Fuel Map % Adjustments

[Robbks]

Just a quick one.

When adjusting the fuel maps in the interceptor it's shown as a percentage (Fuel Correction %)
What is it a percentage of? (injection time (ms), actual fuel flow, AFM voltage, etc)

In my case i went to 15% larger injectors (380cc> 440cc) but only needed a -6% change in fuel correction for the same AFR?

[Ignition]

edit: my bad forgot I was in the Interceptor section

[Robbks]

Reason is, i'm trying to work out a rough starting point for a mates map given the AFR's he's currently running and the difference in injector size to the new injectors.
We just need to throw a quick road-tune over the fuel maps only to allow for the extra boost on a bigger turbo and injectors (stock ones are well maxxed out)

EDIT:
*cough* Adrian...?

[vosadrian]

The percentage is a percentage change to the load signal. In most cases this is applied to a voltage output from a sensor like the air flow meter. So for example, if running an air flow meter with 0-5V output, and the MAF input of the interceptor is set for 0-5V, then if the signal is 3V, and you apply -10%, it will take away 10% of 3V which is 0.3V so you get 2.7V output.

The thing is that MAF sensors are most often not linear... normally logarithmic. This means that a small change in air flow at low flows has a much bigger change in voltage than the same change in air flow at higher air flows... so a 6% change in voltage at full boost, high RPM can have a big change in the flow perceived by the ECU, but at lighter loads it will have a lesser effect. When changing injectors, you generally apply a global percentage correction to get it close at high loads, but the best way to tune light loads is to get a scan took and look at the fuel trims in the ECU, and adjust the fuel maps in the interceptor until you get close to 0% fuel trims.

Also remember that pulling fuel out due to bigger injectors (or any other reason) results in the ECU thinking there is less load on the engine then there is, and therefore it will advance the timing... so you should then go and pull timing in map areas where you have pulled fuel (unless the engine want more timing than OEM ECU).

You have to think the way the Interceptor thinks. It does its tuning on the input sensor signals to the ECU... MAP, MAF, Crank sensor. Any changes it makes are done based on percetages of these signals.

-- Adrian

[Robbks]

Nice work adrian, the exact info i was looking for. (which also makes a lot of sense, and will help with tuning the other car)

and now just looking back over my maps, i can see that i've only got small corrections at the high load sites, and much larger ones in the areas of vacuum and mid-range rpm for teh right loads.

I always tune areas that are normally controlled via o2 feedback with the sensor unplugged so it's not interfeering with the fuelling (i don;t have the appropriate scanner or ECU definitions (for evoscan) for the early TT to be able to see the data)

[ovaxitd]

is there a sectoion i am missing with the miniceptor that you can have a base % when putting in larger injectors or if they are say 10% larger you need to adjust the mapping to -10% and tune from there. If you know what i mean? i am aware of pfc and other standalone ecus being able to handle this but unaware of the intercetor feature.

cheers

[Robbks]

No.
there's no "blanket" correction/ scale that can be applied like the PFC (i had one of those in my previous GT Forester)
you simply have to re-tune the whole map.

When i put in my larger injectors, i did a run through the rev range at a fixed load (0psi) to get a baseline of how much extra fuel was in it.
i then removed some of the correction (say -3%) and then did another run at the same load until i had a ballpark figure of where the fuel map needed to be.
I repeated this for 5psi, 10 psi and 15psi

this then gave me most of the map covered,
adjusted/ linearised the intermediate values and it was all pretty close.
a few more runs to check WOT and light throttle parts of the map and it was re-tuned.

i still do a few adjustments here and there as i notice it may be slightly rich in one particular area or just doesn't feel as responsive as a certain part of the map, but that simply comes with time spent logging and driving on the road

[clarkdeu]

VVTI on the supra is not something you can experiment with because it can lead to serious engine damage in a heartbeat.
The theory behind VVTI is to vary the intake cam timing continously based on load and rpm. It's basically the best of all worlds cam timing wise. You can actually feel the difference on a non VVTI vs VVTI motor torque/horsepower wise. It widens the torque/power band mainly in the low and midrage rpm areas.VVTI on the supra is not something you can experiment with because it can lead to serious engine damage in a heartbeat.
The theory behind VVTI is to vary the intake cam timing continously based on load and rpm. It's basically the best of all worlds cam timing wise. You can actually feel the difference on a non VVTI vs VVTI motor torque/horsepower wise. It widens the torque/power band mainly in the low and midrage rpm areas.

[HaltechMatthew]

Having a bad day Clark?

Brought back a post from the dead (June 2010), double pasted into the message, and it looks like it is in the wrong section??? That's 3 strikes and you're out!!!