Country Boy

iTrader: (24)

Ive thought about using 100% MAF at times, but was worried about low speed problems with big cams and such. Also worried about reversion.

If one scews IFR, then it messes with IDC, right?

SSpdDmon

iTrader: (10)

If you screw with IFR, is it truly wrong? IDK. I go back and forth some days. Rumor has it that the guy who tuned my dad's car used to work for GM on the PCM's (according to some of the Vette guys who met him). If that's true, I'd have a hard time taking credibility away from him and his 100% MAF/IFR approach.

As for me, I'm going to stick with tweaking the MAF curve (with the right IFR for my injectors) for the next couple of weeks to see just how close I can get things. There's still an AFR variance with IAT's. I'll probably need to move to COS#5 to deal with that. But, at least now I can keep things a little more consistent when logging with the relocated IAT.

On a side note, it was raining pretty good this morning and I was behind quite a few rooster tails on the highway. I popped the hood when I got to work and there wasn't a drop of water near the IAT - bone dry. So, it looks like I picked a good spot.

Frost

iTrader: (45)

I've tried setting the MAF bias VERY low like said the first post but it's given me a fit with bigger cams. I hate to give away methodology and what-not, but for N/A, I move the MAF bias down to 1800-2200 and tune the VE up to about 2K and calibrate the MAF.

Don - what I don't understand is, if you are working the MAF anyway, why not build in the numbers that drive the trims negative there rather than IFR?

SSpdDmon

iTrader: (10)

Because of the theory that GM did extensive research on MAF flow meaning the MAF table is right and doesn't need to be touched. Problem is, I don't know many people running a factory lid (baffles and all) with their H/C setup. The next question is, if the curve is so accurate in factory form, why not put the factory intake assembly back on the car. Then, you'd have a safe, consistent setup at the expense of 10hp - not to mention another element of stealth.

LS1curious

Justs a side note to this. I tested the Many baffle and lid combinations out there. the SLP lid with the smooth bellows produced the best curve fit to factory the least amount of signal noise. I did test for HP. With and without lid. Made no difference on engine upto 400ci and well over 550 flywhl hp. This was all done using the plastic 85mm mafs in there various configuarations. the metal 3 pins where within 2-3hp of the plastics on engine up to 347ci at 500flywheel the error range of the dyno.

SSpdDmon

iTrader: (10)

With my SLP MAF and SLP Lid, the AFR is off significantly (-9%~11%) at different points along the curve. Currently, it's set as follows:

Idle Frequencies: Had to add ~3% to keep AFR at 14.5~15:1.
Low TPS (3250~4250Hz): Had to pull 6~8% out of the curve to keep AFR at 14.5~15:1 or it would run too rich.
Moderate TPS (4500~6500Hz): Varies from -4%~4% to maintain stoich AFR.
Heavy/WOT TPS (>6500Hz): Varies from 4%~11% to get commanded AFR to equal WBO2 AFR.

That's a 20% variance! Any reason why?

NicD

iTrader: (7)

I have seen this repeated more than once and it's not correct. Injector duty cycle is calculated using injector pulsewidth and RPM. The IFR table has nothing to do with this calculation.

RedHardSupra

iTrader: (1)

yes, but ultimately the amount of fuel dumped (fuelmass) is IPW*IFR, so people who screw with IFR effectively screw with IPW, so the IDC will change. that's why i'm so **** about getting the IFR absolutely as close to reality as possible. without real IFR you'll never know how hard your injectors are working, and that might end badly if they're underreporting.

NicD

iTrader: (7)

IFR is irrelevant. Injector duty cycle is calculated with the end result of the fueling, IPW vs RPM. It doesn't matter how it got there and surely not calculated with IPW*IFR. Making a car run with a 12.5 a/f through a WOT run using different methods (like changing IFR, then skewing MAF or PE tables or whatever) doesn't change your duty cycle. I thought this was pretty basic stuff.

