<VV> RE: MAP sensor - utlimately for a Corvair

[BBRT]

Thanks to both of you, Craig & Jim. Heh, heh...now we know where there are 
at least two guys who are involved with sensors.
Chuck S

----- Original Message ----- 
From: <burkhard at rochester.rr.com>
To: "Craig Nicol" <nicolcs at aol.com>
Cc: <virtualvairs at corvair.org>
Sent: Thursday, October 25, 2007 2:31 PM
Subject: Re: <VV> RE: MAP sensor - utlimately for a Corvair


>I agree with Craig except the part about the BARO estimation being off
> if you drive up a mountain after starting at sea level. I don't have
> knowledge at how every company does it, but at least SOME of them (and
> I'm betting most if not all) do have some pretty trick algorithms that
> can relearn the BARO estimate without shutting down the engine if it's
> suspected that BARO has changed a lot since the original determination.
> At one time, it's possible that this could have been a (minor) problem,
> but not really anymore.
>
> Also, not all the new ECMs have on-board BARO sensors. Some still
> figure BARO from the MAP sensor at keyup and then update when
> the "sense-checking" suggests a relearn is required.  It all depends on
> what the OEM is willing to pay for.  :-)
>
> Jim Burkhard
>
>
> ----- Original Message -----
> From: Craig Nicol <nicolcs at aol.com>
> Date: Thursday, October 25, 2007 2:16 pm
> Subject: <VV> RE: MAP sensor - utlimately for a Corvair
> To: virtualvairs at corvair.org, chsadek at comcast.net
>
>> Chuck asked:
>> <snip>Manifold Air Pressure sensors used on more modern cars sense
>> vacuum in
>> the manifold as I understand it. Some are mounted on a firewall
>> with a
>> vacuum line to the manifold.
>> Questions. What voltage is supplied and what voltage range vs.
>> vacuum range
>> do they sense? What is the reference? Absolute or ambient? If ambient
>> pressure, how does the sensor get it? Is there a port on the sensor?
>> Thanks Chuck S. BBRT <unsnip>
>>
>> Craig Replies:
>> The common GM sensor senses ambient (baro) at Key-on and this value
>> (voltage) is stored in the ECM as "BARO".  There is no separate
>> port for
>> sensing barometric pressure. Sensor variations after engine start
>> (caused by
>> the engine operating) become the MAP (Manifold Air Pressure)
>> value.  Note
>> that this value is always a pressure - the concept of manifold
>> vacuum is not
>> typically used or relevant anymore.  The weakness of this sensor
>> setup is
>> that BARO remains fixed in the ECM until the next key cycle, so if
>> you start
>> in LA and drive to the mountains, the LA value is still the
>> supposed BARO.
>>
>> Newer ECMs have on-board (literally) baro sensors that track the
>> actual BARO
>> value.  GM MAP sensors are available in 1-bar (for NA engines) and
>> 3-bar
>> (for turbocharged engines).  They both run off of a regulated 5v
>> signalthat's sourced and monitored by the ECM.
>>
>> Craig (Now you are talin' my bread and butter) Nicol
>
> _______________________________________________
> This message was sent by the VirtualVairs mailing list, all copyrights are 
> the property
> of the writer, please attribute properly. For help, 
> mailto:vv-help at corvair.org
> This list sponsored by the Corvair Society of America, 
> http://www.corvair.org/
> Post messages to: VirtualVairs at corvair.org
> Change your options: 
> http://www.vv.corvair.org/mailman/options/virtualvairs
> _______________________________________________