Notes on injector / maf scalining using full time open loop

[mad_sb]

Greetings all.

As anyone who has spent some time poking at our factory rom images knows, there are a number of
tables that affect fueling and load calculations including but not limited too:

• maf sensor scaling
• GDI Pressure Multiplier A & B
• Injector Flow Scaling
• Closed loop Target Compensation A & B (Load)
• Engine Load Compensation (Manifold Pressure)

I have always wanted to zero out the compensation tables, especially the Engine Load Comp table, to see what the affect would be on the over all tune. I speculated it would help smooth out the fueling. I finally got around to forcing full time open loop mode, zeroing out the compensations, and re tuning my injector and maf scalings.

Reasons why you would want / need to do this include:

• replacing your port injectors
• replacing your fuel pump
• tuning for E85
• tuning for boost
• tuning for new intake
• adjusting your existing tune for a change in intakes or any of the above
• Adjusting tip-in settings (keeps fuel trims from affecting tip-in)

A couple of quick notes about forcing open loop:

1. forces port injector only idle, most of the time anyway.. in 3 days of logging i only saw it flip over to DI idle 1 time
2. you have NO fuel trims.. be very careful if your current tune has large fuel trims!

How to Force Full Time Open Loop:

1. Open your Fuel Map
2. Select all cells that are 14.7 and set them to 14.6
3. Set your Minimum Active Primary Open Loop Enrichment to 14.7
4. Set your CL to OL Delay timers to Zero
5. Save and Flash rom
6. Make sure your logger is setup to log commanded AFR as well as measured AFR

A Note about Closed Loop Fueling Target Compensation A & B
Independent of closed vs open loop modes, setting these tables to 14.7 will disable long term fuel trims / AFR Learning. It Seems these tables set the rich boundary for closed loop operation. So, while in closed loop the target afr will fluctuate between the Fuel map target afr and the target compensation map afr. From what i have read, this floating from rich to lean stoich points helps the cat do it's job, which i'm not too concerned about. It seems you cannot set these tables leaner than 14.7, nor can you set the main fuel map leaner than 14.7 (tried it once, saved and re opened the rom to find the call defaulted to full rich).

Ok, so now what?
Now it's all about logging. At this point you need to start logging the actual AFR vs the commanded AFR so that you can calculate (if you logger doesn't do it for you) the AFR Error, that is how far your actual afr is from your fuel map target afr. If you use the simple equation (AFR_Error = (Actual_AFR)/(Target AFR)) you end up with a scaling factor you can use to adjust your maf scale, injector scale (both port and direct) etc.

Used in conjunction with the GDI / Port ratio tables, you can force full time port or full time direct fueling to dial each in separate from each other. The exception is pure idle mode, which will be 100% port the majority of the time while you are in open loop, though i have seen it flip over to DI idle once in the past few days..

My Observations:

I was shocked at how much smoother my car runs after zeroing out the manifold pressure load comp table and how much less variation there is in fueling errors. I have been able to tweak the port and direct scaling tables to the point that i can run full time open loop all day long with zero issues, the car actually runs better than it ever has running full time OL with just a few tweaks to the scaling. I did not need to mess with Maf as I just did that not long ago, but i made the minimal changes needed to get my load back where it was tuned for on the dyno last time after a change to my intake setup.

I also was able to test out using a rich "stoich" target on E85. I had read on romraider that lots of people see best mpg with a stoich target of 14.2 on E85. I can confirm it requires noticeably less throttle angle to maintain speed on flat ground and inclines with 14.2 afr than 14.6 - 14.7 and leaner.

It is possible to re-calibrate the front 02 so that the ecu will actually target 14.2 rather than 14.7 but I think it may also be possible to use a combination of the main fuel map, closed loop target maps, and Minimum Active Primary Open Loop Enrichment to target richer AFR's for high E content fuels. I will test this next and report back.

Attaching a few screen shots of visualizing the data in various ways, as well as the changes i made to GDI Pressure Multiplier A & B and GDI Pressure Target B and how my fuel map looks during these tests:

[Calum]

Interesting. do you plan to keep it OL or is this a step to understanding more so you can tune the CL? Do you think you'll be able to get rid of the tip in knock we all have?

[mad_sb]

Originally Posted by Calum

Interesting. do you plan to keep it OL or is this a step to understanding more so you can tune the CL? Do you think you'll be able to get rid of the tip in knock we all have?

Well, At some point i will turn the short term trims back on but i do plan on trying to target 14.2 ish for closed loop on ethanol. Depends if i can get the closed loop target tables to act the way i want.

I would highly suggest anyone that is working on re-scaling the maf and or injectors go ahead and zero out Engine Load Compensation (MP) and Primary Open Loop Fueling Additive before you start logging for corrections... otherwise your fighting against correction tables that were built off the stock tuning, intake, engine, and exhaust configurations. Once you get your scaling dialed in as close as you can, then you can use the compensation tables for the last bit of fine tuning.

