92 corvette tuning tips and questions.

[steveo]

it doesn't populate VE it only puts BLM in the table.

one thing you need to understand about tuning fuel is you're rarely populating a table with new values, you are adjusting the existing values based on feedback.

in simple terms the ECM says "5!", but your o2 sensor says "...but we had to add 2% of fuel there" so you might change the value to "7" and then try again.

in real terms, since you're tuning a VE table, the ecm actually says 'for 2000 RPM and for 50KPA of MAP, the engine is 43% efficient'.

it then injects its fuel on the assumption that the engine is actually 43% efficient at that RPM (there are other things affecting fuel but just worry about the VE table for now)

you then get feedback as a BLM from the trim system that says "trim in this area is 150"

since 128 is 0% trim, we can calculate the trim as 150/128=1.171 (17%) (in other words 150 is 17% higher than 128)

so the ECM had to add approx. 17% extra fuel to achieve the proper mixture.

since we had to add 17% of fuel, we can assume that instead of being 43% efficient at that RPM/MAP value, it is actually 50% efficient. so you could change that value to 50.

but a better way to tune would be to get multiple data points from that area and average them together, because big piston engines are not a precise instrument.

you then have to 'interpolate' or 'guess' the values to smooth the table in between your adjustments, because there's no way you'll have good data for the entire table.

if this sounds time consuming, and like it's something a computer could do for you with way less effort, that's why i wrote trimalyzer (but then you have to learn to use that properly, too, and have some common sense in case it makes a mistake.)

the other reason tools like trimalyzer are good is because you can't always trust trims, you can only trust them once you are in closed loop, and the engine is warmed up, and you aren't in power enrichment, and whatever else. trimalyzer is good at filtering data.

edit: it's also good at taking HOURS of logs and crunching the whole thing...