Open loop fueling!

Hi all I'm new to the forum and a bit new to hemi tuning as well. Not new to tuning have done countless Gm and Ford vehicles over the years but this hemi stuff is a bit different.. I'm working with an '07 Jeep Grand Cherokee SRT8 so a NGC4. For the life of me I cannot figure out WHY this thing is commanding the max F/A ratio limit whenever its in OL.. Mind you my VE tables are way outta whack right now as I haven't been able to get any good data on this thing yet cause every time I fire it up it wants to command .103 F/A ratio. I feel like even if the VE tables are garbage it should STILL be commanding a logical F/A ratio?!! Thats kinda the point of doing corrections in the VE tables to pull fueling within a couple %.. I have defined my new injector characteristics and added a little airflow for idle thats about it. I haven't messed with any F/A enrichment tables for startup or PE.. I wish there was just an OL table LOL

Any insight on this would be appreciated!

best to post your tune file and recent data log as well as complete mod list. on a side note with the NGC it is best to dial in VE table first then worry about WOT and PE.

I will post up my tune file/and a datalog a little bit later as they are all on my other computer. Mod list is as follows; 428ci stroker I built for it all forged internals, CNC ported heads, boost cam(running NA right now procharger is coming later), ported 6.1 intake,longtubes/full exhaust, fore fuel system with FIC 650CC injectors, motor is 10.4:1 running on 93 right now

And thats the plan, I need to start driving it around to get some good data, I was just curious as to why it wants to command such a rich F/A ratio in OL right now cause that to me doesnt make sense.. fuel error is fuel error but shouldnt be showing up in commanded?

PE is tabled based only so if injector scaling is off and VE table and PE table not dialed in correctly fueling will be off.

Right, that's the idea to get actual fueling to match commanded fueling.. what i'm saying is the commanded F/A ratio the ECM is targeting right now is .103 which equates to 9.7AFR... So you're saying that if VE tables are wack then commanded fuel is gonna be off? I don't see how that works cause if commanded fueling is off how am i supposed to make corrections to VE and injector scaling.. I suppose i could just turn CL on and log STFT+LTFT to get VE in the ballpark. This hemi stuff is odd i'm used to just driving around in OL and logging actual EQ vs commanded EQ and calculating fuel err from that, so i figured i'd set this up the same way except instead of lambda i'd use Phi.. I guess not lol

i might be wrong but when its in open loop there is no commanded air fuel ratio

its 'open' therefor not using all the sensors

a 07 jeep ngc4 comes with a wide band sensor????

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Originally Posted by LilSick

i might be wrong but when its in open loop there is no commanded air fuel ratio

its 'open' therefor not using all the sensors

a 07 jeep ngc4 comes with a wide band sensor????

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Only Hellcat powered vehicles have factory A/F

In OL fueling is usually based off of an OL fueling table(GM and Ford) in chryslers everything is an F/A adder of stoich, even in OL the ecm still has to calculate how much fuel to inject to hit a target FA ratio it just is ignoring any instantaneous corrections the narrowbands are reporting, so there still should be a somewhat logical value commanded for F/A ratio while in OL as far as i'm concerned.. somebody correct me if i'm wrong about the chrysler stuff. And no it doesnt come with a wideband sensor i welded bungs in to run all the O2s and the wideband at the same time. FA ratio is the inverse of what most are used to which is AFR, which means you can calculate AFR from FA and FA from AFR

can you plz explain your statement about

"everything is a f/a added of stoich" and the "target fa ratio (in OL?)"

In chryslers FA ratio is the fuel to air ratio which is the inverse of air to fuel ratio. Chryslers are a bit different than GM and Ford, in GM and Ford you usually have whats called an OL fueling table or a cold/warmup enrichment table its sometimes called, this table will define the actual commanded AFR while in OL(usually in lambda). In chryslers you have a defined FA stoich ratio which will be something like .0694, this defines stoich FA ratio, if you want to calculate what AFR this is simply invert the equation
(1 / .0694 =14.4AFR) for any type of enrichment in chryslers so warmup enrichment or PE the numbers you see in these tables are ADDERS of FA stoich value. Example- FA stoich=.0694 and lets say youre in PE mode running at a Pratio(pressure ratio) of .7 and engine RPM of 4,000 the lookup from the PE table tells us for that condition it will add .011 FA ratio for enrichment so you take your stoich value and do the math- .0694 + .011 = .0804 FA now convert it to AFR to give you a better understanding of what your commanding fuel wise so 1 / .0804 = 12.4AFR

