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Improving Fuel for Economy and Power
In this section I have already partly explained how to tune for economy in The Tips and Info section A Look at Calibrating, Page 3.
Setting the VE's first
This section explains how to set the VE's manually. See VE UPDATE to set VE's automatically.
If you use the VE Update function, you will most likely still need to do some manual editing as well.
What I've been calling the Main Fuel Map is in fact the VE map or No. 124 FUL:OUT:VE to be precise, and as the name suggests VE stands for volumetric efficiency. So this map isn't in fact the fuel map, it's the VE map.
There are 3 parts to the fuel equation. First there is the BPC (INJ:RAT x CYL:SIZ). This is determined by injector size. Then this is multiplied by the VE percentage, and finally this is multiplied by the (commanded) Air Fuel Ratio which is normally preset and usually doesn't need changing. These 3 factors determine the final Base Pulse Width. Change any of these 3 factors and the bpw changes.
Therefore, once the Injector size is determined and the AF Ratio set, from there you only adjust the VE map.
The Delco system runs in Closed Loop once a few parameters have been met. Closed loop means it is in self learning/tuning mode which is controlled by the oxygen sensor.
There is a term called Stoichiometric which means 14.7 to 1 air/ fuel ratio. This is the air/fuel ratio that fuel burns "correctly" at (in laymen's terms).
The calibration is set to read at 14.7 when in closed loop at No. 100 FUL:RUN:STOICAF.
For the system to enter Closed Loop (that is once the engine has warmed up etc and the parameters have been met) the a/f value obtained from the FUL:OUT:RUNAFR table must be equal to FUL:RUN:STOICAF.
So if both these values are 14.7 then the system will run in closed loop.
Generally the system is set to run in Closed Loop 14.7 from part throttle to approx 3/4 throttle, and then at idle approx 14 to 1, and then from 3/4 to full throttle as rich as 12.5 to 1.
If the system is running outside of 14.7 ie a different a/f of say 13 to 1, then it goes into Open Loop and stops trying to retune itself to 14.7. It then relies on the air/fuel ratio alone for fuel requirements and then providing the VE's are correct at the associated load points it will be running at 13 to 1.
Now if the VE isn't correct at any given point in Closed Loop, the oxygen sensor will pick this up as either a rich or lean condition and try and correct it .
Have a look at the Gauges Screen again and notice that the A/F ratio is 14.5. This is at 33.8 kpa Manifold Pressure ( no load--high vacuum) at nearly 2000 rpm. This is in Open Loop at this point and the STFT units is fixed at 128. ( 100% IN SP3)
You can tell if the VE isn't correct in Closed Loop by watching the Short Term Fuel Trim gauge (STFT) on the Gauges Screen. If it reads under 128 (100% SP3) it is rich, if it reads over 128 (100% SP3) it is lean at that load point and is corrected by sliding the appropriate VE bar up or down at that load point.
Slide the bar up to richen the VE or down to lean it out.
The object is to set the VE's at all these load points in Closed Loop to achieve actual 14.7. To do this the STFT Gauge would ideally read 128 (100% in SP3) at all these points which is very difficult to get exactly right, however within a couple of points is considered close enough
Note: In Open Loop, if the VE's are wrong, you have no way of knowing unless you use a Wide Band Oxygen sensor. Just because the commanded A/F Ratio says 12.8 : 1, it doesn't mean to say that's what it is.
With a A/F meter you can adjust the VE's until the A/F meter shows the same as the Commanded A/F Ratio.
Another way to do it, but not as good, is to change all the A/F Ratios in FUL:OUT:RUNAFR to 14.7.
In theory you can tune these A/F's this way without having a tailpipe A/F meter, but it is not advised, as your VE's could be way lean and engine may detonate.
Hopefully now you're getting the hang of how the VE's work and how to correct them, but how do you go about it.
The first thing you have to do is Disable (turn off) the Block Learn Mode. To do this go to No. 11 GEN:OPT:EOPTCA and you will then see 8 buttons there. Simply select "disable blm" and set it (push in) and save.
What this does is it prevents the self tuning part from making any corrections.
The next thing is find a nice quiet piece of road where you can be driven at steady speeds. You don't have to go fast, but you need to drive at constant speeds.
The Load Points in the VE maps are in increments of 400 rpm and 10 kpa so what you should try and do is hold the engine speed at say 2000 rpm and then adjust the throttle to get the different kpa readings and then see what the STFT readings are.
You can do Data logging to do this, but I find it easier to do it this way using the Gauge Screen.
I make a chart with the 10, 20, 30 etc kpa readings across the top then the rpm's down the left side in rows and columns, then photocopy a bunch of them and have them on a clip board. When you are driving or being driven you can write down quite a few different readings at a time without having to remember them. Then you can flick back to your VE's from your Gauge Screen and make the adjustments and then save and then start again with a new page. It's amazing how much you can get done in 1/2 an hour.
Tuning A/F ratios for Economy
Once you have the VE"S done you will notice how crisp and responsive the whole range is and also this improves the economy.
A new feature in Street Pro 3 normally found in much later factory software, is a feature called Lean Cruise Mode. What this does is after a set short time of cruising within a certain rev range usually from approx 1800 to 2400 rpm at approx 50 to 70 kpa MAP pressure the program switches to another table and then runs from approx 15 :1 to 17:1 A/F ratio. To turn this feature on Select 11 GEN: OPT: EOPTCA and press LEAN CRUISE
Be Warned though before selecting this feature, make sure your VE's are 14.7:1 at these points at first. The amount of change in Air/Fuel Ratio you change is at 110 FUL:LNC:DELAFR. Then do some fairly long runs at these points in this map and select Track to familiarize yourself with these loadpoints and feel how much the engine is working. Then go back to the LEAN CRUISE button and switch it on and off. If you can feel a difference, it is too lean. You can have up to 3 points of Lean Cruise at the lesser load points, but back it off to about 1.5 to 2 as the load increases. You shouldn't be able to feel any difference between on and off.
Tuning A/F ratios for Power
If your VE's are right at the higher MAP readings the A/F ratios should be reasonably accurate at these points.
Remember if your A/F isn't showing 14.7:1 then the fuel calculation is worked out by the A/F ratio showing multiplied by the VE, so if the VE isn't right then the actual A/F could be anything.
Surprisingly this isn't altogether that bad so long as it isn't detrimental to performance or the engine.
This may sound a bit sloppy but with an A/F meter shoved up the rear (hey watch it!) if the reading is 13:1 but your gauge is showing 11:1 (commanded) it doesn't really matter. As I said earlier it means your VE is out and I usually correct this here.
Note here that this is providing your Injector BPC is right. See Injector Size.
Something to be careful of here is that Oxygen sensors are more accurate with lean readings than rich, that is from 14.7:1 and higher they are more accurate. This applies to A/F meters as well.
So its hard to say tune an A/F of 12.8.
Also there is no set best A/F that makes the best power. Every engine is different. Don't you get sick of hearing that…….So what do you do.
Well the old ways are the best, that is, suck it and see.
First of all the easiest way is the age old "read the spark plugs" after doing a power run. The hardest thing with this is though, at what revs was it lean and what revs was it rich.
The best way to find this out is on an engine dyno . It's virtually impossible to feel it in the "seat of the pants"
I usually aim around 12.5:1 to 12.8 and then start on the Ignition timing.
In my experience I have found that providing the VE's are accurate, the factory set A/F's are pretty good.
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