mount a mechanical carburetor.
Maby I have to connect the choke to a cable. But I hate to fail. Have had and repaired all my cars for 60 years so it feels heavy not to succeed with this car.
 
SOME PICTURES OF THE CHOKE MOTOR FROM THE PIERBURG MANUAL FIRST IS ON RESISTANCE TESTS
SECOND DETAILS REMOVAL OF THE MOTOR AND ACTIVATING ROD 3
THIRD CIRCUIT DIAGRAM FOR W124 AUTO TRANSMISSION [ ONLY DIFFERENCE TO MANUAL GEARBOX IS N15 KICKDOWN RELAY FOR AUTOBOX]

YYKnqnR.jpg

ucj3DK6.jpg

kr9DGa9.jpg


I would suggest the following test--- go thro the cold start proceedure observing the action of the choke plate at every stage ---resting/ignition on/start/run - repeat with the choke motor disconnected electrically then- after careful marking of position remove the motor disconnect from choke plate actuator arm and reconnect motor electrically and observe the motor movement again while in disconnected state THIS WOULD CONFIRM ERROR MOTOR SIGNALS
 
Hi again, The problem is finally solved with difficult to start car. I have no recollection that I had loosened the potentiometer R24 but apparently I had it loose when I cleaned the carburetor and then the little plastic sleeve was dropped off and ended up on the floor. The problem with the car was that it did not start cold because the choke closed but immediately opened. There the problem was that no one could answer what kept the choke in the closed position to slowly open as the engine became hot. By chance, I discovered a round piece of plastic on the garage floor. I brought it up and remembered that I had seen something similar in an instruction that I had been advised about. Said and done. I removed the carburetor and removed the potentiometer R24 and discovered that the plastic bit was gone. Mounted it and installed the carburetor and started. The choke closed and was kept in the closed position. Slowly opened as the engine warmed. All clear. Problem solved. A huge thank you to you who have been helpful with various tips and advice. The car now runs as it did before. I am very happy. The mistake I made was to buy a used OVP relay. Would have bought a new one then the problem would have been solved very early and to a cheaper final note.
Once again, thanks for help. Probleme solved.
 

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Right -- problem solved --congratulations. Like many strange problems they often stem from assumptions that certain things are normal when they are not. That missing bit of plastic - a short cylinder with slots at either end acts as a coupling between the primary choke throttle plate and its position potentiometer. With it missing the carburettor control electronics had no way of knowing the throttle plate angle in the primary choke and I assume went into some sort of fuel cutoff mode which involved opening the choke plate also located in the carb primary choke. So the choke itself was operating correctly according to the signals it was getting after all.
Thanks for posting the solution [ and pictures] to the problem
 
Finding the plastic piece was incredible. It has been on the floor for over a month. I have vacuumed, washed the floor several times and it has stayed. An incredible turn to find it.

Once again, many thanks.
Eilert from the North of Sweden.
 
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