VE definition? (cross-platform w/ AEM)
 

Looking at Hustler's thread, he was going on at length about getting the VE table just right and aiming to make a boatload of HP while getting 35mpg cruising at 75-80mph.

I know that VE is Volumetric Efficiency, but all of the documentation I've tried to look up makes it seem like the VE table is what drives the injectors. I have an AEM EMS-4 and our options are fuel in units of time (i.e. - open the injector for X milliseconds at this load vs rpm).

Is it worth it trying to create a VE table for just cross-reference with the MegaSplooge guys, or am I better off just tuning fuel to the AFR target and calling it done?

You cant create a VE table with the EMS4 unfortunately. If you look in the ECU section I have a spreadsheet that will calculate it for you. Yes it really does suck to assume your choice of ecu has exceptionally basic features and it doesnt.

Just go to the fuel table and adjust values so you hit your target AFR numbers, it doesn't matter if we're talking PW or VE, you get the same product in the end.

I adjusted my VE table for 14.7:1 in the cruise cells, let EGO correction take it to 16.1:1 in cruise.

I saw the biggest increase in fuel economy from enrichment tuning to a tedious degree that I doubt few care to explore. There are six tables to dial-in on EAE correction and doing that got me another 4mpg. My theoretical enrichment targets are on the lean-side of the target below 85kpa with TPS only used in downshifting and burnouts.

Hustler the biggest issue with the AEM is that there is a disconnect between the EGO table and the fuel table. Like the values on the target afr ego table dont effect fueling if you have closed loop off. So you cant really do what you describe without tuning the fuel map to 16.1:1 as well.

My AEM EMS: With close loop fuel correction off, I idle at 11:1ish (turn my 4 headlights on, both rad fans, blower, wipers, etc, and the idle gets leaner. Battery volts correction table...well I won't get into that here). My AFR target table is 15.5 and it works great. I like it to be rich and have autotune make it leaner. So you can do what hustler describes.

The closed loop during cruise doesn't work as well. I'm sure it would if I spent the time, but I instead spend the time tuning the PW fuel table so the open loop is where I want it. You would call me lazy.

I tried AEM's autotune, which uses a target AFR table to tune the PW map, and it made some scary changes within a few hundred feet so I turned it off, this was years ago. that too should work well if I took the time to learn how to set the various autotune control settings.

EDIT: I will say that having a VE table would be 'nice', so fueling increases would be easier by just setting a new AFR in the zone(s). But I can add x% more fuel in the PW table zone(s).

Tim that doesnt make me feel any better about what I have to do this weekend. I really should have bought a MS. I have a feeling I'm going to be channeling sammy hagar, what used to take 2 hours now takes all day...

Open loop in MS means essentially 0% EGO authority; I don't understand your comment.

If you have the tune setup correctly your ego targets still have authority because they are part of the fuel calculation. IE if you have your 100kpa line on your car right not set to 13.4 but decide thats a bit too lean you can just change that to 13.2 and you'll have 13.2 afr. If you do that in the aem thats completely tuned in you'll still have 13.4.

Oh, yeah, understood. Its really nice to do that, after the car is tuned.

Yup, it's silly that the AEM doesn't explicitly use a VE table and the AFR target table doesn't affect open-loop fueling.

What you *can* do in the AEM is set up the "boost comp" table to have it rise proportionally with MAP; this will flatten the raw 3D fuel table numbers that you need, so it doesn't change much with MAP. Note that boost comp has units of "%adder", so at 20 kPa, you need to enter "-80".

However the AFR table still doesn't influence the PW calcs. However what this can do that the MS setup can't, is to make open loop fuel be say, richer than the final AFR target. So during a transient you will initially get slightly richer AFR's, then the closed loop fuel will lean it out to the target.

Jason, Want to give your settings for the closed loop variables?

At the AEM class way back when Mitch Peterson recommended using the regular fuel map for the vacuum zones, and the boost comp for any positive pressure zones. Meaning, don't comp anything in vacuum. I forget what he used on the dimenstration shop eclipse for the extra percent per PSI boost, but it was a straight sloping line. And yeah, this definitely flattens out your fuel map, gives you a whole lot more resolution. And the graph view of your map would look odd. I really should try this.

Bah, there's no reason for that, unless you are used to seeing PW numbers in your fuel table, instead of VE.

One other thing I've done is put in an RPM vs VE curve into the RPM fuel comp curves (it's per cylinder, so you have to copy it into all 4). I tweak this, and the boost comp curve, in the early stages of fuel tuning, and leave the main fuel table completely flat.

It is a straight line for mani-referenced FPRs. If you have an atmo-referenced FPR and you want to compensate for its effect on PW, you can generate the boost comp curve in Excel and you will find it will have an upward curve.

You can use Excel to translate your existing fuel table and boost comp curve, to a VE-ish curve.

:eek4dance

I thought I escaped this foolishness when I got away from an ecu that used alpha-n for fueling and was boosted.

The MS doesn't have compensation for mani vs atmo reference, does it?

I'm sure it does. GM ecu's normally do because they often have atmo reference fprs.

I'm not familiar with this RPM fuel comp trim. Is this a AEMtuner thing? I'm still Series 1/AEMPro/Thinkpad 600/Pentium 2.

Flat as in, you fill the entire table with a bit value right in the middle of the range (128)? How do you decide on a MS per Bit value initially?

Are you describing what MegaSquirt calls incorporate AFR?

If so only MS3 does that, and even then it's optional, 99% of the available basemaps don't have it enabled either.

I don't see the massive advantage to it either, once it's tuned it's tuned, shouldn't make any difference whether the AFR targets are used as a part of the fuelling equation or not?

RPM fuel trim is in Series 1.

Flat, as in all 100's, initially.

I choose uS per bit initially that gives me those 100's.
i.e. 100 x us/bit = fuel pulse width I need at 100 kPa.

boost comp curve crosses 0% correction at 100 kPa.

I wasn't clear. Does MS have a checkbox for selecting atmo-ref vs. mani-ref FPR's?

The advantage is ease of tuning.

As was pointed out earlier, if you have an AFR target at some MAP/RPM combo of say 13.5, and you decide you want 13, just change that. Without "incorporate AFR", you would have to add 3.8% to the fuel table entry, *and* change the AFR target too. And then if the 2 get out of whack, you need to address it.