To be honest, i have not seen much tip-in knock at all but i am still NA and running on E90 100% of the time.

[Calum]

Originally Posted by mad_sb

Well, At some point i will turn the short term trims back on but i do plan on trying to target 14.2 ish for closed loop on ethanol. Depends if i can get the closed loop target tables to act the way i want.

I would highly suggest anyone that is working on re-scaling the maf and or injectors go ahead and zero out Engine Load Compensation (MP) and Primary Open Loop Fueling Additive before you start logging for corrections... otherwise your fighting against correction tables that were built off the stock tuning, intake, engine, and exhaust configurations. Once you get your scaling dialed in as close as you can, then you can use the compensation tables for the last bit of fine tuning.

To be honest, i have not seen much tip-in knock at all but i am still NA and running on E90 100% of the time.

Grab some 91, I bet you'll see it then.

Amazing work man, thanks for sharing.

Sent from my GT-S7560M using Tapatalk

[mad_sb]

Originally Posted by Calum

Grab some 91, I bet you'll see it then.

Amazing work man, thanks for sharing.

Sent from my GT-S7560M using Tapatalk

Yeah, I did get it some when i was on pump gas, but i was able to tune most of it out with cam timing, getting control of the closed to open loop transition, and ignition timing.

I did notice when switching over / front pipe combos around the past couple weeks that a pipe that hits the cross-member or sway bar will induce false knock. Not a big surprise i guess.

I'd be curious to see if someone having the tip-in knock could seriously reduce it by taking this approach to get fueling and tip-in enrichment dialed in then switching back to regular OL / CL mode.

[jamesm]

Originally Posted by mad_sb

Yeah, I did get it some when i was on pump gas, but i was able to tune most of it out with cam timing, getting control of the closed to open loop transition, and ignition timing.

I did notice when switching over / front pipe combos around the past couple weeks that a pipe that hits the cross-member or sway bar will induce false knock. Not a big surprise i guess.

I'd be curious to see if someone having the tip-in knock could seriously reduce it by taking this approach to get fueling and tip-in enrichment dialed in then switching back to regular OL / CL mode.

I've got tip-in tuning nailed and <1% fueling error across the board. I still get tip in -1s occasionally, though not as bad as before.

Thanks for the write up . I actually find using trims to be a much faster way of dialing in closed loop fueling, but it's great to see other approaches detailed.

[Kodename47]

Finally got round to fully digesting while looking through the tables, I think I've found the right ones on ECUtek.

Originally Posted by mad_sb

I have always wanted to zero out the compensation tables, especially the Engine Load Comp table, to see what the affect would be on the over all tune. I speculated it would help smooth out the fueling.

I was shocked at how much smoother my car runs after zeroing out the manifold pressure load comp table and how much less variation there is in fueling errors.

How do you mean zeroing out the MAP comp table? What's the advantage of this? I'm running a S/C so putting 0 into this table surely can't be advantageous?

I think I've sorted out the MAF scaling, I need to confirm this when I get a chance to flash the maps. I assume tip-in enrichment is just the throttle delta fuel comp tables?

Originally Posted by jamesm

I've got tip-in tuning nailed and <1% fueling error across the board.

What do you class as fuelling errors? Just the difference between target and resultant AFR?

I've been reading on NASIOC/Romraider on various threads about MAF scaling etc, there's mention about the AFR learn values, are these separate from the LT/STFT's and how and when do they have an effect?

[jamesm]

Originally Posted by Kodename47

Finally got round to fully digesting while looking through the tables, I think I've found the right ones on ECUtek.

How do you mean zeroing out the MAP comp table? What's the advantage of this? I'm running a S/C so putting 0 into this table surely can't be advantageous?

I think I've sorted out the MAF scaling, I need to confirm this when I get a chance to flash the maps. I assume tip-in enrichment is just the throttle delta fuel comp tables?

What do you class as fuelling errors? Just the difference between target and resultant AFR?

I've been reading on NASIOC/Romraider on various threads about MAF scaling etc, there's mention about the AFR learn values, are these separate from the LT/STFT's and how and when do they have an effect?

i mean calculated fueling error across the maf range, as per the screencast i made on the topic. basically you sum the total fueling error (stft and ltft), plot against mafv, and plot the mean and mode.

fwiw everything you'll read on romraider forums about maf scaling is completely wrong for the 86, as it doesn't account for the interoperation of two independent fuel systems (port and di). i chased my tail for months trying to follow their lead before i figured out process separation.

[mad_sb]

Originally Posted by Kodename47

Finally got round to fully digesting while looking through the tables, I think I've found the right ones on ECUtek.

