Long & Short term Trims and Corrections under high load areas

Hi, I’ve been ‘tuning’ for around 10 years on a number of different systems and cars. My weopon of choice (and favourite) is MaxxEcu’s Race ECU on my 2004 Evo 8 MR.

As time has creeped on, the ECUs available to us have better and better Closed Loop fuel control along with the all important Saftey Strategies etc etc.

My first stand alone Engine Management system was the Megasquirt assemble yourself kit that was actually very successful, I honed my soldering skills, sensor knowledge & scaling, it even taught me 90% of my computer knowledge - i remember struggling to navigate the basic functions of my laptop!

Anyway, I’d like to start a discussion on fuel trims and general fuel control loops. Like im

sure many of us have, the majority of my tuning has been on the road with the occasional hire of a steady state dyno (what a pleasure that is!) This of course was only possible with data logs and a wideband lambda sensor along with many many hours of patience. Armed with the experience & knowledge I have gained over my 10 plus years I start out with a base map that is fairly close to my particular setup and then set about roughing in my VE tables and onto dialling them in to the best of my ability to acheive decent power but most of all GOOD drivability/road manners and if I’m lucky maybe even ‘better’ fuel economy at light load, once i get things to where I’m somewhat happy and with a second opinion of someone who has been tuning for longer than I’ve been alive! I like to get my fuel to be within 5% plus or minus of my target, the main reason I chose 5% is simply because that’s what I’ve observed from factory cars (I’ve been a mechanic for 26 years) so the furthest I’ll allow myself to be out by is that very 5% although I’ll only allow it upto around 0.5 bar. Anything further up than that I aim to be a bit tighter.

Once my Short term trims are dialled in I will then activate ‘Fuel Adaption’ (I guess this is Maxxecus version of the Long Term trims) and cover as many miles as I can with varying RPM and loads whilst keeping % per second regulations as tight as possible so that I will only see very small fuel corrections over a fairly long time. After that if I start to see any large changes then I treat that as a heads up to any potential issues with my car, those along with safety strategies/warnings give me some sort of ability to sleep at night!!

At high boost of around 1.5 Bar I don’t allow the ECU to make any changes to fuelling, as good as the sensors are these days, I just don’t fully trust a £100 sensor to be in full control of my engine under power, I log my runs then look at my target, actual and the differences in lambda reading, if anything I will allow positive changes but NO negative changes!….I actually run 2 Wideband sensors but not Pre/Post Cat like factory cars, I have them fitted within an inch or so of eachother so that they are both sampling exhaust gas in the same section of pipe, it’s probably laughable if not overkill but with these and a fairly tight control authority I’ve learned to have faith in my overall setup and so far touch wood to date I haven’t broken or melted anything, either that or I’m just not trying hard enough! I’m a firm believer of putting a fresh plug in and reading after a hard pull and other similar tricks, until I know better or break something bad enough I’m just going to keep going, how else do you learn these things, eh?

What are other people’s approach to this and how much do you allow the closed loop to be in charge of? And under heavy load do you let the closed loop catch any differences plus or minus?

Feel free to criticise my method

I don't like using closed loop mode on modified engines at all apart from stoich zone for better emission control so I disable it everywhere above -0.1 Bar (0.9Bar absolute pressure) pressure in intake manifold. The reason being is that I always ask drivers/pilots to keep an eye on lambda gauge readings all the times. Once you get used to it you know exactly what AFR is appropriate for different engine loads and you will immediately notice if that AFR number is different than usual indicating something wrong. I personally find it better than ECU using closed loop mode and covering for a problem instead of me mechanicaly fixing it - intake system air leak, for instance. It can be a problem too if you get air leak during your run but I believe it's my responsibility to ensure car's integrity before event without relying on ECU...