Tuning MAF for Speed Density

[kingtal0n]

Helpful as usual. I pretty much had that covered with the last engine which is currently on the stand for some details like a cam change, different head gaskets, and a new rear seal. I set up the channels, the graphs, the user maths and the charts, including an AFR% table for copy/paste tuning. All that works pretty well.

What I was curious about, was this quote:



It's that last part I'm not clear on. How exactly does it tell you how much fuel to remove or add? It's in different units.

Jim

You did that already. I was referring to the "on" button where you input 13:1 to get the engine started earlier.


So now I am not quite sure what you are asking because you must be talking about something else. Did you see in my picture the a/f units are shown? That chart or graph can be used for "rough tuning" but not fine tuning. Rough tuning because as IAT changes so does A/F ratio, and the IAT sensors tend to heat soak. An issue which I assume you haven't had the pleasure of noticing yet so I am waiting to explain how to get around it in gory detail different ways. Unless you are using Narrowbands , which I Do not recommend, for various reasons. Narrowbands are for letting the computer tune for you, instead of actually tuning the engine yourself properly the way you want. Narrowbands control the a/f ratio like an 'auto tune' feature but that means they are adjusting in your absence, as if you are not truly tuning the engine yourself anymore. That and 14.7 is neither optimal nor ideal for any situation. Slight throttle transitions are 14.3 to 14.5 for response issues. Cruise and idle is 15:1 for clean plugs. 14.7 is basically useless. Also it will tan up the plugs which I don't like to see.

[kingtal0n]

The basic method to tune the engine is first make large gross adjustments to your open loop fuel VE map to get within a fair % margin of the a/f you want to see at each cell. Like in my picture they are pretty damn good.

Once you've done that (a few times in various conditions) you will start to see the numbers skew due to iat and other issues such as heat and voltage issues over time. That requires more rough tuning and logging and correcting the alternative maps of which there are like 20 different maps that play a role in what the VE table does.

From there leave the table rough and work on the PE transition. Set up PE so that it only kicks in when your vehicle is absolutely in need of enrichment, in order to save fuel if economy is a requirement (for me it is, I daily driver). So for me example my PE kicks in like 85KPA+ and perhaps 32% throttle and higher.

However take note my transition PRIOR to PE mode is still richer than 14.7- in fact it is close to 13.0 near 80KPA. So even though I am not using PE I am still getting PE-like enrichment from the VE table. Then, if you are paying close attention you will see a slight "hole" or lean dip in my VE table just approaching 85KPA. This is so the fuel VE Map can transition into PE mode and keep the PE Mode commanded A/F matching actual. In other words, the Pre-PE portion of my VE map is tuned to 14.2 to 13.5's but the commanded a/f for those regions is still 14.7. SO the wideband is saying 13.3 but the computer is commanding 14.7 and its in open loop so the computer makes NO attempt to correct that. This is another reason you don't want narrowbands running, it will prevent you from tuning the VE map properly like a true stand-alone computer where the VE map follows part throttle transitions instead of depending on the PE enrichment mode to do the job, which is very messy and can be confusing because PE mode utilizes several non-common sense approaches such as enrichment ramp in rate which is a number from 0 to 4 and uses very specific throttle, map, and rpm breakpoints for activation... so the criterion is difficult to nail down when all you want is just a slight enrichment at 65-75KPA which can be done quickly and easily in the VE map by avoiding the use of narrowbands and PE mode until absolutely necessary (85KPA+)

[kingtal0n]

Once you've done that with the PE and transition, still rough but close (spend a couple hours then leave it 'rough' and move on) you will need to review the entire tune file for ALL and ANYTHING that has a role in fueling. And I Mean everything. Look at every setting in every window and write down anything you don't understand or know what it does. Try to learn every feature at that point because the LAST THING You want to do is spend 100 hours fine tuning the VE map perfectly only to realize there is some small setting in an obscure window somewhere that completely disrupts and obliterates your entire tuning job. I will as usual give an example from my experience.

somewhere in the ECU there is a thing called CTS/IAT Bias. When I first started tuning I left it alone, like most things. I fully tune my entire VE map thinking what a great job I had done. But then I noticed the IAT or CTS temperature would strongly influence the a/f ratio, say when the engine got a bit hotter than usual or the IAT got heat soaked from sitting in the hot sun after a hard run during traffic. And so forth.

