AFR issues at IAT temps over 105 F

I'm running a moderately modified 6.0 in my 99 camaro z28 and have been working the tune for a few months now. The tune is great on the street and I'm focusing now on 1/4 mile performance. Fueling at WOT is getting better ( working my way leaner slowly ) but I'm running into some inconsistencies in my data logs for actual AFR values (wideband) as compared to commanded values. At the track last night it was about 80 degrees and I was seeing IAT temps in the 120 range. The fueling went rich at these temps. With IAT temps below 100 the fueling was much more consistent and closer to the commanded ratio's. Letting the engine cool for 45 minutes made a big difference compared to a hotter engine run.

I know the the intake air temp will make a difference in fueling calcs but it goes off significantly after about 105. Is there any way to adjust for this or is this an ECM calculation that I've got to live with.

Letting the engine cool for 45 min between runs kinda sucks.

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Originally Posted by KDS

I'm running a moderately modified 6.0 in my 99 camaro z28 and have been working the tune for a few months now. The tune is great on the street and I'm focusing now on 1/4 mile performance. Fueling at WOT is getting better ( working my way leaner slowly ) but I'm running into some inconsistencies in my data logs for actual AFR values (wideband) as compared to commanded values. At the track last night it was about 80 degrees and I was seeing IAT temps in the 120 range. The fueling went rich at these temps. With IAT temps below 100 the fueling was much more consistent and closer to the commanded ratio's. Letting the engine cool for 45 minutes made a big difference compared to a hotter engine run.

I know the the intake air temp will make a difference in fueling calcs but it goes off significantly after about 105. Is there any way to adjust for this or is this an ECM calculation that I've got to live with.

Letting the engine cool for 45 min between runs kinda sucks.

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Odd the fueling would go rich from high IAT temps, typically it tends to lean out.

Check into the cylinder charge temp under the airflow table. its under Bias This tends to alter the fueling dependent on IAT/ECT values. A value of 1 will alter fueling based on IAT and ECT. Values less than one will be more bias to the IAT, more than 1 will bias more to the ECT.

Yeah, I thought the same thing, it should go lean. I'm seeing some long term fuel trims occurring when this happens, but not when the intake air temps are lower. I spent a lot of time on the VE and MAF tuning so I know they're accurate (values in the -2, -3 range).
I looked at the cylinder charge temp Bias table, the values are incredibly low for the entire range, going from 0.1714 to 0.0430. Not sure what to make of that? Any suggestions?

OK, so LTFT is going positive and then carrying over into PE....makes sense. I know some guys will disable LTFT altogether (keep STFT/closed loop enabled) for this reason, to avoid going rich at WOT. When I was running a supercharger and SD tune, I disabled LTFT because it would learn some funky values sometimes (maybe due to larger injectors? not sure). But it was a little finicky sometimes and didn't seem to function as well as stock form and just disabled them. Worked pretty well for me. I'm redoing my NA tune now, have LTFT enabled for now, but had a few cases of +3 trims or whatever causing things to go rich.... we'll see where I end up.

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Originally Posted by KDS

Yeah, I thought the same thing, it should go lean. I'm seeing some long term fuel trims occurring when this happens, but not when the intake air temps are lower. I spent a lot of time on the VE and MAF tuning so I know they're accurate (values in the -2, -3 range).
I looked at the cylinder charge temp Bias table, the values are incredibly low for the entire range, going from 0.1714 to 0.0430. Not sure what to make of that? Any suggestions?

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I know its not the right way but i run my bias ( for now) with 1.0 (even bias,) across the whole table. It seems to work ok for me.
My idle doesnt Lean out like it use to anymore.

My fix was to always run open loop and I put a variable resistor on the IAT wires so if I dont like the a/f ratio at any given moment I can just turn the dial until I do.
This also allows the IAT vs timing map to step in with any desired timing changes as you turn the knob. I have about 0.5* ish going in when I turn it "cold" for example.

