FW: Re Motronic 4.1 newbie-continued

Rich M rsrich at cwcom.net
Sat Nov 6 23:49:42 GMT 1999


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  -----Original Message-----
  From: Rich M [mailto:rsrich at cwcom.net]
  Sent: 06 November 1999 23:33
  To: diy_efi (E-mail)
  Subject: Re Motronic 4.1 newbie-continued


  ------------------------------

  Date: Fri, 05 Nov 1999 20:44:33 EST

  From: "Derek Kaznoski" <sweetpea1998 at hotmail.com>

  Subject: Motronic 4.1 newbie-continued

   >I took off the ISA and examined it. The valve

  >seemed to open and close

  >without difficulty. I went ahead and cleaned it with throttle

  >body cleaner

  >to be sure (thanks Dylan). I noticed that in the fully closed

  >position,

  >there was about a 3mm gap present, i.e., the valve is over-

  >rotated past the

  >closed position.

  That's right; in the de-energised condition, the valve returns to it's
endstop which exposes a default opening which should correspond to a
high-idle setting. This is used as a fail-safe to produce a useable (if
little high) idle speed if the ISA or it's drive fails.

  >I'm

  >planning to replace it. If anyone thinks this is a bad idea,

  >please let me

  >know. Any other input is greatly appreciated.

  Before you replace it, check for splits or leaks in the air
tubing/trunking on the engine side of the airflow meter and ISA. I have come
across a similar effect of rough idle on a LE2 sytem for just this reason:
at idle the leak represents a significant bypass round the airflow meter, so
allowing the flap to close and cut off the fuel creating a very weak
mixture. As the throttle is opened, the leak becomes less and less
significant and engine operation appears to return to normal.

  This is obviously only one possibility, but it is very real; the split
doesn't need to be that big - check carefully round any concertina sections
of air trunking where splits may not at first be obvious.

  hope this might help.

  Rich


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<BLOCKQUOTE style=3D"MARGIN-RIGHT: 0px">
  <DIV align=3Dleft class=3DOutlookMessageHeader dir=3Dltr><FONT =
face=3DTahoma=20
  size=3D2>-----Original Message-----<BR><B>From:</B> Rich M=20
  [mailto:rsrich at cwcom.net]<BR><B>Sent:</B> 06 November 1999 =
23:33<BR><B>To:</B>=20
  diy_efi (E-mail)<BR><B>Subject:</B> Re Motronic 4.1=20
  newbie-continued<BR><BR></DIV></FONT>
  <DIV>
  <P><FONT size=3D2>------------------------------</FONT></P>
  <P><FONT size=3D2>Date: Fri, 05 Nov 1999 20:44:33 EST</FONT></P>
  <P><FONT size=3D2>From: "Derek Kaznoski"=20
  &lt;sweetpea1998 at hotmail.com&gt;</FONT></P>
  <P><FONT size=3D2>Subject: Motronic 4.1 newbie-continued</FONT></P>
  <P><FONT size=3D2><SPAN class=3D590433523-06111999><FONT =
color=3D#0000ff=20
  face=3DArial>&nbsp;</FONT></SPAN></FONT><FONT size=3D2>&gt;I took off =
the ISA and=20
  examined it. The valve </FONT></P>
  <P><FONT size=3D2>&gt;seemed to open and close </FONT></P>
  <P><FONT size=3D2>&gt;without difficulty. I went ahead and cleaned it =
with=20
  throttle </FONT></P>
  <P><FONT size=3D2>&gt;body cleaner </FONT></P>
  <P><FONT size=3D2>&gt;to be sure (thanks Dylan). I noticed that in the =
fully=20
  closed </FONT></P>
  <P><FONT size=3D2>&gt;position, </FONT></P>
  <P><FONT size=3D2>&gt;there was about a 3mm gap present, i.e., the =
valve is=20
  over-</FONT></P>
  <P><FONT size=3D2>&gt;rotated past the </FONT></P>
  <P><FONT size=3D2>&gt;closed position. </FONT></P>
  <P><FONT size=3D2>That's right; in the de-energised condition, the =
valve returns=20
  to it's endstop which exposes a default opening which should =
correspond to a=20
  high-idle setting. This is used as a fail-safe to produce a useable =
(if little=20
  high) idle speed if the ISA or it's drive fails.</FONT></P>
  <P><FONT size=3D2>&gt;I'm </FONT></P>
  <P><FONT size=3D2>&gt;planning to replace it. If anyone thinks this is =
a bad=20
  idea, </FONT></P>
  <P><FONT size=3D2>&gt;please let me </FONT></P>
  <P><FONT size=3D2>&gt;know. Any other input is greatly =
appreciated.</FONT></P>
  <P><FONT size=3D2>Before you replace it, check for splits or leaks in =
the air=20
  tubing/trunking on the engine side of the airflow meter and ISA. I =
have come=20
  across a similar effect of rough idle on a LE2 sytem for just this =
reason: at=20
  idle the leak represents a significant bypass round the airflow meter, =
so=20
  allowing the flap to close and cut off the fuel creating a very weak =
mixture.=20
  As the throttle is opened, the leak becomes less and less significant =
and=20
  engine operation appears to return to normal.</FONT></P>
  <P><FONT size=3D2>This is obviously only one possibility, but it is =
very real;=20
  the split doesn't need to be that big - check carefully round any =
concertina=20
  sections of air trunking where splits may not at first be =
obvious.</FONT></P>
  <P><FONT size=3D2>hope this might help.</FONT></P>
  <P><FONT size=3D2>Rich</FONT></P></DIV></BLOCKQUOTE></BODY></HTML>

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