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Originally Posted by GIRGrant

Hi all I'm new to the forum and a bit new to hemi tuning as well. Not new to tuning have done countless Gm and Ford vehicles over the years but this hemi stuff is a bit different.. I'm working with an '07 Jeep Grand Cherokee SRT8 so a NGC4. For the life of me I cannot figure out WHY this thing is commanding the max F/A ratio limit whenever its in OL.. Mind you my VE tables are way outta whack right now as I haven't been able to get any good data on this thing yet cause every time I fire it up it wants to command .103 F/A ratio. I feel like even if the VE tables are garbage it should STILL be commanding a logical F/A ratio?!! Thats kinda the point of doing corrections in the VE tables to pull fueling within a couple %.. I have defined my new injector characteristics and added a little airflow for idle thats about it. I haven't messed with any F/A enrichment tables for startup or PE.. I wish there was just an OL table LOL

Any insight on this would be appreciated!

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I fixed this issue last night... if anyone runs into a weird problem with their NGC chrylser commanding max enrichment at idle in OL and CL will not activate THIS IS YOUR PROBLEM; go into your scanner and connect to the vehicle and then read your DTC codes stored... this issue is caused by a PCM code that when stored causes the PCM to go into a limp mode and doing so it will start commanding max enrichment and staying in OL, the code was "Lost communication with PCM" I can't remember the actual diag code.. I will update later with code. Clear this code and your PCM will properly operate again!!! No more 9.5AFR!!

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Originally Posted by LilSick

can you plz explain your statement about

"everything is a f/a added of stoich" and the "target fa ratio (in OL?)"

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The Pe table can be fine tuned if you do the work, let’s say you have. 2nd stage NOS that hits at 4500rpms @ .90Pratio .we want a 10.5afr at that point in the run. the stoich value is set to .0696, we map the Pe table to what we want rpm@Pratio set the value to .0256 in that cell and a few higher depending on duration and other factors. You can go from 12.3 AFR to 10.5 back to 12.3 if you write the table correctly. I have hillclimb guy who as the course he runs gets higher in elevation, the tune uses different areas of the table, we lean at one part go fat at others.

i thought he was talking about start up?

was he talking about wot ?

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Originally Posted by GIRGrant

I fixed this issue last night... if anyone runs into a weird problem with their NGC chrylser commanding max enrichment at idle in OL and CL will not activate THIS IS YOUR PROBLEM; go into your scanner and connect to the vehicle and then read your DTC codes stored... this issue is caused by a PCM code that when stored causes the PCM to go into a limp mode and doing so it will start commanding max enrichment and staying in OL, the code was "Lost communication with PCM" I can't remember the actual diag code.. I will update later with code. Clear this code and your PCM will properly operate again!!! No more 9.5AFR!!

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That's good info; I hadn't yet run into that problem but good to know what happens - thanks!

Tuning speed density: in closed loop, zero out the fuel trims by adjusting the VE tables. In open loop, create a "fuel trim" percentage number by comparing the commanded AFR to a wide band reading: (CAFR-WBAFR)/CAFR. Use that error to also adjust the VE tables. This works in all open loop situations - WOT or even when in catalytic overtemp. After the VE tables are dialed in, you should be able to command whatever additional FA you want at WOT using the PE tables and she should hit them accurately.

The commanded AFR channel data is a sum of the FA from the PE table (whichever one the PCM is pulling from) when in WOT, along with the calculated stoich FA using the VE table values.

Just make sure the rest of the tune is as accurate as you can get it before dialing in the VE tables, otherwise you'll have some chasing the tail: FI tables, the fuel mass multiplier tables like fuel pressure and temp tables, torque-to-aircharge and its inverse, the aircharge-to-torque tables, etc...

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Originally Posted by rockystock

That's good info; I hadn't yet run into that problem but good to know what happens - thanks!

