combined afr/ve in other fuel section

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89gtar
MegaSquirt Newbie
Posts: 2
Joined: Wed May 10, 2006 11:00 am

combined afr/ve in other fuel section

Post by 89gtar »

hello! I have a question regarding the combined ve/afr tables in the other fuel box
i am running an ms2 ver 3 2.89 code and have it tuned out pretty close but i went to swap this option to seperate ve and afr and it died instantly.
Does this mean i have to re-tune all those ve numbers again? it seems obvious but i just wanted someoneelses opinion on it, thanks :yeah!:
3rd gen Transam with 355ci 6spd manual MS2 version3 2.89B&G
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Bernard Fife
Master Squirter
Posts: 475
Joined: Thu Oct 29, 2009 12:54 pm

Re: combined afr/ve in other fuel section

Post by Bernard Fife »

Does this mean i have to re-tune all those ve numbers again?
89gtar,

Basically, yes.

When you separated the tables (to use 'separate VE and AFR tables'), you need a different VE table. The combined table was effectively VE(rpm,kPa)*AFR/stoichAFR. In the new table, the values in the VE table are just VE, and the values in the AFR table are just AFR (obviously).

You could recalculate the VE table to make sure that newVE(rpm,kPa)= oldVE(rpm,kPa)*(tableAFR(rpm,kPa)/stoichAFR), then you shouldn't have to re-tune.

For example, if at idle the old VE was 45%, and in the AFR table you put the idle AFR at 13.5:1 (and using gasoline), the the new idle VE at that table cell would be: 45%*(13.5/14.7) = 41% The VE table value is lower because the AFR table will richen the fuelling (by 14.7/13.5).

But it might be simpler to re-tune.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it.” - George Bernard Shaw
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