So I went into this BIAS setting thinking, "okay I will adjust slightly to bias the car more towards CTS than IAT and that should fix my IAT heat soaking" or whatever.
And WALAA the entire VE map was suddenly completely off. Wayyy off. It trashed my 20 hours (or whatever) Of tuning efforts in a single blow, just 1 number.

So this was just an example. You need to find ALL those kinds of settings and FINALIZE them before moving on to the FINE tuning stages of the VE map and similar settings. Otherwise you will spend days or months fine tuning a perfect tune and then realize you need some bias or something because of a weird behavior you can't seem to tune around and WHAM all that effort is gone. That is also why we NEVER tune idle and tend to avoid cranking fuel settings until all of these minor settings, global settings, have been dealt with and finalized.

[Jim Blackwood]

I see the A/F ratio.
I have NB sensors installed but STFT and LTFT turned off.

correcting the alternative maps of which there are like 20 different maps that play a role in what the VE table does.

Sure would be nice if someone would list those tables and what they really do. That may be the hardest part of learning to tune this beastie.
Haven't really done anything with PE yet as I'm more familiar with making those adjustments in the VE table. But there's time for that after it is good for gentler driving.

somewhere in the ECU there is a thing called CTS/IAT Bias.

I'll look into this, any tips on how I might know how to set it?

I'll admit I've been using something more of a wholistic approach so I've looked into a lot of areas that it seems most are content to simply not touch and that seems sensible. After all, GM has thousands of man hours in on this. BUT, on the 300 Buick they have exactly zero man hours. Weird as it sounds that kinda makes me the expert? Man, that can't be expected to end well by anyone. Trying to change that here.

BTW, I had an injector burn out and it'll be a week or so before I can install a new one so I may drop out of sight for a few days. I'm going looking for that IAT/CTS bias though. I installed my IAT sensor in a plastic bung in the air filter housing but no doubt it'll still get some heat soak. Not as much as if I'd mounted it in metal but some.

Edit: Closest thing I've found so far is Engine/Oxygen Sensors/Feedback/Closed Loop Enable/ECT vs IAT. Would that be it? I've not touched that but it has 93 in all the cells except -4, -22 and -40 where it's 140. See no need to mess with it.


Jim

[kingtal0n]

nah its somewhere else. I dont have the tuning software on this laptop or I would just show you.

Its labelled as a "bias" feature and there is some kind of warning on it about forced induction setups. It says something like " recommend to disable CTS bias" iirc.

which is what I recommend. I tested it both ways and the coolant temp of my engine would vary too much during the day/night or highway cruise vs highway play, so I completely disabled the CTS portion and just use the IAT alone. As the IAT wanders from heat soak it will screw with the a/f ratio still a little, so my Fix there was to install a variable resistor between the ECU and IAT that I can dial up or down at will. about 500Ohms is a little too small but it works fine. I would suggest 1000OHMS for more control. But nothing over 1000ohms because you might forget you turned it one way or the other.

And the trick to it is, you can program timing adders to take advantage of the variable resistance setting. For example if you are "cool" at 84*F and you know the engine is cool and hasn't been run hard, and the air is cool, and its night time, etc... Then you can twist the knob to add a degree or two of timing whenever you want it. Real time tuning, almost, hah

[Jim Blackwood]

Can't seem to find it. Could be overlooking it I guess, or maybe an earlier version of the software? Anyway I'll not go borrowing trouble if I don't have heat soak problems, and maybe I won't need to mess with it. (Like that has ever worked in the past, yeah.)

Jim