RedHardSupra

iTrader: (1)

ok, so what's your theory? just please back it up with more than 'others do it and it works fine'

NicD

iTrader: (7)

I stopped trying to convince people on the internet of things long ago but here is a simple test for you or anybody else for that matter. Grab a car and log the duty cycle over a WOT run. Go back and cut the IFR, MAF, and VE tables in half to give basically the same fueling result. Go make another WOT run. Not to ruin the suprise or anything but it will be the same because it doesn't care about IFR, it only uses the IPW and RPM in the calculation for duty cycle. I don't have a theory, it's a fact that duty cycle is calculated using IPW and RPM. IPW is not a calculated number and neither is RPM, they just are.

SSpdDmon

iTrader: (10)

Marcin, I think he's saying that GM.INJPW1 is purely the amount of time the PCM is commanding, after all of it's fueling calculations, for the injectors to stay open - regardless of what it thinks the IFR is. Assuming that's right, then it's an independent variable. Take that variable along with the given RPM and you have what you need for injector duty cycle.

Formula : IPW*RPM/1200=IDC%

I think we like the PCM to have the right information so we can make it easier to figure things out (i.e. when we're using custom pids) or for future mods, because in theory it should be an easier re-tune.

RedHardSupra

iTrader: (1)

ah yes, if you cut both IFR and MAF/VE tables in half then yes, i thought you're talking about IFR alone since you said IFR is irrelevant.
however, even if IDC will be right, your airmass would be halved too, so all your timing, and any other load based stuff like trans would be wrong.

IFR does matter. it only describes changes in fueling according to MAP changes. if you do a tune only with IFR you basically choose to ignore changes from other factors like temps and RPM. can you honestly tell me that you can tune a car saying that 100kPa MAP will demand the same fueling at 1000RPM and 6000RPM? there's a lot more factors here, that's why VE has both MAP and RPM axis, not just load.

NicD

iTrader: (7)

Why would you need to have a custom injector duty cycle pid when the standard IDC in the scanner is always correct no matter how skewed the program may be?

SSpdDmon

iTrader: (10)

It's a calculated pid in EFI Live. There's no SAE.* or GM.* injector duty cycle pid.

NicD

iTrader: (7)

I never claimed it wouldn't be off in other ways. Obviously other calculations will be off, but I am saying IDC is calculated one way and one way only and it will always be accurate regardless of what you set your IFR to. You disagreed with me and claimed that everybody logging IDC will be wrong if you have the wrong IFR set. This is just wrong information.


I am not even going to respond to this, it's rediculous and I have no idea where this came from.

NicD

iTrader: (7)

I know there is not a real injector duty cycle pid from the computer, that's not what I was getting at. Can you tell us all how the standard calculated IDC pid is calculated in the scanner?

SSpdDmon

iTrader: (10)

Either way, as I stated before, I believe IFR should be set accurately and not used as a tuning table. It's purpose, if I understand correctly, it to tell the PCM how the injectors react to a changing manifold vacuum (think of drinking out of a straw). The more vacuum, the easier they will flow once the window (IPW) opens up. Wasn't this table added due to the absence of a vacuum referenced fuel pressure regulator? That's the purpose it serves IMO.

The PCM should then take the other variables it knows (along with what it knows about injector performance) to calculate fuel delivery. Assuming we can determine the constants around the injector's true performance (true fuel pressure, true injector offset, true flow rate, etc.) for all of the various types of driving, we should be able to eliminate the variables and improve fueling accuracy. The problem is, we don't have that information and all we can do is guess. That's what has me so frustrated...

SSpdDmon

iTrader: (10)

I did in my post above....

IPW*RPM/1200=IDC%

NicD

iTrader: (7)

I am not arguing about whether it's OK or not and what the consequences are from somebody setting the IFR wrong. I personally set the IFR to match the injectors, but if it's set wrong it will not give you the wrong injector duty cycle readings. That is the wrong type of information I see people repeating, thus my posting.