IAT effect on afr
Launching!
Joined: Jan 2002
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From: Detroit, Murder City
Trying to adjust VE and ECT bias simultaneously is like trying to solve for two unknowns with only one equation. Pick one (VE) and solve for it first while holding the other (temperature) as close to constant so that the effect of the bias is minimized. You'll find that the factory bias tables are pretty close to ideal as long as the IAT sensor remains near the stock location as mentioned above.
So can someone point me in the right direction? Is my Maf not reading correctly and not compensating for the cooler air, should be adding fuel for cooler air right? If you look at my tune the original tuner has the iat parameters set at 0, will this void the iat readings for adjustment?
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From: Denver International Airport, Colorado USA
Do you mean by introducing air to the bottom of the air cleaner instead of pulling air from all around when the holes weren't in the support? I also have everything removed from the front of the car and the k&n is now getting clean outside air, before underhood heat soaked air.
If you ever log Trims, many of us have noticed that after adding a lid, filter, cold air intake, the Trims go positive. In my case it went to +15 Ltrims in one day after adding those modifications.
But, I would rather have the additional HP and adjust the airmass and fueling for it than put the stock airbox back on. Overall I think anytime you can get an IAT that is as representative of the air entering the engine it is a good thing. So, you did the right thing. It just seems to be a 'quirk' of the how a MAF functions. You would think it would require no calibration, but a car is not happy running +15 - +20 LTrims.
I have the other Tuning suite, so I am unable to download your tune. Perhaps someone else will look it over and comment.
RoDan, no problem. You are probably noticing the same problem with temperature bias many of us have encountered. Good luck with your bracket racing.
..WeathermanShawn..
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From: Denver International Airport, Colorado USA
Andy, I am using EFILive tuning software. I am unable to download your tune. Perhaps a fellow HPT user will look over your tune.
But in general if you are running closed-loop (using feedback from the narrow-band O2's) and your MAF is enabled (not running SD), you might be best to set your temperature bias tables back to stock.
Then I would suggest you look at over the PCM stickies at that point. It is not all that complicated, but you need to log Trims, AFR, etc. It would take several pages to write it out, so inexperienced or not just work your way through it.
Normally if you are running closed-loop your Trims will correct the the AFR back to 14.7. So, I do not know if your problem is at WOT or throughout the entire fuel curve. If you are running SD, you might need a more experienced SD tuner to guide you through. It is not that it is hard, but again you just have to do everything right.
You asked a very good question and perhaps we got off-track. Hopefully someone can look over your tune and help.
Best of luck.
..WeathermanShawn..
But in general if you are running closed-loop (using feedback from the narrow-band O2's) and your MAF is enabled (not running SD), you might be best to set your temperature bias tables back to stock.
Then I would suggest you look at over the PCM stickies at that point. It is not all that complicated, but you need to log Trims, AFR, etc. It would take several pages to write it out, so inexperienced or not just work your way through it.
Normally if you are running closed-loop your Trims will correct the the AFR back to 14.7. So, I do not know if your problem is at WOT or throughout the entire fuel curve. If you are running SD, you might need a more experienced SD tuner to guide you through. It is not that it is hard, but again you just have to do everything right.
You asked a very good question and perhaps we got off-track. Hopefully someone can look over your tune and help.
Best of luck.
..WeathermanShawn..
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From: Lexington, KY
Interesting thread. I will have to read it again when I am awake. I have been trying to figure this out. I am running EFI Live COS 3 and trying to tweak the IAT VS VE table.
I am running SD OL. My car definitely goes lean when the IAT temp rises when sitting in traffic.
I am running SD OL. My car definitely goes lean when the IAT temp rises when sitting in traffic.
Launching!
Joined: Jan 2002
Posts: 299
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From: Detroit, Murder City
The factory tune seems to be able to correct for just about any aircharge temperature between -40 and +120F. Perhaps it's a good idea to learn from their lessons... Aftermarket tuners get into trouble when they try to outsmart these functions and are left with only one equation with two or more unknowns.
Yes, we read a hotter temp with the "heat soaked" IAT sensor. Intuitively we look at this as lower potential aircharge, timing, and power as gearheads. The reality is that the temperature is what it is and we just need to react to it. If you want legitimately cooler air coming into the intake, change the filter location to a cooler place or improve the efficiency of your intercooler, but leave the sensor where it belongs so the actual aircharge temp estimation is correct. It's worse to have a false "cool" reading than a correct hot one as far as AFR and torque control is concerned. Once the airflow increases enough, the heat soaked IAT sensor become a non-issue.
If only someone had classes on this stuff...
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Verdad Gallardo Is there something magical about an aftermarket camshaft or cylinder heads that makes the aircharge not heat soak just like with the factory parts? Isn't it possible that the air in the manifold is really that warm occasionally? If so, we would want the appropriate correction, right?
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If that were the case, then the error must be in bias. In stop and go traffic when in OL, the IAT can rise pretty high and when it does, fueling wanders off lean. 3ish years ago, on an N/A car that I owned for a short amount of time I did some playing with it. As far as AFR consistency in OL, the car ran MUCH better and followed commanded fueling MUCH more closely when moving the sensor into the nose of the car and all together away from engine heat. In stop and go traffic, it didn't get hot and AFR stayed close to commanded. This is inadvertent 'bias tuning' (surgery with a chainsaw I know
) had a profound impact. If the air charge is REALLY the temperature that the sensor body is, and fueling wanders off, that only leaves bias tuning correct? 