How do you mean zeroing out the MAP comp table? What's the advantage of this? I'm running a S/C so putting 0 into this table surely can't be advantageous?

I think I've sorted out the MAF scaling, I need to confirm this when I get a chance to flash the maps. I assume tip-in enrichment is just the throttle delta fuel comp tables?

What do you class as fuelling errors? Just the difference between target and resultant AFR?

I'm not sure how to explain why zeroing out the map comp table is beneficial... What that table does is apply the table value as a load calc scalar value. It compensates the calculated load based on rpm and manifold pressure. If you look at the values in teh stock table they are all over the place and can make it more difficult to dial in your maf / di / port scaling as a result.

In general, before you tackle maf and or injector scaling, it is best to reset as many compensation tables as you can before you being.

As JamesM said, this is not like a typical car when it comes to injector / maf scaling because of the hybrid fuel system. You have to address each system on it's own then both together. Before touching the maf curve, I would zero out comps, force direct only mode, log and adjust over all DI scale (move the whole table by the same percentage) then force port only mode and do the same, then go back to hybrid mode (because stock port injectors are not big enough to rev it out in port only mode) and adjust maf scaling.

[mad_sb]

Originally Posted by vgi

how about this one: http://www.romraider.com/forum/viewt...02e4cb6dc3d9f8
for open loop scaling, you have a primary open loop fueling table with target values and you can log actual afr and then calculate the AFR error (Kodename47 mentioned it above).
using this method you shouldn't care about the 2 different (port/di)

It's not the method that is flawed it is the fact that you are leaving out the variances between the fuel systems. Above will work fine if you lock in one mode or the other (100% port or 100% DI).

The attached is an example of what i am talking about... columns are fuel system mode, rows are maf V, data is the afr error. Mode 1 is port only, 2 Direct Only, 3 is combined. If you don't separate the system modes you will make a mess of your scaling. Also note, the reason for the high error on port is simply decel mode (throttle andle 0 and injectors shut off), and admittedly this is one area where using the sum of fuel trims works better than AFR error.

[mad_sb]

Originally Posted by jamesm

i mean calculated fueling error across the maf range, as per the screencast i made on the topic. basically you sum the total fueling error (stft and ltft), plot against mafv, and plot the mean and mode....

AFR error is easier as it is simply actual afr / target afr and gives you your final scalar number straight away

[jamesm]

Originally Posted by mad_sb

AFR error is easier as it is simply actual afr / target afr and gives you your final scalar number straight away

yeah but i find that it's better to see the 'whole picture' as there's latecy and all that to worry about as well. it's not very often that you just have a straight line of error across the whole maf range when tuning large injectors.

[jamesm]

Originally Posted by mad_sb

I'm not sure how to explain why zeroing out the map comp table is beneficial... What that table does is apply the table value as a load calc scalar value. It compensates the calculated load based on rpm and manifold pressure. If you look at the values in teh stock table they are all over the place and can make it more difficult to dial in your maf / di / port scaling as a result.

In general, before you tackle maf and or injector scaling, it is best to reset as many compensation tables as you can before you being.

As JamesM said, this is not like a typical car when it comes to injector / maf scaling because of the hybrid fuel system. You have to address each system on it's own then both together. Before touching the maf curve, I would zero out comps, force direct only mode, log and adjust over all DI scale (move the whole table by the same percentage) then force port only mode and do the same, then go back to hybrid mode (because stock port injectors are not big enough to rev it out in port only mode) and adjust maf scaling.

the main difference between that and what i do is that i don't mess with the di stuff. my theory is 'didn't change it, don't touch it.' so i first log DI only, scaled the maf just generally up and down against that (always tuning larger maf housings lol), then log port only and tune latency and scaler from that (with a now known-good maf as far as the scaling for size), then combine and fine tune the maf.

you can get fueling error across the board within 3% in a couple hours this way (given a decently designed maf tube). i'm not sure it's the best way, but it works for me.

[jamesm]

Originally Posted by vgi

well yes, but i thought that was the whole point - both, di and port work as a single system. the ratio between them only determines which one works harder at what time but at the end the result is 100% - total amount of fuel in the cylinder. what are those variances i should watch out for?
i mean, if i need a gallon of milk, do i care i 1 cow gets milked or 2?

also, that maf scaling is done WOT data only

because the ratio between them changes, and the amount of fueling error for each is different (until you fix it). the trims aren't aware of the ratio, so if you've got 20% port fueling error and -10% di fueling error in a given range and you pass in an rpm cell from using 50% port to 0% port, you can imagine what happens .

technically they only both need to be wrong the same amount and in the same direction, but ideally you just want them both right.

note that most of this only applies when tuning larger injectors and maf housings. if you don't change you're injectors, you don't have that variable to worry about as much.