How does the PCM calculate Airflow, and why might it be so all over the place, and only during WOT? During cruise, it's nice and smooth, no valleys/peaks. I see some minor fluctuations in map signal (+/- 2 kpa or so) during WOT, but I don't see minor fluctuations accounting for such massive swings in the total airflow.
Jeep_SRT-8.hpt
Jeep_SRT-8.hpl
Airflow.PNG
Last edited by B00STJUNKY; 07-22-2018 at 09:56 PM.
Your throttle body is fluctuating, causing fluctuations in MAP and airflow. Log your torque source, see why the ECU is shutting the throttle, must be some torque management or torque correlation stepping in.
More info on the Jeep's mods?
I'm seeing very minor fluctuations in TPS%, something I would almost attribute to electrical noise.Originally Posted by 06300CSRT8
Unfortunately I am unable to log torque source (at least last time I tried). I'll check again with the most recent beta.
Jeep is a 2006 WK1 SRT8, NGC3 CAN PCM, currently on stock injectors, NSRT4 2.25 BAR MAP sensor (used to have a procharger), forged 426, Kooks LT headers, Corsa exhaust, 3200 Pro-Torque converter, Paramount S2 valve body.
Im not sure how air flow is calculated but I noticed that your map reading is low for WOT conditions. Normally I see that in the upper 90's to low 100's kpa. I would probably try putting in the stock map sensor and adjusting the tune for it. Does that air flow fluctuation seem to be causing any driveabilty problems?
Minor or not, your throttle body should be pegged and not move more than 0.1 to 0.2% during a WOT pull, unless torque management is kicking in. I would raise your trans side torque limit higher than stock 443lb ft.
I agree with Dito your MAP readings are on the low side, should be closer to 95kpa or so, unless you have a vacuum leak. I would be checking around for some mechanical reason it is reading low, it may lead to figuring out the erratic airflows, as well. I think there is more than one PID for logging airflow, think it might be Aircharge or sonic flow, etc. The one you are logging might be the one that toggles between sensed and calculated map readings and will fluctuate wildly as it does so.
Went out and did some tests. I ended up changing the trans side max torque to 550 lb/ft. Made no difference in the readings. Tried changing the Airflow Max RPM table (which I had to scale down the RPM to accomplish since HP Tuners has the limits set really low for that table at 68 lbs/min, where in stock form, there are values which read above 93 lbs/min), and that made no difference, either.
Finally, I decided to just scale down the Airflow model for the Throttle Body to about 35% of stock airflow numbers. That made the airflow readings trend more steadily, and makes me wonder if it just isn't a resolution error. For example, in the NSRT-4 applications, you can install a 3 bar MAP sensor and properly scale the PCM for it. But once you exceed 255 kPa, the kPa reading then zeroes out, and starts counting back up from zero (so you basically have to take the 255 cap and add it to whatever the final result was from counting back up from zero).
It also makes me question the reasoning behind broadcasting such inaccurate data for the airflow model. We all know I'm not producing much of anything in excess of 500 HP being a low comp build 426, especially at elevation (more on that later in this post). Yet, the Total Airflow PID logs over 70 lbs/min of airflow, which by very rough math would put you near to the 700 HP mark. This is with a stock throttle body with stock airflow scaling.
After scaling the TB airflow model down to 35% of stock, I am now seeing lbs/min readings of just over 40, which is obviously a lot more reasonable to believe. But, I'm certain that the TB airflow model is inaccurate and hacked at this point.
But all that aside, I am still seeing the fluctuations in TPS% and TPS Voltage trend (though in the voltage trend, they don't appear nearly as severe as the TPS%).
As for the MAP signal, I am at nearly 5000 ft elevation. KOEO, my MAP reading is usually around 85 - 86 kpa.
Here's the log from the Throttle Body Airflow Model rescale.
throttle_fluctuation.PNG
Throttle_fluctuation_test_3.hpl
Edit: Interestingly enough, I realized after I tested the airflow model rescale that I never rescaled the Large Range throttle table to reflect the model rescale. It didn't seem to affect anything in the way it ran vs normal. Nor did it throw an ETC error on the dash. Odd... I always thought those tables needed to match up.