[QUOTE=WeathermanShawn;11518144]
g/cyl = VE*MAP/charge temperature.
so according to this formula, the units of airmass are kPa/K . You see anything wrong with that? especially that you have grams on the other side? you're missing some vital pieces here
g/cyl = VE*MAP/charge temperature.
so according to this formula, the units of airmass are kPa/K . You see anything wrong with that? especially that you have grams on the other side? you're missing some vital pieces here
Launching!
Joined: Jan 2002
Posts: 299
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From: Detroit, Murder City
3ish years ago, on an N/A car that I owned for a short amount of time I did some playing with it. As far as AFR consistency in OL, the car ran MUCH better and followed commanded fueling MUCH more closely when moving the sensor into the nose of the car and all together away from engine heat.
the problem is that VE and temperature determine airmass. the fun part is that airmass determines the bias, which in effect determines the temperature. so you got some circular dependencies there.
treating one term as constant and adjusting the other and then swapping doesnt work, as the numbers keep changing and dont necessairly converge on a stable solution.
Though obviously we are more often tuning modified cars; yes, even on a completely stock car if you set it to OL you will see the exact same thing. The sensor body gets hot and fueling wanders off leaner than commanded. Drive for 30 mins, stop at a gas station and leave the car sitting for about 5 mins. The IAT's reported value will come up and the car will be lean on restart. Alternately slow driving and having to idle often will cause the same, even on a stock car.
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From: Denver International Airport, Colorado USA
[quote=RedHardSupra;11526162] Yes Marcin got sloppy on my units..I should have used the formula from your speed density paper. I got lazy and took a shortcut. I think everybody gets the fundamentals physics of air density and charge temperature.
After one year of attempting to construct a VE Table..the chasing of differing charge temperatures etc., it really seems like the only way to construct an accurate VE Table would be on the dyno with a controlled charge temperature.
We do it for spark and fuel. You do a street run for an hour and you are sampling differing charge temperatures for the same cell, regardless of how tight you think you have it.
We all probably make this a lot harder than it should be. My point on temperature bias is right in the middle of what Frost and Greg are saying. You want it to be representative, but we are no doubt getting some inaccurate heat bias at low speeds and idle.
Closed-loop gets a lot of negative comments, but Trims are an answer to this problem.
..WeathermanShawn..
After one year of attempting to construct a VE Table..the chasing of differing charge temperatures etc., it really seems like the only way to construct an accurate VE Table would be on the dyno with a controlled charge temperature.
We do it for spark and fuel. You do a street run for an hour and you are sampling differing charge temperatures for the same cell, regardless of how tight you think you have it.
We all probably make this a lot harder than it should be. My point on temperature bias is right in the middle of what Frost and Greg are saying. You want it to be representative, but we are no doubt getting some inaccurate heat bias at low speeds and idle.
Closed-loop gets a lot of negative comments, but Trims are an answer to this problem.
..WeathermanShawn..
Launching!
Joined: Jan 2002
Posts: 299
Likes: 41
From: Detroit, Murder City
We all probably make this a lot harder than it should be.
My point on temperature bias is right in the middle of what Frost and Greg are saying. You want it to be representative, but we are no doubt getting some inaccurate heat bias at low speeds and idle.
man... I did contradict myself. I knew what i wanted to say but it just didn't come out like I planned. I was just trying to say that it has been my experience that when the car should go leaner, it gets fat and vice versa. In OLSD or OLMAF I always see it behave unnaturally, and the best way i have found to remedy the problem is to use a bias of 1.0 across the board. I have been meaning to do some more testing though. I'm trying to get a good setup for bracket racing and I need a consistent car, or at least a predictable car.
I probably did have too much
I probably did have too much
Beer is good man, helps you relax after a hard day at work!
DING DING DING!!! We have a winner!
Is there an echo in here?
Precisely my point. The differences in estimated aircharge at a heat soaked idle (for a stock vehicle) are well within the allowable short term closed loop fuel corrections. THIS is what the corrections are there for from the factory, to correct for little inconsistencies in conditions you can't directly control such as temp soaks, fuel composition, or stackup of mechanical build parts within spec.
Is there an echo in here?
Precisely my point. The differences in estimated aircharge at a heat soaked idle (for a stock vehicle) are well within the allowable short term closed loop fuel corrections. THIS is what the corrections are there for from the factory, to correct for little inconsistencies in conditions you can't directly control such as temp soaks, fuel composition, or stackup of mechanical build parts within spec.
So I went to the track last night and my wideband is reading 13.3 to 13.5 at wot all the way down the track. Before I modified my radiator support it was always at 12.9, My IAT sensor is seeing outside air as my logged temps were the same as the temp gauge at the track. Can I just add .06 to the entire pe table to compensate for it? Is there a better way? I did get a few new personal bests last night with a 11.74 on motor and a 1.44 60 foot on the bottle. Is 13.5 asking for trouble? My mph was down, is this lean condition causing this?
Last edited by andy670ho; May 2, 2009 at 09:53 PM.
Teching In
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From: Florida
Though obviously we are more often tuning modified cars; yes, even on a completely stock car if you set it to OL you will see the exact same thing. The sensor body gets hot and fueling wanders off leaner than commanded. Drive for 30 mins, stop at a gas station and leave the car sitting for about 5 mins. The IAT's reported value will come up and the car will be lean on restart. Alternately slow driving and having to idle often will cause the same, even on a stock car.