Pixsurguy

OK guys - I've read a ton of the posts on this excellent forum, but now I'm even more confused that I was to start with.

The stock S2k ECU supposedly "learns" duirng engine operation and at least in some cases will basically negate the value of some modifications. I understand that that may well be the case as to exhaust system/ header/ throttle body/ cold air intake.

How can we tell if that has happened or is happening, w/o before and after dyno testing and then continued dyno testing to see what the ECU has "learned"?

Is the answer an after market ECU? Only one I've heard about is the Mugen and maybe the one that Comptech provides with their SC. Anybody else sell them for our engine?

Is the "best" answer a VAFC combined with a lot of dyno work to handle the rich/lean problems?

Hope one of you guys who are smarter than me (should be lots of you out there) can shed some light on this. Thanks in advance if you can.

John Nader - Louisville, KY

4373

Spoon sells an ECU for $1600, Feels and Amuse do also, but I don't know the prices or too awful much about ECU's, but when you get your questions answered, could someone tell us if a new ECU is plug & play, or is there programing and things that need to be done buy a certified mechanic?

Pepe

The ECU can only adjust timing/mixture based on the input from sensors when you are not at wide open throttle (WOT). At WOT the ECU uses maps already stored on it so don't worry about this with a few bolt-ons.

Extensive mods (cams, SC, etc) may benefit from a VAFC.

ultimate lurker

All, I have posted some pretty detailed stuff on this, so a search should yield results.

The ECU does learn, but it won't necessarily inhibit performance from breathing mods. Essentially, when it comes to A/F ratio, the ECU is trying to keep it within a set range. If a modification increases airflow, the ECU will see a lean condition and add injector pulsewidth to get back to normal.

Pepe is correct in pointing out that this learning can only take place at part throttle, closed loop operation. However, what the ECU learns during closed loop is applied to open loop maps as well.

Where problems arise is if we try and change the A/F ratio to increase power. Hondas, the S2000 included, are noted for running kind of rich, especially at high rpm, WOT operation. Thus, leaning out the mixture can help. However, the ECU doesn't like this, and if it sees leaner mixtures, it will add fuel, bringing the A/F ratio back down. This sort of thing happens when you try and change fuel pressure, etc.

Now, lets say you put a header on the car. It improves breathing, and also causes the engine to run a bit leaner. So, you've improved power two ways. Now, the ECU sees a leaner mixture, so it richens it back up. Now you lose the power gained from mixture, but you still have breathing benefits.

UL

Pepe

From experience on the dyno I have found that if I change the A/F by way of an adjustable pressure regulator (FPR) the new dyno numbers are constant from pull to pull.

I'm pretty sure the ECU will compensate the mixture change at idle and part throttle but the data showed that at WOT the car maintained the A/F, thus providing the same dyno results after the mod was done.

Schatten

UL - I understand adding a header increases breathing, but how does it cause the engine to go leaner?

ultimate lurker

Try it again later Pepe. Back to back on the dyno you aren't out driving the car around at part throttle giving the ECU a chance to adjust the fuel trim. Also, you may be compensating for a problem the ECU would have handled anyways (such as the overrich condition that occurs when the engine goes too lean - ask Prolene :-).

There was another poster here that saw his gains from a fuel pressure change diminish over time. Forgot who he was though.

I've built a couple of NA Hondas that, with no fuel mods (stock injectors, regulators, etc.) saw gains of 35%. The only way that will happen is if the ECU is seeing the airflow gains (by looking at mixture) and adding extra fuel to compensate under WOT.

Schatten, additional airflow means that, until the ECU adjusts, you're injecting the same fuel for more air, hence a leaner mixture. Remember, our ECU only reads air pressure, engine speed and throttle position to determine airflow. With flow mods, the same air pressure means more airflow, so the ECU has to adjust the fuel trim numbers. Until it does, the mixture is leaner than what is expected.

UL

Pixsurguy

Just want to say a hearty THANK YOU for the genuinely helpful posts. I'm less ignorant than before.

John Nader