PE Tables and WOT Threshold

[MasterG]

Trying to understand how this works. The FA Power Enrich vs Aircharge vs RPM table represents the desired air/fuel mixture at a given cylinder aircharge and engine RPM. The ECM takes these values and determines the appropriate injector duty cycle to deliver that desired air/fuel ratio. But since this is "open loop" the ECM isn't able to correct the final result. In other words, the computer thinks its delivering 12 AFR, but the measured result on the wideband might be 12.5 AFR.

Am I correct so far?

So part one of my quesiton is about modifying this table. I know at a given aircharge/rpm, the computer is commanding something like 11.5 AFR, but I'm actually measuring 12.5. Now if I want to make it 12, I could just tell the computer to command say 11.0 and then I might end up measuring 12. Maybe that works, but it's really saying that something else is out of calibration. I really need to be telling the computer that it needs to inject more fuel in order to get to that desired ratio as opposed to just faking it, right?

Is there another table I should be tweaking instead?

And my second question is about the setting "WOT Pedal Thresh" which is currently set to 3.1V. I've been monitoring my accel. pedal voltage at 4.57V during WOT. Is this threshold just telling the computer when to switch from normal closed loop to open loop power enrichment? I've also noticed that at wide open throttle, the accelerator pedal position percentage is only about 92%, throttle position 86%, and commanded throttle 76%. Shouldn't these all be at 100%?

[Jay@HAP]

What vehicle are you working on? Are you tuning with NN on or in VE? If you are tuning with the NN on you will change your InjPW vs Fuel Mass tables. If you are doing VE you will set your WOT FA and and adjust the VE accordingly. It's no different than a GM when you set the PE ratio then adjust the VE and/or MAF to get your desired fueling.

WOT Pedal is at what voltage the PCM goes into WOT. The lower the voltage the faster it will got into WOT fueling.

[MasterG]

It's a 2012 Charger SRT, and I have the NN turned on. This is the first time I've tuned anything so I'm figuring things out as I go.

Sounds like step 1 then is recalibrating injpw vs fuel mass so that desired FA matches up with measured FA. Step 2 is adjusting the FA power enrich vs aircharge vs rpm table to get the FA ratio that I actually want? And then once fueling is squared away, I can start messing with timing.

Someone suggested I create a few tunes at different AFRs and then go get on a dyno to see which tune makes the most power. In theory, once I've recalibrated the injpw table, I should be able to easily crank out a few different options just by messing with desired FA, right?

Thanks for the input.

[tbrtuning]

Is the car stock? If you go to a dyno just to test WOT fueling it really doesn't make a difference if it hits what you're targeting or not (flame on everyone that thinks everything has to be perfectly matched). You will test different FA and just go with what works best at each RPM area and it's as simple as that. If it's always 0.03 lean of what you command it isn't that important... You will just be sticking with what makes the most power.

[MasterG]

Mods are cold air intake, ported throttle body, long tubes, high flow cats, and corsa exhaust. I have seen changes by modifying the commanded FA, but when I'm commanding 11.5, I'm actually seeing around 12.5. It just kind of bugs me that things don't line up, but I guess it's just the final number that matters.

[Hemituna]

With NN on (non hellcat), you can adjust the fuel mass vs PW to get the actual FA close to commanded.
So then if you later change the PE numbers, the delivered fuel will be pretty much correct.

[MasterG]

Cool. I think I will start there then. This project is a learning exercise more than anything. I might as well take the time to learn how all of the different tables affect the actual performance.

[MasterG]

WOT Pedal is at what voltage the PCM goes into WOT. The lower the voltage the faster it will got into WOT fueling.

Following up on this comment. I noticed in my custom tune that the tuner dropped the OEM threshold from I think 3.4V to 3.0V so power enrichment starts sooner. What could be some of the reasons for doing so? Are we just trying to prevent the engine from briefly leaning out and stumbling when the throttle is opened quickly? Would there ever be a reason to increase the threshold so power enrichment turns on even later (like 4.0V)? Would you ever approach the other extreme (like 1.0V)?

[Jay@HAP]

Following up on this comment. I noticed in my custom tune that the tuner dropped the OEM threshold from I think 3.4V to 3.0V so power enrichment starts sooner. What could be some of the reasons for doing so? Are we just trying to prevent the engine from briefly leaning out and stumbling when the throttle is opened quickly? Would there ever be a reason to increase the threshold so power enrichment turns on even later (like 4.0V)? Would you ever approach the other extreme (like 1.0V)?

Under Power Enrich, there should be a FA Incr PID, that's the rate how fast in goes into PE, it's kinda like a PE delay on a GM. From Dodge tunes I've seen they are pretty low. On the Hellcat I did, it had a wicked lean spike when you'd go WOT. Even though the TPS voltage was high enough to put it into PE, and it was commanding the WOT FA, it took a bit for the ECM to actually add enough fuel to get there. I ended up maxing that value out and took care of it.

Personally I wouldn't raise the the WOT voltage. The way I look at it is if you are going WOT and putting a huge load on the engine it's going to be delaying PE.

[Hemituna]

There are a couple of WOT thresholds.
Wot Pedal is when the ETC reaches a voltage (OE is usually 3.4 or 3.5ish) and declares the pedal is at WOT and opens the TB fully.
This overrides any airflow or throttle tables and TB goes to wide open. I usually leave this value alone as lowering it can create a sudden transition to wide open.

WOT PE is the voltage that it goes into open loop and also brings in the PE.
This value can be lowered if you want to start feeding it more fuel earlier in the pedal.
I've had it as low as 1.1-1.2v on a blown pentastar so it would start richening just as it came into boost.

