Maybe I'm having a brain fade but I don't see any direct relation to adjust fueling during closed loop vs intake air temp.
Is the only adjustment for this done in the cyl. charge temp. bias? ECM 13001
Do I also assume there is something going on in the back round HPT doesn't give us access to?
mischief 165 torque management change .hpt
Changes in air temp don't correlate with needing changes to fueling, only spark. ECT does though, both fuel and spark. That's why there are tables to adjust for ECT but not IAT.
Originally Posted by SiriusC1024
What problem are you having? Hot starts?
I have not seen any compensation for IAT other than the blend and filter. The IAT is directly inserted into the equation that derives VE.
This is the math I use to derive a VE value from the MAF, MAP and IAT. I start MAF only and actually log a histogram to create a startup VE table.
Dynamic air calibration from MAF
Dynamic Air Calculated =
(MAF gms/sec X 120) / (#Cylinders X RPM)
VE Calculation from MAF
VE=(DynamicAir X IAT in Kelvin X 0.28705) / (Cylinder Volume X MAP in Bar)
Now put both parts together.
VE=((MAF gms/sec X 120) / (#Cylinders X RPM)X IAT in Kelvin X 0.28705) / (Cylinder Volume X MAP in Bar))
VE Equation
[16.71] is HPTs way of inserting MAF in gms/sec
[12.56] is RPM
[15.240] is IAT in Kelvin
[11.99] is MAP in Bar
120 & 0.28705 are fixed values
8 is Number of Cylinders
0.7875 is volume of 1 cylinder in Liters
Not necessarily a huge problem I'm aware of.
My hot starts are acceptable enough for me now. They would not be good enough for someone who is not willing to tolerate 15 to 30 seconds of very lean behavior after a short to moderate heat soak.
What I am noticing that got me thinking about it, during the same ECT of say 180f
yet IAT near 50f, I am seeing 15 percent plus STFT compared to when the IAT are 90f.
I assume since cooler air is more dense, the engine would need more fuel to reach the same lambda target, assuming all other variables are close to the same. I also assumed the PCM is accounting for this in some manner.
It has been suggested to me to run my combo. in OL but this is one of the reasons I don't want to go strictly OL. I just restrict CL LTFT to min. positive change and little neg. change but CL STFT has much more room to operate.
Add 0.10 to your charge temp bias table for a start, add 10% each time after until the trims fall inline. No need to go over 1.0.
Actually, i see your table was set to 0. Try this change.
Last edited by 04silverado6.0; 12-31-2024 at 04:29 PM. Reason: Mistake
I also assume at this point, the cooler the air, the more oxygen will be present in the same intake trac. volume, at the same observed pressure, therefore requiring more fuel to reach the same lambda target, at the same observed load.
https://iopscience.iop.org/article/1...3/1/012039/pdf
As you probably noticed, the engine is boosted. It was suggested to me some time ago to bias the charge temp. more towards IAT. As you can see I ended up at zero across the board as a test and haven't moved it back. I did that before ambient temps. dropped significantly and never finished adjusting the VE table in the boosted areas and just assumed I would finish it next year. The IATs is in the charge pipe, about 6 inches before the throttle body.
By moving the bias more towards the ECT, I would expect the fuel trims move farther from the target. Why would you expect them to move in a negative direction closer to zero?
I guess my most immediate question now is, what exactly does the charge temp. bias table do, in the foreground and background and/or how does it work?
I made a mistake in my first post. If your iat is in the manifold you will set it to 0. I have had some issues with fuel trim variation on hot starts particularly in swaps with poor routing of intake piping. Raising the bias table will help offset that error on a hot start.
The table works basically how you would expect. With the bias towards iat you will have heak soak under the hood greatly interfere with fueling.
Mine behaves completely opposite of how you are describing. More bias toward the IAT compensation corrected the fueling dance with varying IAT readings. I have the factory GM airbox on my Express van. It will hit IATs of 200F in summer and as much as 140F in the dead of winter in 20F ambients sitting in traffic. I played with those IAT settings and got it tamed a good bit. Then ended up adding fuel to the post startup table that is referenced against IAT and Time to eliminate the hot lean re-starts.
With the OEM Express Bias and Filter it would run rich right after startup, lean out as the CTS increased, then richen up again as the IATs climbed. The IAT was not contributing enough at or near idle.
Just so we don't get too far off track, (although Fast4.7 reminded I could attack the heat soak restarts again from his angle) my observation is more at steady state scenario, such as 1600 rpm, 50 mph, light load, when fresh cool air is abundant.
The charge temp. bias table makes me think it is referencing something else. Such as when the IAT/ECT is "X" add or subtract from this table?
I believe the warm/hot restart lean issue is actually a fuel rail temperature/vapor issue from the stagnated fuel in the rail being somewhat of a mix of pressurized liquid and vapor rather than completely liquid fuel. After a short period of time the vapor is purged from the rail and replaced by cooler fuel. The IAT adder trick merely allows for added fuel delivery to compensate for that period of time. I first noticed that hot compensation used on a Vortec 4.3L from the factory. My first test was actually using the 4.3L values and it nearly eliminated the hot restart issue. At the time I was still running the OEM injection spider on a 350 and thus prone to the same heat soak as the 4.3L version.
The charge temperature calculation is odd for sure in the PCM.
273.15 + IAT + ((IAT-ECT)*Bias)
If the blend bias value is Zero the IAT is the charge temperature. If the blend value is 1.00 the ECT is the charge temperature. Both the IAT and CTS value changes are filtered by the filter term values. 0 is the slowest change and 1 is a fastest change. Generally speaking at higher airflow volumes the intake charge does not have as much time to be heated by the intake and cylinder head ports, thus the charge temperature shifts more and more toward the IAT as the airflow increases. The filter value also needs to change more rapidly with higher airflow mass.
If you are running the complex blend value created above it is substituted in place of the IAT value in the VE equation I posted earlier in this thread.
Last edited by Fast4.7; 12-31-2024 at 06:37 PM.
You're on the right track suspecting the complex temp model. Where is the IAT located?
In every vehicle ive made adjustments to this, going towards a ect bias richened the hot start. I have been able to raise the bias toward ect to the point of a slight rich overshoot which worked awesome.
"direct relation to adjust fueling vs intake air temp"
Not a per-engine thing, just hard science. Why dyno "corrected" numbers work.
I mean, you can cheat it with the sensor calibration. That would get what you asked for, but unless it's not calibrated right, leave it alone.
Last edited by MarcWolfe; 01-01-2025 at 12:44 AM.
This varies due to intake pipe routing and sensor placement. Compare a stock truck file to any gen 3 car or van and see the difference. A hot metal cold air intake behind the radiator on a swap will need this adjusted.
Agreed and an 8.1L is even more different because of its aluminum long runner intake manifold.
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