FCar2000TA

iTrader: (7)

I got the MAF table pretty close to done, so I have started looking at what else I can do to fine tune my tune. If I am going to be running a MAF, do I still need to fine tune the VE Table?

AdsoYo

iTrader: (1)

Not if you set the tune to MAF only. Otherwise yes you should calibrate the VE table.

FCar2000TA

iTrader: (7)

I am pretty sure it is all MAF. It needs to be due to significant elevation and temperature changes in the area. How can I verify?

NSFW

Does speed-density generally have problems with elevation and temperature changes with these PCMs? It measures the pressure in the manifold (which is where it matters most because that's forcing air into cylinders) and it measures intake air temperature (which is what matters most because that tells it how dense the air is in the manifold) and with those two things and a VE table I'd expect it to handle elevation and temperature changes just fine...

FCar2000TA

iTrader: (7)

Why is SD better if all of the manufacturers do MAF? It seems like it is the same argument with PD blowers and Procharger. Zero manufacturers use Procharger.

I have zero experience, just going off what I have read, so please educate me.

AdsoYo

iTrader: (1)

In order to run MAF only, go to Engine > Airflow > Dynamic. Then under the Dynamic Airflow column, set "High RPM Disable" to 400 rpm.




Here are my settings for all the cracker, follower, and rolling idle tables. Give these a try and see if it makes a difference.

Darth_V8r

iTrader: (4)

Maf is generally better at steady state stuff like idle, highway cruise, and wot. SD is better at dynamic loads.

SD can generally do steady state better than a maf can do dynamic loads.

The stock pcm generally runs on the maf and jumps over to SD when it senses a dynamic load. Then switches back to maf when it senses it's back to steady state.

The maf can provide for an extra layer of filtering which stabilizes fueling and therefore can help stabilize idle.

SD only will generally result in the engine feeling more responsive at the risk of a loss of stability

This part is a guess, but I'm pretty sure the maf is better for emissions because you directly measure the airflow vs modeling the airflow.

Both systems back each other up. If you lose your maf the car will run in SD. If you lose map sensor, the car will run maf only.

Hope that helps

rpturbo

iTrader: (47)

Fantastic explanation. I would probably say though at the last paragraph, " If you loose your MAF, the car will run in SD, if your tune in SD is pretty close"

I only say that, because I've seen a maf raped enough, if it was unplugged, the car would just die.

FCar2000TA

iTrader: (7)

So, for a daily driver that could see elevation changes of a mile and temperature changes of 60 degrees, would it be better to do one or the other, or both?

NA for the foreseeable future. I only go to the track once or twice a year, if that.

ddnspider

iTrader: (26)

I'd skip the SD unless you want to try and hit the majority of the matrix now and then all over again when booster only twice as many cells then. Just run the MAF and start playing with timing if you haven't already and then idle/tip in.

AdsoYo

iTrader: (1)

Might get a lot of different opinions. I live at 3500-4000ft with a lot of variety in elevation and temps and like running MAF only. However I did still meticulously calibrate the VE table just in case the MAF ever takes a dump.

FCar2000TA

iTrader: (7)

Thanks, Darth. You always explain things well!

NSFW

I haven't got a lot of experience with SD either, but I was under the impression that SD is not rare for factory electronics, and that lots of aftermarket / standalone systems use SD as well.

Subaru uses MAF from the factory, and the cool kids are running SD instead, with modified ECU firmware. Apparently the grass is always greener on the other side.

Funny thing though... a lot of the people using SD on their Subarus are using an open-source project derived from code that I wrote for my own car. But I never actually finished converting my own car to SD. Just too many projects and not enough time. Another guy picked up where I left off and ported it to a bunch of other Subarus, from roughly 2004-2012 or so.

Darth_V8r

iTrader: (4)

This! I personally prefer to dial in the VE, and I do on my own cars and when I tune for friends (because they have the trust level). However, when tuning for a customer - especially over email - the patience is not always there to deal with the car running like crap for five or six writes as you learn it in. In those cases, it's generally easier to go maf-only and the customer gets the instant gratification of the car running better with fewer writes.

It's more of a problem with the more aggressive cams. One additional thing also... As you get more experience tuning, you will find that sometimes you need to idle lean, but this can contribute to a lean tip-in -- when you hit the throttle you go momentarily lean. I find that I can put higher values in the VE table in the right spots and when the car is in blended mode, it senses a sudden change when you mash the throttle, and the VE table can give you a "pump shot" If you log those cells, the trims will tell you it's rich and keep trying to cut fuel.

Anyway, you can file that one away for a rainy day if you ever run into it.

ddnspider

iTrader: (26)

@FCar2000TA How's the drivability with the MAF in that large of a tube? Are you using a honeycomb? What's the engine/cam spec's again? I've reached the MAF frequency limit...AGAIN....on my LS7 in a 4 inch tube and have been curious and going to a 5 inch.

FCar2000TA

iTrader: (7)

It seems to be working fine. I did add the honeycomb to straighten the air flow.

For the tune, I just started off adding 25% across the MAF table, and that actually worked decently. Actually left it like that for a while.

smokeshow

iTrader: (17)

Both MAF and the speed density model have perks and drawbacks. GM stuff has both because the company is not particularly cheap with their hardware. Others, like legacy Chrysler controls (and much of the modern stuff too) uses a calculated MAP based on a throttle body characterization which is backed up by an actual MAP sensor. They are admittedly not as liberal with the money they spend on sensors... The preference of MAF over SD for difficult scenarios like change in elevation or seasonal temperature change is just due to it being easier to measure something than to model it...in this case, mass flow rate. Go up in elevation, baro drops and your volumetric efficiency improves because it has less atmosphere to push against to get the exhaust out of the cylinder. Likewise with temperature changes, its not the IAT that matters but the charge temp itself. Which is affected by the amount of airflow through the engine and the coolant temp, not to mention thermal mass and conductivity of the intake tract and manifold. If you find yourself chasing fuel trims in the afternoon vs the morning...that's likely why. The issue is in the complex temperature model, but its not straightforward to calibrate. I currently can only calculate temp model corrections in MATLAB, as its a first order ODE with a time variant component...the HP Tuners scanner can't do that.

Just thought I'd drop some info on this. Lot of misinfo on youtube and elsewhere...

G Atsma

That is a very good explanation some of the intricacies of the modern ignition/EFI system! Thank you!

smokeshow

iTrader: (17)

Bit of word vomit lol, but hopefully it helps.

NSFW

Do you know if there's any correlation between MAF-vs-SD and NA-vs-FI?

One of the reasons the Subaru folks like to switch to SD is a concern about time lag between airflow at the MAF sensor and airflow into the combustion chambers after large sudden throttle changes, especially with large intercoolers.