As Jay mentioned, the WOT FA ramp rate is usually fairly lazy, so you can dial this up also.

Following up on this comment. I noticed in my custom tune that the tuner dropped the OEM threshold from I think 3.4V to 3.0V so power enrichment starts sooner. What could be some of the reasons for doing so? Are we just trying to prevent the engine from briefly leaning out and stumbling when the throttle is opened quickly? Would there ever be a reason to increase the threshold so power enrichment turns on even later (like 4.0V)? Would you ever approach the other extreme (like 1.0V)?

[Pector55]

With NN on (non hellcat), you can adjust the fuel mass vs PW to get the actual FA close to commanded.
So then if you later change the PE numbers, the delivered fuel will be pretty much correct.

That's how I do it. With VE tuning, I set both PE tables static at 12.5 and dial in the VE until I'm there. With NN on I did the same. Set those two PE tables to 12.5 and just adjusted the fuel mass until it hit and then worked the PE tables to fine tune where I wanted.

[MasterG]

At idle, cyl 1 fuel mass is hovering around 10 mg. WOT nearing redline and it's peaking around 85 mg. This is what I'm seeing consistently in my logs, and the numbers make sense based on the Pratio, displacement, etc.

What doesn't make sense is the fuel mass vs PW table x-axis values: 1.4, 2.9, 3.5, 4.1, 4.7, 5.3, 6.0, 6.9, 8.5, 11.4, 16.2, 51.1, and 1024. 13 data points to calibrate the fuel injectors and only 3/13 are bound within the normal operating range. I'd really like to rescale the axis to have maybe 4 datapoints below 10 mg and 1 above 90 mg. Then I can tweak the pulse-width at say: 10, 20, 30, 40, 50, 60, 70, 85, and 90.

Does anyone else do this?

[MasterG]

I took the leap and tried it out. HPTuners won't let you add data points so you just have the 14 points to work with. I kept the first and last data points and a few in-between. I made an excel spreadsheet to interpolate the data points I wanted to be able to modify. A comparison of my tables is below.

injpw tables.png

If you take these tables and plot them on the same graph, the curves are almost exactly on top of each other. I went out for a drive with this new table loaded, and I couldn't detect any change in driveability. My AFR readings at WOT were basically unchanged as well.

Now I have a couple of graphs in Scanner that are measuring LTFT and a custom math that calculates % error between commanded AFR and what the wideband is measuring during WOT.

afr ltft.png

I'm going to use these two charts to tweak the new injpw table and hopefully get the error as close to zero as possible. Within 1% would be great.

[MasterG]

Still tweaking the injector PW. I think I've been chasing the fuel trims around too much, so I'm going to let it ride for awhile and then hopefully make one final tweak. No big deal.

For simplicity sake, I've flattened out both of the PE tables to command 12.5. The car is actually commanding 12.64 so my calculated input of .0112 in the table might be slighly off but that's not my big issue.... At wide open throttle pulls, the PCM starts commanding more and more fuel. I'm in 3rd gear, WOT, and commanding 12.64. Then I hit about 5200 RPM and it drops to 12.37. 5400 RPM drops to 11.15. Then a slow increase back to 11.20 up to 5700 RPM before a sharp decrease to 10.32. A slow increase to 10.43 for the shift to 4th at 6200 RPM then steady at 10.45 and finally another sharp drop to 9.36 at 4600 RPM in 4th.

Similar behavior was observed during the second run but not identical so there's got to be some other variable that affecting AFR. Any ideas here? Tune and log are attached.

[Jay@HAP]

I had a 15 Scat Pack Charger do the exact same thing. It ended being something in torque management. I ended up putting everything back to stock. With the TM stuff changed it would go stupid rich up top. I'm sure there are more experienced guys out there that know exactly what caused it.

[Hemituna]

Happens sometimes if you raise up the torque adapts. Seems lots of tuners like to do this.
I have found it can cause some weird behaviours like Jay mentioned and the trans can get funky too, like it sometimes can adapt itself to a bad place
Leave them stock or even try reducing them.

I had a 15 Scat Pack Charger do the exact same thing. It ended being something in torque management. I ended up putting everything back to stock. With the TM stuff changed it would go stupid rich up top. I'm sure there are more experienced guys out there that know exactly what caused it.

[Jay@HAP]

Leave them stock or even try reducing them.

quoted for truth.

[WS6HUMMER]

Happens sometimes if you raise up the torque adapts. Seems lots of tuners like to do this.
I have found it can cause some weird behaviours like Jay mentioned and the trans can get funky too, like it sometimes can adapt itself to a bad place
Leave them stock or even try reducing them.

quoted for truth.

Could they also cause issues with a WOT shift, sorry I know this is not the trans tuning forum but I had to ask.

[MasterG]

Torque management settings were completely stock on this tune, including the adapt values. I'm going to try another tune today.

This time, I've disabled torque management, cut the adapts in half, and set FA Max to .0870 (11.5 AFR). We'll see how she does.

tqmgmt.png

On a side note, I have a tune that was done for this car by a pro (on Diablo CMR). That tune has the adapts maxed you like you said. I don't have a firm understanding of that these values do yet, so I just figured this was another way of cutting off the torque management from kicking in.

[xrelapse13]

With NN on (non hellcat), you can adjust the fuel mass vs PW to get the actual FA close to commanded.
So then if you later change the PE numbers, the delivered fuel will be pretty much correct.

You mention on non hellcat.. Does NN on in Hellcat not working with the fuel mass vs. PW adjustment?