Really helps with HPtuners because there is no real time tuning and I never have the laptop. So its sort of like a piggy back adjustment for fuel and timing with no laptop in the car.

I recommend around 1000Ohms, 500 wasn't enough adjustment and anything over 1000 seems to be asking for an accident if you every forgot it was turned one way or the other.

KDS i think i just ran into this issue on very hot days

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Originally Posted by anniversaryss

KDS i think i just ran into this issue on very hot days

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I was at the track on Friday and the temps were a bit cooler and I was able to keep my intake temps below 100, the fueling was pretty good. I didn't have time to change the bias values but I will this week before the next track session. Supposed to be a hot July here (for Canada anyway) so I'll update this when i get some more data.

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Originally Posted by KDS

I was at the track on Friday and the temps were a bit cooler and I was able to keep my intake temps below 100, the fueling was pretty good. I didn't have time to change the bias values but I will this week before the next track session. Supposed to be a hot July here (for Canada anyway) so I'll update this when i get some more data.

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A quick Update. Been to the track a few more times, has not been as hot, so intake air temps have not exceeded 100 degrees F. I did make the changes to the bias table (values all to 1.0) and I found that it altered AFR across the board to a slight degree but not significantly. The changes didn't result in any noticeable improvements so I returned the table values to the stock numbers.

Really you need to logging (or thinking about) the dynamic air temp (calculated temp of the air as it's passing the intake valve), that is the final value after it passes thru the blending factor math etc.

I believe a value of 1.0 makes Dynamic air temp = CLT. and 0 would dynamic air temp = IAT. Setting it to a value of 1.0 doesn't seem very wise, you're basically setting it up so fueling does not change or account vs IAT at all, since CLT is more or less constant. I can't imagine AFR will be on point come fall/winter time.

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Originally Posted by aaronc7

Really you need to logging (or thinking about) the dynamic air temp (calculated temp of the air as it's passing the intake valve), that is the final value after it passes thru the blending factor math etc.

I believe a value of 1.0 makes Dynamic air temp = CLT. and 0 would dynamic air temp = IAT. Setting it to a value of 1.0 doesn't seem very wise, you're basically setting it up so fueling does not change or account vs IAT at all, since CLT is more or less constant. I can't imagine AFR will be on point come fall/winter time.

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Thanks for the info, that's the first explanation of the function of the table values that I've gotten so far. So if that's accurate, yes the value of 1 wouldn't make any sense. The stock values are low decimal values which would then tend to follow the IAT values with a little adjustment for the engine temp, makes sense. I'll look for the dynamic air temp value, didn't know it existed, learn something new every time I log onto this forum.

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Originally Posted by aaronc7

I can't imagine AFR will be on point come fall/winter time.

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This is actually somthing like ve thought about. I noticed there are discrepancies with AFR with the weather changes.
Hot days might run richer than cooler days iirc

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Originally Posted by KDS

A quick Update. Been to the track a few more times, has not been as hot, so intake air temps have not exceeded 100 degrees F. I did make the changes to the bias table (values all to 1.0) and I found that it altered AFR across the board to a slight degree but not significantly. The changes didn't result in any noticeable improvements so I returned the table values to the stock numbers.

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How much did it change? I actually been wanting to revisit this table. Maybe go back to stock values but adjust to the idle are slightly so i dont see a real big swing at idle when temps get up

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The PCM calculates the charge temperature (in degrees Kelvin) using the following formula
273.15+IAT+((ECT-IAT)*factor) where factor is obtained from this calibration.

At low airflow "factor" is closer to 1 which weights the charge temperature in favour of ECT.
At high airflow (>150g/s) "factor" is closer to 0 which weights the charge temperature in favour of IAT.

The theory being that heat (ECT) is transferred from the heads and manifold after the IAT has been measured and prior to the air entering the cylinder.

