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1996 E300D
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84 Posts
Discussion Starter #1
The OM606NA engines in the 1995-1997 E300 have a vacuum-operated flap just ahead of the EGR valve. FSM calls it the "pressure control flap" and says it's part of the EGR system. (This is NOT one of the two "resonance" flaps.) In its position ahead of everything but the air filter, the flap acts as a throttle (which diesels usually don't have) and reduces air pressure in the intake manifold. The only purpose of the lowered pressure would seem to be that it allows more exhaust in through the EGR valve when it is open. Since the EGR valve of my '95 E300 has been temporarily disconnected for testing purposes only, there isn't a need for the pressure control flap, so I have removed it. So far there seem to be no effects, for good or for ill. Has anyone else played with this flap? What were your results? What do you think its purpose is?

Note: In the '96-97 E300 (W210) there is an added pressure sensor that looks at the intake manifold and expects to see a pressure drop when the flap closes. If it doesn't see the drop it sets a flag. Therefore, flap removal in these two later versions is more challenging.

Jeremy





 

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Cruise Control
'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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52,233 Posts
The '90 - '93 OM602 engines also have these flaps. I believe its sole purpose is to serve the EGR functions. I removed mine at my earliest convenience. I replaced the entire housing with an 8" section of 2.25" silicone tubing

 

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Registered
1996 E300D
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84 Posts
Discussion Starter #3
Clever fix, thanks. The OM603 engines, at least the early ones in the 1987 300D, don't have this flap. Wonder whether the later 603.97 "rod bender" in the S-class cars got it?

A friend told me the few cars of this model (the '95) in Australia are completely missing the EGR valve and throttle flap; they have a plain aluminum section in its place. Your OM602 might have been similarly treated.

Jeremy
 

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Cruise Control
'87 300TD/'90 300D/'94 Quattro/'89 Vanagon TDI/'01 EV Weekender VR6
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52,233 Posts
The '87 190D 2.5T (OM602) was also sold without the mixer flap. MB sure used to make an awful lot of variations on a theme.
 
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