Edit 2: I also checked with the newest beta, and didn't find throttle torque source as an option. Though I did find Powertrain Throttle Torque Request. I don't see much of a correlation between throttle torque request and throttle tps fluctuations.
Last edited by B00STJUNKY; 07-24-2018 at 12:39 PM.
Also, in regards to logging other potential PIDs for airflow, I don't believe the NGC3 PCM has those options you are referring to. Seems they are pretty limited, especially where it comes to enhanced PIDs.
Here's a list of all the PIDs available for my PCM under the Airflow dropdown:
airflow_PID_options.PNG
How it calculates airflow is a great question.
I can only figure that it's calculating it based on manifold pressure and rpm X VE%. Stock it would have a known value for VE.
The only other way I can see it calculating airflow is using a known injector flow (what it came from the factory with) and lambda data to work backwards at part throttle and applying that to WOT mathematically.
And since this engine has a different VE, MAP has been rescaled, and injectors are bigger - a lot of those numbers are probably out the window.
But maybe there is something else?
I wonder if adjusting the Min PHI to 1.000 would help at all. (13554) Airflow>Electric Throttle>Min Phi. I often will set this and the proportional gain table all to 1.00 when I have an unstable throttle blade but normally I only need to do this with a whipple blower.
Just so I'm clear, which proportional gain table are you referring to?
The only one I'm seeing for the ETC system is in the idle portion of the calibration.
Sorry I guess this only has the min phi and not the gain table found on the WK2's.
Went out and did a little more testing. Found a huge drawback to having the throttle body model rescaled to 35% of stock. It makes the part throttle react very inconsistently. For example:Drunk_TB.PNG
Notice how even keeping the pedal steady (as much as I could), the throttle pretty much went WOT momentarily, then back to sanity, then back to WOT again.
Made for a very unpredictable ride. So, I scaled it back up past stock values where it seems to run best without throwing any ETC light on the dash (max airflow is around 10000 lbs/hr vs stock 8500 lbs/hr). No more unpredictable throttle. Back to having crazy swings in the "Total Airflow" PID, but I'm giving up on figuring that one out for now. Same with the TPS showing some dips. I have pretty much ALL torque management disabled at this point, and it still dips here and there.
Just a quick little update to this thread, even though it's not entirely relevant to the original query. I found the source of my inconsistent Throttle % during WOT. I looked through countless tables and even downloaded several other folks tunes just to see what all had been done with torque management, only to find that nothing was out of the ordinary, and I didn't appear to be leaving anything on the table where it comes to TM.
As an aside, I've been dealing with an infrequent ETC light illuminating on the dash from time to time. It was more frequent before I had gotten my idle issues squared away using the Torque/Airflow Factor table in lieu of hacking the Throttle Body Airflow model. So, I thought that maybe the remaining instances of tripping the ETC light could be ironed out with more massaging of the Torque/Airflow Factor table. But then I began to research the "set conditions" for this light, and reaffirmed that it's not only calibration issues that will cause this light to illuminate, but also electrical faults. This brought my thoughts back to the inconsistent Throttle % during WOT conditions.
I went back and checked some logs from a year ago, and noticed that WOT was rock solid, no fluctuations. Right up to the point where I pulled the heads off the engine to check valve stem seals and cylinder condition. I then discovered it was only after reassembling the engine that I started seeing Throttle % fluctuations at WOT.
The culprit? A loose TB connector. DUH!!! That makes sense.
Thinking back, I remember trying to seat that connector while reassembling the engine, and it was giving me grief (wouldn't seat and clip into place). So, I just now went out into the garage and wiggled it around, noting it was loose. Pulled it off, and re-connected it. What do ya know? It seated and clipped into place.
Man, I can't believe some of the stupid, simple things I overlook when doing big jobs like that. But, I'm glad to finally have that issue figured out and solved.
As for the airflow, well, I still don't understand why it's so erratic. I still somewhat suspect a reporting error in the VCM Scanner (maybe an incorrect scalar for the conversion factor, or a resolution issue - I don't know). Whatever the case, it doesn't seem to have any negative effect on anything.
Thanks for reading, hopefully this information ends up being useful to someone some day.
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