OLSD - Hptuners guys, iat fueling fix?
02-07-2014, 02:02 PM
#41
I messed around with the bistable quite a bit yesterday and could not come to a setting that I like what I ended up doing was installing a 4.7 K om resistor in the wiring which showed 57 degrees Fahrenheit and I drove the car around for an hour but like 60 miles on the car and the tuna spot on everything was great I had no variance is even letting it idle for 20 minutes at one point in a parking lot everything was happy and I know that isn't ideal for a lot of people and some others might even think it's stupid but I know these combinations really well and how far I can push them safety wise I can always check the attempts on a bowl on the dyno or at the racetrack and obviously I'm not going to beat the **** out of the car when its 20 degrees outside also if I'm concerned I can just install a methanol kit and I 80 is are almost the relevant at that point
Last edited by Forcefed86; 02-07-2014 at 02:15 PM.
02-07-2014, 05:15 PM
#42
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Heat soak is the issue. The purpose of the temp Bias is to skew the bias either towards ECT or IAT. GM's thinking behind this was that at low airflow the air has more time to heat up from engine heat transfer, thus the resulting manifold temperature was biased towards ECT. This is why the Bias table looks like a huge Nike swoosh. The problem is for the Bias to work as defined the IAT should not itself be affected by engine heat and should report actual ambient (or in forced induction cars, pre-engine bay air just after the intercooler) air temps. From that reading combined with the ECT you can then properly calibrate the BIAS table. The only way to truly make the IAT sensor work in the engine bay is to place the sensor in the intake manifold itself and set the bias table to 0 across the board which effectively makes IAT = MAT.
Just in case you don't know the acronyms:
IAT = Intake or Inlet Air Temp
ECT = Engine Coolant Temp
MAT = Manifold Air Temp (This is calculated by the PCM and is the resultant temp used in GMVE calculations)
In the end if you wanted to hack it, you could manipulate the IAT sensor calibration to limit it's range so that it didn't swing as much as it does now. (I don't personally recommend this because it is just what I said, butchered up hack).
Just in case you don't know the acronyms:
IAT = Intake or Inlet Air Temp
ECT = Engine Coolant Temp
MAT = Manifold Air Temp (This is calculated by the PCM and is the resultant temp used in GMVE calculations)
In the end if you wanted to hack it, you could manipulate the IAT sensor calibration to limit it's range so that it didn't swing as much as it does now. (I don't personally recommend this because it is just what I said, butchered up hack).
02-08-2014, 02:07 AM
#44
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Denmah, out of curiosity why did you install the resistor instead of flatlining the IAT calibration to always read 57 degrees?
02-08-2014, 02:41 AM
#45
Have you tried this? I was seriously considering this today, but I didn't think to set the bias table to 0. If so, what would you do to the "charge temp filter vs airflow" table? I'd assume max it out so that it reacts quickest?
Denmah, out of curiosity why did you install the resistor instead of flatlining the IAT calibration to always read 57 degrees?
Denmah, out of curiosity why did you install the resistor instead of flatlining the IAT calibration to always read 57 degrees?
02-08-2014, 05:55 AM
#46
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It's not just about heat soak of the IAT sensor, it gets over 100 in many parts of the country. I have this same problem with my blown Z. Tune is spot on but once the IAT gets above 90 it's game over. AFR gets to 16 and higher as the IAT gets higher. I always hear people say SD is so much better and a proper SD tune can be spot on in large temp and elevations swings.
If your VE table is spot on for normal IATs then what table is used to add more fuel for when the IAT gets above 90 in closed or open loop without using STFTs and LTFTs?
If your VE table is spot on for normal IATs then what table is used to add more fuel for when the IAT gets above 90 in closed or open loop without using STFTs and LTFTs?
02-08-2014, 01:44 PM
#47
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I have done the IAT inside the manifold and it does work.
I've not had afr swings personally once one of the two methods I said above have been done. If the IAT is outside of the engine bay and the bias is calibrated properly you will not see afr swings. I am in KY so we see 90+ deg in summer and currently it is 30 outside. I have not experienced this huge afr swing on my car in this temp range.
If you let your car sit and idle the MAT will go up some but the IAT should not go up if you are using the bias table. If it does then it is falsely heat soaking which will mess with the whole bias routine since ECT is a direct representation of engine heat. So keep the IAT from heat soaking or place the IAT inside the manifold so that it will directly report MAT.
On the filter table if you 0 the bias table the filter table doesn't really matter since the bias never changes from 0. The filter table only filters how quick the bias changes from its current value to the new value.
I've not had afr swings personally once one of the two methods I said above have been done. If the IAT is outside of the engine bay and the bias is calibrated properly you will not see afr swings. I am in KY so we see 90+ deg in summer and currently it is 30 outside. I have not experienced this huge afr swing on my car in this temp range.
If you let your car sit and idle the MAT will go up some but the IAT should not go up if you are using the bias table. If it does then it is falsely heat soaking which will mess with the whole bias routine since ECT is a direct representation of engine heat. So keep the IAT from heat soaking or place the IAT inside the manifold so that it will directly report MAT.
On the filter table if you 0 the bias table the filter table doesn't really matter since the bias never changes from 0. The filter table only filters how quick the bias changes from its current value to the new value.
02-08-2014, 04:39 PM
#49
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I have done the IAT inside the manifold and it does work.
I've not had afr swings personally once one of the two methods I said above have been done. If the IAT is outside of the engine bay and the bias is calibrated properly you will not see afr swings. I am in KY so we see 90+ deg in summer and currently it is 30 outside. I have not experienced this huge afr swing on my car in this temp range.
