24s2k7

Here we go again!

So, say I have VAFC. I go get it dyno tuned with great results. Then I set the VAFC to only correct a/f ratios when I am at 80%throttle and above 6000rpms.
I drive around all day, just cruising around. The vafc never corrects anything because I never get on it. Then one day, I decide to tear it up. I get my above 6000rpm and 80%throttle. So the VAFC kicks in and corrects the a/f ratios, giving me more power. I do this for a few weeks. Will my ECU learn this piggy back system?
Doesn't the ECU only learn in closed loop? Since the VAFC only comes on in open loop will it still negate the changes after time?

ScottyBallistic

First off , Kayvan it was great talking to you last night . I am glad we can be more civilized than our first encounter . I hope I was of help and you came out of it with some good info . Hope to talk to you again ( don't give away any of my N/A tricks )


First off Throttle position is only part of the equation when it come to fuel and timing maps . Manifold pressure , water temp , intake temp on what the ECU uses for Fuel and timing .
Now, the way these units adjust fuel is by altering the signal that is sent from the MAP sensor to the ECU, thus giving the ECU a false value to fool it into giving a different amount of fuel. In small quantities, this is fine, and won't make a big difference. however, note that since one axis of the timing tables is air flow. therefore, if you were to lean out your settings (hence telling the ECU you are flowing LESS air) you will get more timing. Although more timing at the right time is GREAT, other times it is not so desired. when you lean the settings in large amounts you are pushing the ECU maps into lower cells on the map than they would normally be for the actual airflow, so you will end up with KNOCK due to more timing advance than what should be in certain cells of your map.Now the ECU see Knock and pulls timing back out and again now your settings are incorrect for the situation . ( Their are reason people pay good $$$ for tuning a e-manage or AEM is to work out bugs like this .

Air and water temp also effect timing also in which the VAFC can not see and adjust for . But the factory ECU is constantly changing maps for . ( Just sitting in traffic will change map settings , heat soak being a concern . Ever have you car feel slugish after sitting in traffic??.It because your fuel trim hasn't adjusted for it yet . Once it has adjusted for the traffic and heat and you get on the highway you car seems like it lacks power again till you make a few runs and the ECU adjusts back for its current Air temp and MAP settings . AIT has a big effect on this ) depending how long you have been in traffic your longterm fuel trim will adjust for that then when you get out of traffic and get on it your VAFC will me manipulating a MAP that it was not tuned for .

Your VAFC only has 24 points of fuel control 12 being low and 12 being high ( =12x1 sense their is no timing control ) You are controlling 6000rpm to 9000rpm so you have 3 pionts per 1000rpm to control .Thats every 300 rpm other than that its just guessing what do do inbetween .

A EM-ultimate, AEM ,Haltech ,megasquirt etc have 16x16 fuel and timing tables and up ( I have seen 32x32 tables ) . Why because it is needed to do the job properly . It also read Air temp and water temp in makes its choices on what to do .Your VAFC is like adding a carburetor traits to your fuel injection . Although the carburetor works in running a engine, it is very crude and very limited to tuning .( we have a twin turbo 68 Cobra with a carburetor in our show room which will soon be getting fuel injection with a MegaSquirt EMS . The cobra is a on/off switch with its four barrel carb . It has very bad part throttle transitions in and out of boost .Very dangerous in a 2200lb car. Once Fuel injected it will be like driving a Porsche twin turbo very smooth ) Thus the reason for Fuel injection .

Another example of a VAFC to a proper EMS system , is like 87 oct to 93 oct gas . Even though your car will run on 87 you alway use the higher , why? Because it is recommended for your car not to knock and pull timing. The same thing will happen with your VAFC .It will cause you hit the limits of the map that the ECU has chosen for it given situation thus pulling timing to control knock . A Vafc will have more benefit on pre OBDII car that don't use O2 feed back or distributor type ignitions where you can adjust base timing to try and control knock .

I don't get it sometimes , People spend money on the best header, intake , exhaust etc with no concern of cost then try and tune it with a inferior and crude fuel controller because its cheaper . FYI engines are not cheap . Not saying you will destroy your engine but you are on the right path .

You know the saying all show and no go , that is a VAFC.
" ooh look at the pretty lights "

If you need show point with the locals just mount your AEM EMS on the dash , I bet you will get more looks and respect .

A VAFC is a ricer toy , step up to the big leagues this isn't kansas anymore .

I can keep going but I would just be

Thank you too those that understand and I will pray for the ones that don't .Check on ya all later I have cars to build