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No problem! I couldn't find any info on that topic and it was driving me crazy, hopefully it helps someone out lol

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Originally Posted by spoolboy

Rockystock, can you explain how to dial in the aircharge to torque and torque to aircharge tables?

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I'm not aware of any straightforward way to tune those tables. The best approach I can see is to use the tables from a stock tune with an engine that most closely approximates the engine being tuned. For example - I copied the stock 2016 392 tables into my older NGC4 PCM (that never ran 392 from the factory) and haven't modified them because the engine is mostly stock (mild cam and 5-angle valve job on Apache heads from a racing shop). It seems to me that any airflow differences from stock should simply put the engine on different cells in the table; the basic structure of the engine is unchanged. I suspect a significant bore & stroke (for example), or maybe a change in CR might call for a new set of Tq-Aircharge / Aircharge-Tq tables...

These Lovley Tables?

Torque/Airflow Offset:
Torque/Airflow Factor:

These tables deal more with variance in air flow than anything else. As the OS systems evolved these tables expanded to deal with the changing architecture and emission needs.
Look at the 04 NGC tables vs the Gpec tables, simplistic vs Cazy as phuck

When you log TAF(Total Airflow) you’ll notice during W.O.T events the Chart Vs Time “line” looks like a saw blade, the smoother we can make that line the more average “power” we can make, reality is Intake manifold air boundaries issues, Intake reversion, Throttle body flutter all influence Airflow , which makes it imposable to smooth out that line, Now WOT Single plane HIGH….I MEAN HIGH rpm that line looks like it’s a straight edge.

The DCX way of thinking is Airflow…….. Everything revolves around Airflow.
X-amount of Air + Fuel +/- Spark = Tq, which is requested by accelerator pedal (APPSv) , TPSv controls delivery of Tq.

Speaking NGCX systems here , for any 5.7 Pre-Eagle Table 44296 is set to 350G/s while 6.1s are set to 410G/s , why those #s , Well they are based on Hp capability for their respective Head flow#s (yes I said HP not Tq) pre-eagle 5.7s are good for 250CFM @.600 and 6.1s are good for 300CFM @ .600 (on a 28Hg bench) ,
350/.72=486Hp
410/.72=569hp
*Eagle 5.7 is 380G/s =528hp

Other manufacturers and people use .80-.86G/s = 1hp .

If we look at the 5.7(345CI) It’s well known that a good thought out 340-350Ci engine running at real world VE of 80 to 85% will make 480ish HP, between 6500-7k RPMs, that’s why 350G/s was chosen, 486Hp is 1.40 Hp/Ci, easily attainable with 250CFM@ .600 lift

Math is.
[commanded torque (Nm) / Torque/Airflow Factor (Nm/g/sec)] - Torque/Airflow Offset (Nm)
Example:
(04 ram I was working on few weeks back.,)
For 1733RPM, we look at 1532RPM Cell, =7.3200 and 1792RPM Cell = 6.36, Interpolate #s for 1733rpm = 6.58125.
105 Ftlbs = 142.36 Nm, airflow at .50 TPS =34.75G/s airflow at .56 TPS = 41.75g/s TPSv for this given log was .5471V at 1733rpms TAF was 36.1G/s , it was -1.4 LTFT B1 , - 1.9LTFT B2, -1* spark retard actual spark value is 20* for this RPM and MAP area.
142.36/7.3200-(-11.2699) = 30.72G/s
142.36/6.3600-(-11.2699) = 33.65G/s
142.36/6.5812-(-11.2699) = 32.90G/s
All 3 results were below Air Flow value minimum for .50V.
Tq/Airflow offset is 11.2699 for the 04 OS , we add ? of the value to 32.90G/s we get 38.53G/s with is over the actual 36.10G/s the engine is actually flowing at this “snippet” of the log.

Now when you figure out the math for the TQ request from APPS , it’s 140.85 Nm(103.89FTlbs) and we are exceeding it with 142.36Nm(105Ftlbs) which is why there’s a -1 degree spark reduction while the Knock sensor is barely over .6v


Offset" table is a g/sec offset not a torque offset.
Once you have a grasp on how this works, the Loss and Tq reduction tables become easier to tune.

1532RPM,1792 RPM values come from the TQ/Airflow table for a stock 04 5.7