If you let your car sit and idle the MAT will go up some but the IAT should not go up if you are using the bias table. If it does then it is falsely heat soaking which will mess with the whole bias routine since ECT is a direct representation of engine heat. So keep the IAT from heat soaking or place the IAT inside the manifold so that it will directly report MAT.
On the filter table if you 0 the bias table the filter table doesn't really matter since the bias never changes from 0. The filter table only filters how quick the bias changes from its current value to the new value.
I've not had afr swings personally once one of the two methods I said above have been done. If the IAT is outside of the engine bay and the bias is calibrated properly you will not see afr swings. I am in KY so we see 90+ deg in summer and currently it is 30 outside. I have not experienced this huge afr swing on my car in this temp range.
If you let your car sit and idle the MAT will go up some but the IAT should not go up if you are using the bias table. If it does then it is falsely heat soaking which will mess with the whole bias routine since ECT is a direct representation of engine heat. So keep the IAT from heat soaking or place the IAT inside the manifold so that it will directly report MAT.
On the filter table if you 0 the bias table the filter table doesn't really matter since the bias never changes from 0. The filter table only filters how quick the bias changes from its current value to the new value.
02-08-2014, 05:13 PM
#52
It's not just about heat soak of the IAT sensor, it gets over 100 in many parts of the country. I have this same problem with my blown Z. Tune is spot on but once the IAT gets above 90 it's game over. AFR gets to 16 and higher as the IAT gets higher. I always hear people say SD is so much better and a proper SD tune can be spot on in large temp and elevations swings.
If your VE table is spot on for normal IATs then what table is used to add more fuel for when the IAT gets above 90 in closed or open loop without using STFTs and LTFTs?
If your VE table is spot on for normal IATs then what table is used to add more fuel for when the IAT gets above 90 in closed or open loop without using STFTs and LTFTs?
02-08-2014, 07:51 PM
#58
From what I just read the whole point of the ECT/IAT bias is for the computer to determine the IAT in the intake manifold. For forced induction cars the best place for the IAT is in the manifold with the ECT sensor having zero control of fuel.
I see shortuning already said this above.
I see shortuning already said this above.
Last edited by sbcgenII; 02-08-2014 at 08:22 PM.
02-08-2014, 08:32 PM
#60
I play with Bias on all vehicles that have issues...
moving towards 0.0 makes it more IAT...moving it towards 2.0 moves it more to ECT..
in general, you need less IAT influence than stock....
which means 0 is the wrong direction...
you will have big swings with it at 0...
making it less IAT dependent is the key...
fuel is influenced by heat within the engine and the fuel lines...fluids(fuel) are very efficient at passing heat from one surface to another.
air...is a very very poor conductor of heat...(perfect example is a hair dryer..takes 1800 watts to convert 70* room temp air to 100* air to dry your head)
Thermal Conductivity [k - W/(m.K)] of Gasoline is around 0.15
over 6x more than Air at sea level is only 0.024
the air itself moves too fast to pick up any measureable heat...even at idle
any hot air you get it actual hot air being pulled in from somewhere
the bias table was a way to solve the problem of the fuel/air mixtures variance in heat because of 2 main things....
fuel contact to the Hot engine parts (stock, we spray gas on the back of the valve to evaporate it and make for better emissions...blah blah blah...)
and because the fuel has time to pick up heat in the tank and fuel lines (and this is where it picks up most of its heat from)
usually moving bias to a value closer to 1.0 yields decent results...
dont get confused with IAT vs MAT....
they essentially are the same thing...
your ECU knows IAT based on a sensor
MAT is Calculated, and it is only correct if your Bias table is correct...
the way a VE table works is based on the MAT value....so if your Bias is off.. your MAT is off...your tune swings with IAT changes.
even if you locate your IAT sensor directly into the intake manifold, you will still need the bias table to be higher than 0 because the fuel will pick up some heat from the surfaces it contacts before it gets sucked into the cylinder...remember it picks it up 6x faster than the air can...and spends considerably more time in contact with hot surfaces
moving towards 0.0 makes it more IAT...moving it towards 2.0 moves it more to ECT..
in general, you need less IAT influence than stock....
which means 0 is the wrong direction...
you will have big swings with it at 0...
making it less IAT dependent is the key...
fuel is influenced by heat within the engine and the fuel lines...fluids(fuel) are very efficient at passing heat from one surface to another.
air...is a very very poor conductor of heat...(perfect example is a hair dryer..takes 1800 watts to convert 70* room temp air to 100* air to dry your head)
Thermal Conductivity [k - W/(m.K)] of Gasoline is around 0.15
over 6x more than Air at sea level is only 0.024
the air itself moves too fast to pick up any measureable heat...even at idle
any hot air you get it actual hot air being pulled in from somewhere
the bias table was a way to solve the problem of the fuel/air mixtures variance in heat because of 2 main things....
fuel contact to the Hot engine parts (stock, we spray gas on the back of the valve to evaporate it and make for better emissions...blah blah blah...)
and because the fuel has time to pick up heat in the tank and fuel lines (and this is where it picks up most of its heat from)
usually moving bias to a value closer to 1.0 yields decent results...
dont get confused with IAT vs MAT....
they essentially are the same thing...
your ECU knows IAT based on a sensor
MAT is Calculated, and it is only correct if your Bias table is correct...
the way a VE table works is based on the MAT value....so if your Bias is off.. your MAT is off...your tune swings with IAT changes.
even if you locate your IAT sensor directly into the intake manifold, you will still need the bias table to be higher than 0 because the fuel will pick up some heat from the surfaces it contacts before it gets sucked into the cylinder...remember it picks it up 6x faster than the air can...and spends considerably more time in contact with hot surfaces