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Air Flow Meter Problems
Topic Started: Mon Dec 22, 2014 5:44 am (621 Views)
Doug11
Newbie
[ * ]
Sorry, I think I originally posted this in the wrong section.

I have gone from a sweet running 190E with a minor cold flatspot, do one that is difficult to start and runs rough for 15 seconds


I knocked the pin down of the AFM to get the air flow sensor plate aligned as per all of the instructions (it was sitting about 3mm higher than the center of the venturi) and now have no freeplay between the basic and rest positions (was 1 to 2 mm before).
Car now is difficult to start and idles rough for 30 seconds.
Any bosch experts out there ?

I tried adjusting the mixture to get the freeplay back, but that involved 2 whole turns of the mixture screw, and of course the car wouldn't run when the mixture was that bad.

I think I need to taste the fuel distributor off and tap the AFM pin back up to where it originally was.


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Deleted User
Deleted User

Have you reset the fuel/air mixture adjustment with a dwell meter?
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Doug11
Newbie
[ * ]
Thanks Charles.
Yes, got it to close to 50 % at both warm idle and 2500 RPM.
It take 2 full turns clockwise of the 3mm mixture adjustment before the AFM basically releases from the basic position and it can flap up about 1mm as it it should. Problem is that then the mixture is so far put the car wont idle.
This is 2 full turns away from the 50% duty cycle setting.
I think i will take it off and tap the pin back up, for some reason the rest position must be about 3 or 4mm above what all of the manual say, which is strange.
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eagle3
Therapy Needed
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Maybe you're barking up the wrong tree and the fault lies elsewhere. There are a few possibilities.

Edited by eagle3, Mon Dec 22, 2014 9:11 am.
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Doug11
Newbie
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Yes, thats what i thought too. But i am reasonably handy around the M102, having rebuilt a couple of top ends and replaced fuel injectors, adjust mixture etc.
I just cant seem to work out what is going on. Car runs fine after about 30 seconds and after 10 erratic seconds starting.
Up until i tapped down the AFM height pin it started instantly hot or cold into a smooth idle and ran perfectly except for a minor flat spot when cold.
Temperature sensors all check out to spec.
Any thing else to check would be appreciated, i just cant work out why setting the AFM height to spec. Has suddenly created all of these problems.
The car is mint and still had the plug in the mixture adjustment hole.
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Gaz2N
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Old Merc nutter
[ *  *  * ]
Doug11
Mon Dec 22, 2014 12:16 pm
Yes, thats what i thought too. But i am reasonably handy around the M102, having rebuilt a couple of top ends and replaced fuel injectors, adjust mixture etc.
I just cant seem to work out what is going on. Car runs fine after about 30 seconds and after 10 erratic seconds starting.
Up until i tapped down the AFM height pin it started instantly hot or cold into a smooth idle and ran perfectly except for a minor flat spot when cold.
Temperature sensors all check out to spec.
Any thing else to check would be appreciated, i just cant work out why setting the AFM height to spec. Has suddenly created all of these problems.
The car is mint and still had the plug in the mixture adjustment hole.
Have you read this months MB Gazette?

There is an article in there that may be of help.

Gary
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Doug11
Newbie
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Hi Gary,
No i dont get the Gazette.
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Gaz2N
Member Avatar
Old Merc nutter
[ *  *  * ]
Doug11
Mon Dec 22, 2014 9:54 pm
Hi Gary,
No i dont get the Gazette.
I would recommend that you join. The parts saving alone at the dealer usually pays for the annual subscription.

You will need to check the boot under the AFM unless you've replaced it, it's likely to be letting in un-metered air.

Once you are sure that's ok you'll need to check all the sensors and switches one by one. Again there are plenty of resources on the Mercedes Benz Club website to assist.

Hope that helps

Gary
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ConorD
Claiming Newbie status still
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Gaz2N
Mon Dec 22, 2014 11:14 pm
Doug11
Mon Dec 22, 2014 9:54 pm
Hi Gary,
No i dont get the Gazette.
I would recommend that you join.
Gary
+1
It's a great club, and rarely do a couple of months go by without an article in the Gazette with some info on the 190!

Also, they have Model Register Captains for various models including the 190 who really know their stuff, as do many of the online contributors there. It's not as active as this forum but still worth a regular visit.

ConorD
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Deleted User
Deleted User

worst case, I suppose you could buy a new one, and use the old one for parts.
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