Bernd,
Thanks for the clearup. I think you should fix the
website, since it says: "Under boost, they give a false
reading ("freak out") and register 30.8"hg instead of 1-
0"hg."
While I don't debate that the computer may freak-out,
it's reading of 30.8"hg (that it shows through the OBD-II
port) IS just 2"hg above it's 'engine-off' reading of 29"
(at least today) atmospheric pressure (or 1" off the
29.92 that is standard for sea-level). 2"Hg is less than
the barometric pressure can fluctuate, so a reading of
30.8" should be a valid value (it is equivalent to being
about 500ft below sea level), or possibly in the middle
of a big storm. I don't undestand exactly why the
computer would freak out.
In any case, adding a 4.5v zener-diode between the sensor
pin and ground should prevent the reading from ever
getting up above 29"Hg (nominal atmospheric pressure)
while still allowing everything to work normally
while the engine is under vacuum, and seems like a lot
simpler answer than bringing the TPS into the picture.
(Please remember that all the numbers above are relative
to absolute vacuum, not to normal atmospheric pressure). Also, I fully believe that your method works, I'm just
trying to understand why a $0.20 diode wouldn't work just
as well.
Perhaps there's something I still don't understand though.
Thanks,
.Geoff
-----Original Message-----
From: owner-dakota-truck@buffnet.net
[mailto:owner-dakota-truck@buffnet.net] On Behalf Of Bernd D. Rasch
Sent: Tuesday, October 23, 2001 21:02 PM
To: dakota-truck@buffnet.net
Subject: DML: Re: ATTN Bernd: MAP Charger/Bypass
Geoffrey,
0"hg should read 0" vacuum (confusing and not quite accurate wording).
At idle, you have (on the average) 16-18" vacuum. The more you press
the throttle, the less vacuum you have...works on a linear scale. WOT =
0" vacuum (again, slightly wrong wording on the website).
What the MAP charger does (not the Map/Boost Bypass - they're two
different things) is simple:
At WOT, you have approximately the same voltage at Key ON/Engine OFF ("0
Setting"). When you're under boost, the 1-BAR MAP doesn't understand
the positive pressure and continues past the "0 Setting" (also the same
at WOT)...literally "freaking out" the PCM and it leans out slightly.
Now what the MAP Charger does is override the out of range MAP reading
and set it to the "0 Setting" or slightly below. It's activated by TPS
position and you can adjust the ON/OFF (bypass voltage as well) to
whatever you want.
It works and has been working on a test truck for the last several
months (about 6 I believe).
- Bernd
-----Original Message-----
From: owner-dakota-truck@buffnet.net
[mailto:owner-dakota-truck@buffnet.net] On Behalf Of Geoffrey Hausheer
Sent: Tuesday, October 23, 2001 12:41 PM
To: dakota-truck@buffnet.net
Subject: DML: ATTN Bernd: MAP Charger/Bypass
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