Hello,

I have read a ton of info on tuning a chip and have a good idea of how to do it but one thing still confuses me.

On the diy-ecm website or whatever it is, the spark table is shown with rpm values on the left and kpa values on the right.

HOw is it possible for an engine to create higher amounts of vacuum at the same rpm?

also, how is this achieved for tuning purposes?

 

kpa when not indicated as kpa VAC is alsways more load ie

10 20 30 40 50 60 70 80 90 100 > more load unless
kpa vac which is 100 90 80 70 60 50 40 30 20 10 < less load got that ?

 

so going uphill will apply load tot he engine ehich will require more vacuum to produce the same rpm, right?

 

You get vacuum when the throttle is closed.

When you go uphill you must open the throttle to keep the RPM. You will get less vacuum, more kPa, more engine load, more air.

Atmospheric pressure is 101.325 kPa.
With more engine vacuum you get lower absolute pressure.

 

but, how do i change the vacuum at a given rpm?

 

you dont want to change vacum. you want to change the ve in each field.

1 2 3 4 5 6 7 8 9 kpa
1 hfgyucgucyjchjvgjv
2 xtryxctfgycgycftycty
3 tctfycftcgyjcgyucghj
4 fctyhcftycgyhcftycftghc
5 cftycfgthcghctycgfujyu
6 yrtycftctyuyuvfgyedry
7 tycftytycftycftucyucygu
8 ctuyctyucftucuyuvhu
9 hhcftgcuyfguvrtxrdtt
rpm

see all the garabage i typed in there thats the data field. vacum cannot be changed in the code. it works like this.

ecm sends out 5 volts. map sensor sends back 2.5 volts. ecm reads 2.5 volts as 55kpa. ecm looks up 55kpa x 2500rpm if that value in the table is 33 then it uses 33 to start its equation. theres alot of filtering but the ve table is the most important fuel table in the ecm.and it doesnt essentialy use vacum. thats just a human readable term for us.

 

Thank you so much for clearing that up, now i can finally tune my ecu and start rippin up the drags. lol.