[Diy_efi] MAP vacuum signal isolation?

[Becker, Damon Damon]

I'll weigh in with my experiences.  

I NEVER tee a MAP line.  It introduces potential reliability issues into
a mission-critical sensor's vacuum signal.   The other reason I don't do
this is I want to minimize the length of tube to optimize the MAP
sensor's reaction time.  Believe it or not, longer lines do make a
tangible difference during transient manifold pressure conditions.  

As for the vacuum advance diaphragm, I would imagine the answer is yes,
it creates interaction issues in your setup.  

As for where to tap, do NOT tap near a runner in the plenum!  You will
get an oscillating signal, even if you aren't on the runner itself.  You
just have to be close.  You need the tap in a deep, dark corner of the
manifold away from the runners for a smooth-as-possible vacuum signal.  

Those are my thoughts.  

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of Geddes, Brian J
Sent: Tuesday, January 24, 2006 10:37 AM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] MAP vacuum signal isolation?

I think the answer is "yes", but I'll be curious to hear some opinions.


But, I'd like to expand on the question a bit.  Where is the ideal spot
to source the MAP signal from?  On my V6 setup, I am sourcing my MAP
signal from what used to be a crankcase ventilation passage, which
connects to all 6 intake runners about an inch upstream of the intake
valves.  Would it be better to source from further up in the plenum,
like just after the throttle?  Or does it matter?

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of pparaska at comcast.net
Sent: Monday, January 23, 2006 10:35 PM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] MAP vacuum signal isolation?

I'm running a Megasquirt-I with a Holley Pro-Jection 4bbl TBI.

I've been grabbng the vacuum signal off of a line from a full time
vacuum source on the front bottom of the TBI (below the throttle plates.
I share that source with a vacuum advance can on the HEI distributor,
through a T in the hose coming from the port on the TBI that splits off
to the MegaSquirt's MAP sensor and also to the HEI vacuum advance can.

Is there a problem with this kind of setup?  Could I be getting strange
signals to the MAP sensor while the vacuum advance can is changing it's
volume (diaphram moving)?

In general, is it better to feed the MAP a signal straight from a
manifold plenum that is removed in distance from the power brake booster
and other vacuum ports (Vac advance, etc.)?

TIA,
Pete
http://AlteredZ.com
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