CIS air flow potentiometer possible fix?

[Stretch]

G'day Folks,

I'm not sure (but after a replace everything else process of elimination the chance seems to be pretty big) if my air flow sensor potentiometer is causing the uneven idle problems on my M102 or not because I haven't taken the one off of my car just yet...

...But I have "practiced" on some spare parts I bought and I can see on the spare part that there are wear marks in the sensor =>



{ For the record and future searching this is about the following parts
Car Part BOSCH 3437224035, Elements of injection of fuel (3437224035)

Car Part BOSCH 3 437 010 039 (3437010039), Repair Kit, distributor (3437010039)

Car Part BOSCH F 026 T03 021 (F026T03021), Adjusting Potentiometer, idle mixture (F 026 T03 021)

And possibly this MB number 3437224015

These numbers seem to come up in combination with each other - please check for yourself before you use them to buy anything!!!}



Anyway the sensor has skid marks on it where the lever at the end of the "throttle plate" in the CIS air control gubbins have been rubbing up against it...

...I was thinking =>

RE-COAT - repair the surface.

Clear high temperature paint is often used in alternators and starter motors to isolate windings from other parts of the the machinery.

I guess varnish would do the same.

I have the sudden urge to try to repair the surface of this spare part with a bit of yacht varnish.

However before I do that perhaps someone here (perhaps an electrickery genius?) has a better idea?

[Elektri]

I would replace it. Actually I did replace it on my car - that is a wear item which needs replacement every so often.

I can't imagine anyone could "fix it" and it have a consistent resistance range just like a new part.

[Stretch]

Originally Posted by Elektri

I would replace it. Actually I did replace it on my car - that is a wear item which needs replacement every so often.

I can't imagine anyone could "fix it" and it have a consistent resistance range just like a new part.

Thanks for the reply.

I have got a new one on order - I was just wondering if either of my old ones could be saved.

I'm planning to give it a go with ye olde yacht varnish - if it doesn't come good then there's just a bit of varnish and some of my time wasted...

...but think of the pay off if this does work!

[Frank Reiner]

Originally Posted by Stretch

G'day Folks,

Anyway the sensor has skid marks on it where the lever at the end of the "throttle plate" in the CIS air control gubbins have been rubbing up against it...

...I was thinking =>

RE-COAT - repair the surface.

Clear high temperature paint is often used in alternators and starter motors to isolate windings from other parts of the the machinery.

I guess varnish would do the same.

I have the sudden urge to try to repair the surface of this spare part with a bit of yacht varnish.

However before I do that perhaps someone here (perhaps an electrickery genius?) has a better idea?

Is not the "rubbing up against it" action one of making contact with a resistance? When the wiper is moved along the resistor, the resistance value changes with the position of the wiper.
If an insulating material (varnish or the like) is applied to the contact surface, there will no longer be contact and conductivity between the wiper and the resistor.

[97 SL320]

The black areas are conductive and is what gives the sensor variable resistance so insulating paint won't work.

A paint kit that repairs heated rear windows is a possibility however we don't know the resistance per area of the old and new paint.

Have a look at the center terminal, go to the right and down a slight bit. You will see a thin white line. Look further to the right and you will see more lines. These are laser cut lines to adjust the sensor linearity and calibration.

[Stretch]

Originally Posted by Frank Reiner

Is not the "rubbing up against it" action one of making contact with a resistance? When the wiper is moved along the resistor, the resistance value changes with the position of the wiper.
If an insulating material (varnish or the like) is applied to the contact surface, there will no longer be contact and conductivity between the wiper and the resistor.

Originally Posted by 97 SL320

The black areas are conductive and is what gives the sensor variable resistance so insulating paint won't work.

A paint kit that repairs heated rear windows is a possibility however we don't know the resistance per area of the old and new paint.

Have a look at the center terminal, go to the right and down a slight bit. You will see a thin white line. Look further to the right and you will see more lines. These are laser cut lines to adjust the sensor linearity and calibration.

Oh bugger I thought it was a proximity sensor - some sort of Hall effect thing perhaps - well something that didn't rely on conductivity.

OK varnish isn't going to work.

[97 SL320]

And just for completeness. Hall effect ( transistor ) uses magnetism to trigger. Any sort of physical contact is avoided as actual contact isn't needed or desired.

[Stretch]

I've been reliably informed that there is such a thing as carbon track repair paint but at the same time been told not to bother!

This is a bit of a shame. All I can say it thank goodness for ebay knock offs as the price of the original part is seriously expensive.

[Stretch]

Here are some pictures of the replacement part I bought.

Apparently it comes from the same factory that makes them for Bosch (so the advert says). Does have all the numbers stamped / in the casting...





Paid less than 40 euros delivered (packet post costs about 7 euros)

[rayhennig]

Originally Posted by Stretch

Here are some pictures of the replacement part I bought.

Apparently it comes from the same factory that makes them for Bosch (so the advert says). Does have all the numbers stamped / in the casting...





Paid less than 40 euros delivered (packet post costs about 7 euros)

Is that the one that's advertised in Germany as the (I think) "Black Edition"?

I ask because I was thinking of trying one myself. Someone somewhere suggested that this Black Edition was more expensive (45€?) than the ordinary version because it was selected from a Chinese factory batch, tested and warranted as working to spec. No idea if it's true.

Do let us know if it works.

Bonne chance.

RayH

[Stretch]

Originally Posted by rayhennig

Is that the one that's advertised in Germany as the (I think) "Black Edition"?

I ask because I was thinking of trying one myself. Someone somewhere suggested that this Black Edition was more expensive (45€?) than the ordinary version because it was selected from a Chinese factory batch, tested and warranted as working to spec. No idea if it's true.

Do let us know if it works.

Bonne chance.

RayH

"Black Edition" => that sounds a bit "jizz and whizz" for me!

The guy I bought it from says in his advert that the sensors come from the same factory where Bosch gets them. I get the impression if they were extra special the guy would have used that as a selling point.

I fitted it today. I have a few more things to fiddle with and then I'll be able to say for sure if this has fixed the uneven idle or not.

[97 SL320]

The part looks like it will operate but I don't see any laser trimming of the calibration resistors. This can cause a linearity problem. ( some plate positions may read higher or lower than desired.

The top of the resistor track near the solder joint looks to have some white like it is covered with flux, this could affect operation at high throttle.

[Stretch]

Not a difficult job to do but the sodding thing does not give an especially steady output. But then neither did the old ones.



The range for the output is 0.7 volts +/- 0.1 volts

This is a very fortunate picture!



The reading can vary by as much as +/- 0.1 volts

I think if the multimeter had a steadier frequency response it would seem to be a bit less of a fuss pot.

(Notice what I did there?)

This fix doesn't look like it has fixed the lumpy idle completely - I need to drive the car for a bit to make sure, but I get the impression it may (just may) have helped a little bit.

[Marcel107]

When I see the solderjoints on the black one, I think it is junk and not a quality Item.

The colored one on the Top looks much better.
Regards from Germany
Marcel

[optimusprime]

Could you clean your air control valve.I use carburetor and injection spray . . And check all earth points , clean them up and put a little grease on them as you refit.Also check the vacuum pipes for holes .