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  #1  
Old 04-06-2006, 03:32 PM
Fixin' anything moving
 
Join Date: Sep 2004
Location: Fort Worth, TX
Posts: 247
CIS injection question

Dear All,

(this is regarding my 1983 380SEC).
Should the air flow sensor (the big circular plate) be completely closed when the engine is idling?
I.e., is the idle control air flow valve able to supply all the air that is needed by the engine to idle?
If it is supposed to be closed, then the control piston in the fuel distributer rests at its bottom position (as the control pressure exceeds that of the air control valve's), right?

Your input is greatly apreciated.

Greg

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1983 560SL Megasquirted (originally 380SL)

My former Mercedes:
1985 300SD ~190k
1990 560SEL
2000 C220 CDI
1983 380SEC 102k dual-chain conversion
2000 C280 70k (sold)
1987 300DT (W124 - sold)
1972 220D (sold)
1971 220D (sold)
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  #2  
Old 04-06-2006, 03:39 PM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
All the air that passes into the motor passes though that plate. The plate DOES NOT regulate airflow it measures airflow. The idle valve bypasses the throttle which is below the airflow plate but it gets its air through the plate. If this was not so then the distributer would not know how much fuel to add.

Remember engine speed is determined by controlling air not fuel. Fuel is just matched to quantity of air. Wrong amount of fuel either too much or too little causes the engine speed to drop.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #3  
Old 04-06-2006, 03:50 PM
Fixin' anything moving
 
Join Date: Sep 2004
Location: Fort Worth, TX
Posts: 247
So bottom line is: even at idle the air flow valve should be slightly open, right? (what is sligtly? - a couple of mm?)
__________________
1983 560SL Megasquirted (originally 380SL)

My former Mercedes:
1985 300SD ~190k
1990 560SEL
2000 C220 CDI
1983 380SEC 102k dual-chain conversion
2000 C280 70k (sold)
1987 300DT (W124 - sold)
1972 220D (sold)
1971 220D (sold)
Reply With Quote
  #4  
Old 04-06-2006, 05:27 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The way to gauge it is not with the engine running but with the engine off. The plate should be at the bottom of the portion of the airflow cone that has verticle sides. There is a small length of the cone that is machined flat. As the plate leaves this area the gap grows quickly. It should be in the area of continuos gap, but just about to leave it. Once the motor is running the plate drops into the area of significant gap and the amount depends on engine speed and mixture adjustment.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #5  
Old 04-06-2006, 05:40 PM
Fixin' anything moving
 
Join Date: Sep 2004
Location: Fort Worth, TX
Posts: 247
I am sorry Steve, I am confused now:

Are you saying that if the engine is off, then the plate is not (should not be) all the way closed?
If I remember correctly as I have removed the fuel distributor, the valve was in the closed position and when I moved it, it returned to a closed position...
__________________
1983 560SL Megasquirted (originally 380SL)

My former Mercedes:
1985 300SD ~190k
1990 560SEL
2000 C220 CDI
1983 380SEC 102k dual-chain conversion
2000 C280 70k (sold)
1987 300DT (W124 - sold)
1972 220D (sold)
1971 220D (sold)
Reply With Quote
  #6  
Old 04-06-2006, 06:31 PM
Moderator
 
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The problem is with the definition of closed. If closed is the off position then of course it should be in the closed position when off. The point is there is no "closed" position. The plate can pass all the way through the narrow point of the funnel. There is a narrow point in the middle, the funnel gets wide above and below that point. The proper place at rest is in the narrow position. The best at rest position is to be where the bottom edge of the plate is even with the exact edge of the narrow position. The narrow position is wider than the thickness of the plate. Again. the good place to be is for the bottom surface of the plate to be even with the exact edge of the narrow section. This is a distinct crisp line, just as the top edge of the narrow section is a distinct crisp line.

Its not that critical though, anywhere within the narrow section is fine.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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