If factor is 0, then the charge temperature will be IAT, if factor is 1, then the charge temperature will be ECT, other values for factor will blend the charge temperature between IAT and ECT accordingly.

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What sort of intake/IAT setup are you guys running?

If you are running LEAN on hot starts, it's most likely from the sensor/surrounding metal being heatsoaked and making the IAT reading higher than actual air temp. Getting the IAT away from hot metal sources and/or out of engine bay helps a bunch. This issue is very common I've found when using the standalone metal GM IATs and used in metal charge piping etc.

FWIW I'm using a LS3 MAF in a plastic/composite air intake (it's pretty well shielded from hot metal parts), and haven't touched my blend table...no issues yet on a SD tune (which is very temp sensitive).

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Originally Posted by aaronc7

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The PCM calculates the charge temperature (in degrees Kelvin) using the following formula
273.15+IAT+((ECT-IAT)*factor) where factor is obtained from this calibration.

At low airflow "factor" is closer to 1 which weights the charge temperature in favour of ECT.
At high airflow (>150g/s) "factor" is closer to 0 which weights the charge temperature in favour of IAT.

The theory being that heat (ECT) is transferred from the heads and manifold after the IAT has been measured and prior to the air entering the cylinder.

If factor is 0, then the charge temperature will be IAT, if factor is 1, then the charge temperature will be ECT, other values for factor will blend the charge temperature between IAT and ECT accordingly.

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What sort of intake/IAT setup are you guys running?

If you are running LEAN on hot starts, it's most likely from the sensor/surrounding metal being heatsoaked and making the IAT reading higher than actual air temp. Getting the IAT away from hot metal sources and/or out of engine bay helps a bunch. This issue is very common I've found when using the standalone metal GM IATs and used in metal charge piping etc.

FWIW I'm using a LS3 MAF in a plastic/composite air intake (it's pretty well shielded from hot metal parts), and haven't touched my blend table...no issues yet on a SD tune (which is very temp sensitive).

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Ok so EFI live seems to have better descriptions than HPT.
Basically your really using 0-1. 1 basically being ECT, 0 being IAT. Anything in between is a blend.
What about anything above 1. Both programs have a max value of 2.

Well, you have the equation right there in front of you.

If IAT is 100 and CLT is 200 and factor is 2.0, your dynamic air temp will be 300*F. It will give you garbage data and skew the rest of the tune.

Yes the value should be between 0 and 1. 0 at high airflow where heat transfer from the manifold/heads to the air will be negligible. And higher values with lower air flow.

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Originally Posted by aaronc7

Well, you have the equation right there in front of you.

If IAT is 100 and CLT is 200 and factor is 2.0, your dynamic air temp will be 300*F. It will give you garbage data and skew the rest of the tune.

Yes the value should be between 0 and 1. 0 at high airflow where heat transfer from the manifold/heads to the air will be negligible. And higher values with lower air flow.

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I'm running the stock LS1 intake components and the IAT looks to be well shielded from heat. I started this thread with the assumption that higher intake air temps were causing my AFR values to change (going richer than commanded) and the Bias table was mentioned as a possible contributor. After reading the latest reply's (thanks for your info, that explains the function clearly) the bias does not look to be the contributor. Looking at the stock data it looks to be good as is.

I added another thread a few hours ago with my latest tune and a data log. I'm not sure why it's going richer than commanded, any thoughts?

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Originally Posted by aaronc7

Well, you have the equation right there in front of you.

If IAT is 100 and CLT is 200 and factor is 2.0, your dynamic air temp will be 300*F. It will give you garbage data and skew the rest of the tune.

Yes the value should be between 0 and 1. 0 at high airflow where heat transfer from the manifold/heads to the air will be negligible. And higher values with lower air flow.

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Ah ok. This was completely explained wrong to me so i really appreciate the extra explanation. Sometimes i need a little more input.

I went to back to a stockish Bias table and it seems to be more consistent