i am in the process of retuning my car,91 vette, i am usung datamaster for datalogging. mainly im tring to eliminate a rich problem. in the datamaster program im mainly looking at the map sensor readings to determine where i need to make changes in the ve tables. my main concern is at idle im around 50kpa is this normal for a fairly large cam.

 

ok.. basicly i keep pulling fuel out until i have optimal readings at idle. 128 blm. but i really cant test higher rpms until i drive the car. what im tring to do is figure out how to convert the map sensor kpa into the numbers used in the ve tables.

it the ve table the ve vs. rpm vs. map reads from 100 rpms to 5600rpms. and from 20 to 100 for the map. i need to find a way to convert the 20-100 map readings to kpa or hg..

 

I'm sure you'll get some responses on the Scan and Tune board.

Jake

 

No, no, no, VE table numbers are not Kpa number. Think to the number in the ve table like a percent of volumetric efficiency .
Higher the number higer the fuel added.
the 20 to 100 map readings are from 20 kpa to 100 kpa.
So, think to be at 60 map (= 60 kpa) at 1600 rpm and you have the vale of the VE table of 70.31.
At this level of load (60 kpa) and rpm (1600) you blm is say 108.
at 108 the ecm is REMOVING fuel to stay at 14.7:1 AF ratio.
You need to lower the fuel supplied = you need to lower the 70,31 value.
how much?
108/128 = 0.843
multiply 70.31 to 0.843
= 59.32
change the value of 70.31 to 59.32 and you should be close to 128 blm
-Beppe-

 

i understand how to pull fuel out, but are you saing that that kpa readings that im seeing in my datamaster software does not compare directly to the ve tables?

example... at idle im at 55kpa.. and after lowering my whole ve table by 10% im still at 120blm.. that 55kpa that im seeing at idle will not directly point to the 55 value in my ve tables at that rpm..

if it does great.. if it doesnt where do i look...

 

I need to understand...
you idles at 55kpa? with gear inserted? or in N or P?
Which kind of editor you have tunerpro?, tunercat?
My stock bin say at 55kpa at 700 rpm a value on the Ve table of 66.41.
if at this load-rpm (55 kpa-700 rpm), i'm at 120 blm (I can see this using Datamaster when the engine is idleing..), I need a correction of about 7% on the ve table, i will lower the value of 5% on the perfect cell (55 kpa - 700 rpm - the 66.41 will become about 63) and about 2 or 3% in the surrounding cells. (60 kpa-700 rpm, 50 kpa -700 rpm, 55 kpa-600 rpm....etc..).
I burn the new chip with these new idle VE values changed.
I run datamaster connectet to the ALDL with the car idleing and I look at the blm value at idle ..
Now I should see a value near to 128.

You say " example... at idle im at 55kpa.. and after lowering my whole ve table by 10% im still at 120blm.. that 55kpa that im seeing at idle will not directly point to the 55 value in my ve tables at that rpm.."
you will NON change the level of vacuum your cam/intake is changing ve values!
There is any relation between the 55 kpa and your value of 55 in the VE table.
Your car still continue to idle at 55 kpa.
If you have a value of 55 in the Ve table at 55 kpa/your idle rpm and you are at 120 BLM at map 55/your idle rpm , you need to lower you 55 VE value to a lower number (53.. 52....).
let me know!
-Beppe-

 

i am using tunerpro.. and yes i am at 55kpa at idle.. in neutral

at idle, 900 rpm's ,in the ve tables at 55kpa my value is 50.56. and blm is 120.. so i multipied the whole table by another 5% to get value of 48.03. this will take care of my idle richness. but what if i drive the car and the rest of the table is to lean? do i have to change all the values one block at a time based on my datamaster data..

one other thing.. my target a/f ratio is set at 14.7/1. craig moates said that i can lower that value if i want the computer to shoot for a different a/f ratio. like 13.7/1.. have you tired this?

 

You should tune your idle with gear iserted, because your tipical idle will be when you are in traffic or at the traffic ight. Your idle should be about 60 kpa at 100 rpm less.
The best way (my preferred) is to tune the idle first (as mentioned above) then take the car for a long run using all part throttle situation with various map values (kpa) with various rpm.
When you have all various data from your datamaster datalog, you can do the same for all kpa values/rpm values.
Be careful to do not using too much throttle to call for PE (power enrichment mode).
You can do it manually or (strongly suggested) you can use VEmaster. Its a tool (free on internet) to tune the ve tables via .uni file from datamaster.
Don't be afraid to be too lean during part throttle situation until your blm is under 160. Under 160 values are managed without problems by the ecm.
I will never change the 14.73 constant (IMO) even having a WB o2 sensor.
To tune WOT situation (please DO NOT use vemaster for map values over 90 and for rpm values over 3000 rpm),
you need a WB O2 sensor or if you can't afford it you should see the MVolts o2 values at wot.
-Beppe-

 

i have a 6speed so my idle is always at 850-900. i have a wideband in the car already used to tune my nos setup so that will help wot. i also have vemaster but i dont have enough data to use it yet..

thanks for your help. i think i got it now....