BARO creep in 2 bar

[mistermike]

I've got the 2 bar up and running nicely. (Fantastic job, guys!) I have the BARO update enable at 12K, disable at 12.8, but it's still creeping up. At key-on, baro is pretty close to engine-off MAP, around 98-100 kPA. After some spirited driving, it winds up at 104.4 Perhaps I've overlooked something.

[GMPX]

Mike,

For the sake of everyone else I'll respond to your Emails here too.

The reason it updates when you drive is whenever the PCM sees MAP above Baro then it updates the Baro value to the highest the MAP reached.
There is however a limiter coded into the PCM to stop Baro updating above 104.9kPa.
However, look at table {B0304}, you can see that at 105kPa Baro the PCM basically makes no changes, it is the same for 100kPa, 104.9 is the internal upper limit in the PCM for Baro updating, as is 60kPa the lower limit. Look at {B0304} at 65kPa and the factor is quite low.
What does occur with Baro problems is usually at cranking.
The PCM updates the Baro on steady state throttle or WOT and on engine shutdown. You normally see the major changes on the shutdown update.

You will find because of the PCM's limiter to 104.9Kpa for Baro with the factor at 1.00 for adjustment at that point it will have little impact.

Cheers,
Ross

[mistermike]

Once again, terrific info. Thanks!

[TAQuickness]

I'm having trouble putting 2 and 2 together here...

What is the purpose of the GM.BARO parameter for the PCM?

[GMPX]

Do you mean what is the purpose of the Baro compensation?.

Cheers,
Ross

[TAQuickness]

YES!

I've been racking my brain as to how the PCM would use barometric pressure. I suspect it somehow effects fueling, but I can prove and disprove that on paper.

[joecar]

One way the PCM uses BARO is to calculate (BARO - MAP) to index the IFR table.

[GMPX]

That's right Joe, it uses Baro for some table lookups and to calculate manifold vacuum....and to compensate fueling when cranking.

Cheers,
Ross

[TAQuickness]

Is it accurate to say that barometric pressure indirectly effects fuel calculations?

[mistermike]

Your IFR table references manifold vacuum, but from what I'm gathering, the 5% or so shift isn't going to create a lot of drama. It throws off my boost calc. PID a tiny tad. "({SAE.MAP}-{GM.BARO})*0.14504" if you want to see it in PSI.

[TAQuickness]

shouldn't be a big deal at all, but, in case you've been following the MAF thread on ls1tech, this sorta proves my theory of the PCM compensating for humidity in both SD and MAF mode.

Emphasis on the sorta...