Re: [MBZ] Mercedes Digest, Vol 2, Issue 190

[Dave M.]

Good point, Andrew. Also remember than any restriction in line with
the ALDA will reduce part-throttle power, as the ALDA will get a
delayed signal from the charge pipe. This was the fix Mercedes
foisted upon the 1986/1987 models to correct a lean surge with the
cruise control. It's shown in the FSM complete with restriction
orifice, an extra switchover valve, and a bunch more plumbing. With
the EGR/ARV disconnected and ALDA adjusted it's not needed - I removed
it from my cars. I think you would need more than 1-2 inches of vacuum
before it would actually affect fuel delivery but I'm not sure about
that.

=)

-Dave M.

 --
 Date: Sat, 30 Jul 2005 08:05:20 -0400
 From: Andrew Cunningham [EMAIL PROTECTED]
 Subject: Re: [MBZ] Boost line check valve?
 
 Casey,
 
 I have been playing with the signal to the ALDA with the 617 engine,
 not yours though.  If there is a check valve (at least on the 617) the
 ALDA will stay pressurized from your peak boost even after you take
 your foot off the go pedal.  Until it leaks down to the correct intake
 pressure your IP will be spitting out more fuel at a given throttle
 position than it should be.  Perhaps, Marshall can weigh in and
 confirm.
 
 Out of curiosity, how much is a fair amount of vacuum?
 
 Andy
 
 
 On 7/29/05, Zeitgeist [EMAIL PROTECTED] wrote:
  The latest thread about leaky valve stem seals has gotten me to think
  about the presence of pressure and (a little) vacuum in the intake
  manifold.  I've been monitoring my boost pressure gauge and have
  detected a fair amount of vacuum in the intake off idle until boost
  builds.  I'm also experiencing a bit of throttle lag off idle, before
  the beast leaps forward with a vengeance, so I'd like to put a
  pressure check valve in the line between the manifold and ALDA, so I
  can test a theory
  (btw: I know about adjusting the ALDA screw or shimming, so hold that
  thought).
 
  Does anyone know of small orifice check valve for either pressure or
  vacuum (I assume these can just be turned around, right?)?  Does MB or
  another make use one of these check valves?  I've seen vacuum filters
  and reducers, but not a small orifice check valve so far.
 
  TIA
  --
  Casey
  Biodiesel:
  '87 300TD intercooler (206k)

Re: [MBZ] Mercedes Digest, Vol 2, Issue 190

[Zeitgeist]

Not sure if you were CC'd Dave, but Andrew came up with a rather
elegant solution; tee in a vacuum check valve, into the boost line,
which would avoid trapping pressure in the aneroid chamber.  This
would vent manifold vacuum from a separate source, rather than the
ALDA.  Another additional option might be to source the ALDA boost
signal right at the turbo, which might help avoid boost lag due to IC
plumbing losses.

On 7/30/05, Dave M. [EMAIL PROTECTED] wrote:
 Good point, Andrew. Also remember than any restriction in line with
 the ALDA will reduce part-throttle power, as the ALDA will get a
 delayed signal from the charge pipe. This was the fix Mercedes
 foisted upon the 1986/1987 models to correct a lean surge with the
 cruise control. It's shown in the FSM complete with restriction
 orifice, an extra switchover valve, and a bunch more plumbing. With
 the EGR/ARV disconnected and ALDA adjusted it's not needed - I removed
 it from my cars. I think you would need more than 1-2 inches of vacuum
 before it would actually affect fuel delivery but I'm not sure about
 that.

Casey
Biodiesel:
'87 300TD intercooler (206k) 
'84 300D (202k)
Gashuffer:
'89 Vanagon Wolfsburg Edition (184k)
Olympia, WA