Airflow Sensor Plate Position:

[mmansilla]

Hello group, I'm new.
I was wondering if someone here knows the proper height position of the air sensor plate on a 124, 92 230E.

The airflow cone has this three sections (see drawing please):
1. Inverted cone, exterior
2. Flat portion
3. Interior Cone

On the other hand, while resting, engine off, the plate has a travel free of resistance, between what I believe are called the 'zero position' and the 'basic position'. One feel resistance while pressing down with fingers when the 'basic position' is reached.

What I need to know is if the rest positions showed with the red lines on the attached drawing are correct, meaning:
- zero position: top edge of the plate even with the end of the inverted cone
- rest position: bottom edge of the plate even with the beginning of the interior cone.

Also, how this two heights can be modified?

Thanks in advance for any help.
MMansilla

[Mike Murrell]

I don't have anything specific for the qustion you have presented, but I have found Steve Brotherton's comments in this thread to be interesting. There is a relationship:

89 560 SEC Died in a parking lot Please H E L P !

[sbourg]

While it's not my position to ask why you want to know, I'll point out that the adjustment should only need to be considered if the airflow meter or fuel distributor have been replaced. It is unlikely to need adjustment as a maintenance item. The most common maintenance or repair issues with the airflow meter are cleaning the throat and plate, usually done without removing it, and replacing the potentiometer mounted on the pivot axis, also done without removing the unit. This latter would be likely indicated if your idle is erratic, speeding up then slowing down to normal, sometimes with an off-idle stumble too.

Note too that the entire airflow meter and fuel distributor can be removed and reinstalled as a unit, requiring no subsequent calibration, if a really thorough cleaning is indicated.

Steve

[mmansilla]

Thanks for the responses.
Well, now that you mention it, I agree. Chances of a well positioned plate are greater than of the opposite. However, I have been trying to improve the vibrating idle of this car (90k miles) during the last months. So far I have replaced filters (all), injectors/seals, engine and transmission mounts, broken idle air hoses, O2 sensor, spark plug wires, dist cap and rotor, and fixed vacuum leaks. With all this the idle improved, let's say 60% (engine startings, fuel economy and power too).

After studying CIS KE Jetronic, the sensor plate caught my attention and saw that the lateral position was displaced to one side of the cone walls. It was just a tiny deviation, but after I centered it with the central screw the idle improved, a lot.

Now the car is idling, let's say 90% well, and I realize that the engine behaviour is very sensitive to the plate position. Idle is smooth now, but it has yet this periodic small pulsation, so I wanted to be sure that the rest height of the plate is right.

Thank you, very much.
MMansilla

[bpaz_ph]

Just for future reference, how do you take off the potentiometer without breaking the plastic cover?

[mmansilla]

I'm not sure what do you mean Bpaz, I didnīt remove the potentiometer. The potentiometer is a small black box at one side of the fuel distributor which 'tells' the ECU the position of the sensor plate. I worked on the plate itself.

I can tell you, for reference, that I used a feeler gauge, as the one showed in the picture, to CENTER the plate in the throat. I lossen a bit the central screw of the plate and slid the 0.05 mm blade of the feeler between the plate and the throat. When the perimetral gap was even I tightened the screw.

Easy. However if you donīt have any significant idle or starting problem, I suggest to leave the plate alone. Its movement is linked to a small piston inside the chambers of the fuel distributor which, along with the ECU via the EHA, determines the delivery of fuel, so the injection system is very, very sensitive to its position.

MMansilla

[bpaz_ph]

Sorry, I was referring to sbourg's comment on replacing the potentiometer.

I just recently went through and solved my duty cycle problems and while reading it was mentioned that the potentiometer wears with age especially at the idling portion.

Considering our car's age it would be nice to know how.

[mmansilla]

Oh, I see.
It wears at the idle portion...Interesting, I will test its resistance.
Thank you

[bpaz_ph]

Yep.

Some peolple even mentioned cleaning it but I didn't find any info on how to take it off. The plastic cover fits in tight I'm afraid it might break if I try to pry if off.

There was some mention of replacing the whole air flow assembly but that option is too $$$.

[mmansilla]

I'm curious about your cleaning idea Bpaz.
There is 4 screws on the plastic cover of the potentiometer. Even with the screws removed, is it hard to take off the plastic cover to get to the area for cleaning? Is there something else hard to remove, behind the plastic cover?
Thanks

[sbourg]

The plastic cover IS part of the pot. Screws loosened, the pot can be rotated, so scribe an alignment mark before this step. It should slip straight out off the pivot shaft of the airflow meter, while the wiper stays captive to the shaft. Find previous posts to see pics of what the pot looks like.

Cleaning the pot is unlikely to be successful, but a worn pot displays definite symptoms. Idle speed varying erratically is typical. A rough idle with minimally varying idle speed is not a symptom.

Resistance measurements are useless, as this pot is used as a voltage divider. It incorporates a large resistance in series with the wiper. A valid test would involve a test harness to apply a voltage across the outer terminals while monitoring the voltage at the center pin. It would be done with the pot mounted, engine off, and manually actuating the airflow meter plate. Simpler is to go by symptom and visual inspection.

Steve

[sbourg]

Originally Posted by mmansilla

After studying CIS KE Jetronic, the sensor plate caught my attention and saw that the lateral position was displaced to one side of the cone walls. It was just a tiny deviation, but after I centered it with the central screw the idle improved, a lot.

I would suspect if you removed the airflow meter, you would find wear at the pivot bearing surface to cause the lateral displacement. If your solution works, that would certainly save replacing a very expensive part. It is safe to say the plate should not rub anywhere the venturi sides, and centered laterally would be the design spec.

Steve

[bpaz_ph]

Beautiful info.

Thanks

[mmansilla]

It worked Steve, at least for now. I had to center the plate three times though, because it kept getting off center after short rides. A wearing on the pivot could be the phantom that moves the plate (hope not).
Fortunately, it has remained perfectly centered for a week now, after I used a locking compound on the central screw thread. The idle becomes smoother, almost silky, but for this little pulse every five or ten seconds, mostly notorious when the engine is reaching normal operating T°.
You describe a much more rough idle in case of a worn potentiometer, and given my lack of experience, I donīt think is worth (yet) to dismount the pot. My obsession with the idle goes now towards learn how to measure and regulate the KE duty cycle (thanks Bpaz). I recently replaced the O2 sensor, and according to what I've read in this great forum, it's good to do it.
Thank you, I really appreciate your advice and thoughtful responses.

[Chiappino]

After using this thread for research......(Thank you very much). I think I have found my problem. However I cannot find the solution.

My car (1984 Euro 500SL) had been sitting for years. I heard a lot about clearning the airflow plate if it was sticky. I pushed down on it with the car off, it had medium pressure. But as it wouldn't go any further, the plate popped right back up to it's usual position, and now it is extremely easy to push down. Flicking my finger on it would allow it to travel it's entire distance.

ALSO, I believe I'm flooding the hell out of my engine now!!! I have fuel dripping from somewhere where there never was before. My car will turn over for days, but won't come close to firing. Please help!!!!!

Thank you

Chase
1984 Euro 500SL