andy670ho

iTrader: (3)

My car has a K&N cold air kit on it and before I modified my radiator support to get direct cold air to it my iat's were always running in the red on hptuners like above 100 degrees, now the iat is registering whatever the temp is outside. It has been cold here so it is reading in the 40's and 50's. I have noticed on my wideband that it has gone a little lean. Can lowering iat temps this much cause this, even at wot it is about .4 to .5 points leaner.

RoDan

Yep, and the reason is because these cars work backwards from what would normally be considered intuitive.

With a carb, colder temps mean leaner and vice versa.... well with LSx pcms at least, when the computer sees colder temps, it pulls fuel. So with a lower IAT reading, it will pull fuel making your car go leaner.

The reason it pulls fuel is because of the way the MAF works. Basically, it is referenced from the IAT temps and based on what temp the IAT reports, it can calculate how much air is flowing over the MAF wires (which are heated to to a consistent temp). Colder air cools things off better than hot air does, so the ecm interprets the colder reading of the IAT and tries to compensate by reducing the amount of fuel delivered, because if the air were in fact colder (but the same volume) the MAF would be reading higher than it is.... Colder IAT means colder air, MAF sees the same air but the computer uses the IAT readings to bias the MAF readings and thus the ecm thinks it is seeing less air, when in reality it is seeing the same amount just at a different percieved temp (still obviously the same actual temp). If any of that makes sense... lol

The only way to help alleviate this problem is to change the "Cylinder Charge Temp" bias settings, and skew them more towards ECT and less toward IAT. What I did was set the bias to 1.0 across the board, making an even split of IAT and ECT bias. This works best if the IAT is in a good location to see moving air, and not in a dead spot in the air box for example. You will likely have to re tune your VE though.

However, in SD mode, it still maintains this odd behavior despite the lack of a MAF sensor. I think it is probably due to the fact that these cars were never designed to run in SD mode, and therefore this behavior is kind of hard wired into them and can't be fixed unless you use some custom OS or something of that nature.

Dabeztz28

iTrader: (27)

I had same issue with the k&n filter. IATs where in the 130s, but the only table I found on hptuners that was affected by the high IATs was the iat spark table, which reduces timming. But temp does have an effect since the car runs leaner during the day here in AZ, and a lil richer at night when it gets cooler

Dabeztz28

iTrader: (27)

I also modified the radiator support for direct airflow

RoDan

Exactly. Backwards from the way a carb would behave. The table to change would be the charge temp bias table like I mentioned earlier. Bias it more towards ECT, and it will help minimize the effect. The bias is simply not correct, if it was dead on you would keep the same AFR just about all the time. Even GM didn't have it right from the factory. Too many variables. All you can do is guess, that or use a potentiometer as a "temp selector" and dial in whatever temp is outside manually and disable the complex model so it will only look at the IAT.

WeathermanShawn

iTrader: (1)

I guess I have had a much difference experience with IAT's and fueling than what has been described.

Warm I go leaner, cold I go richer (via Trims/wideband). What you also might be experiencing is as you have added additional airflow and your IAT is closer to ambient (colder), the engine is wanting more fuel to burn the charge. That is why many people re-calibrate their MAF Table after any change in front of the MAF.

Think about it. It is leaner, because it wants more fuel. Colder air is more dense than warm air. If it is lean, it wants more fuel. Even changing to an Lid or K&N filter usually make you tend toward lean. You have enhanced the engines ability to ingest air, but have not re-tuned it to re-calibrate the additional fuel required.

Though some have had success altering ECT/IAT bias tables, personally I would want my engine to take advantage of colder IATs. That was your point in adding a cold air intake system.

Depending on whether your SD, MAF, closed or open loop will determine which way you need to go on this.

Perhaps some others will chime in, but that has been my expierience.

Good luck.

..WeathermanShawn..

turbolx

Guys, there's no need to go off on some tangent and invent new physics/science along the way.

If the MAF is active, it doesn't care what the temp is. It's already temperature compensated by design. The error you're seeing is because you changed the way air enters the MAF element through the new filter and tube arrangement. You NEED to recalibrate the MAF airflow vs frequency table (in steady state!) to establish the new curve that matches your hardware. This should be done in open loop using a good quality wideband before making any other changes.

For SD, you just need to leave the IAT-ECT temp compensation and sensor location near stock while correcting the VE table (in steady state!) with a wideband in open loop.

If you get these two main changes right, lots of other little quirks like the temperature influence you're seeing will fall into place. Don't make this harder than it needs to be...

Gh0st

iTrader: (3)

Yout got that backwards.

Colder IAT = richer
Higher IAT = leaner

You should only experience this in OL with a non-perfect bias table. In closed loop with MAF, UNLESS YOUR TUNE IS WRONG AND YOUR FUEL TRIMS ARE POSITIVE, your measured air fuel should not change.

Gh0st

iTrader: (3)

Setting the bias to 1.0 is telling your computer to ignore IAT.

RedHardSupra

iTrader: (1)

while I agree with the first part 100%, the second part bugs me for multiple reasons:
what if you have to move your IAT, like a super/turbo charger?
if you're correcting VE and the bias at the same time, how do you know how much is each factor contributing?

RoDan

no, setting it to 2.0 would do that.... and 0 would make it ignore ECT.

Notice how the OP mentions that the ECM is seeing a colder temp, when in reality the temp has not changed just the temp the IAT sees has changed (the air going into the motor is the same air). Why would the ECM be fine at seeing 100* IATs with 50* air, and when the IAT sees 50* temp at 50* air, it goes leaner? It should only be adding fuel, since colder air = more O2 = need more fuel. Trust me, these computers work backwards compared to a carb, and it takes getting used to.

Frost

iTrader: (45)

Further... VE aside, how do you solve for bias anyway, particularly in a relocated position as mentioned? How on earth do you describe and control heat soak?

RoDan

Precisely.

andy670ho

iTrader: (3)

All I changed was something similar to the above post with the mesh in the support, thanks for all the replies and can someone look at my tune and see if something is off causing this.

WeathermanShawn

iTrader: (1)

To the Op.

Sounds like if your MAF enabled, you need to recalibrate your cylinder airmass vs MAF frequency to get the proper fueling and spark load.

RoDan, I am not sure I am totally following you.

g/cyl = VE*MAP/charge temperature.

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.

Few times I have done open-loop SD tuning, higher charge temperatures have always resulted in less airmass. Idle for 1-2 minutes on a hot day (open-loop) and watch your AFR go leaner and leaner as ECT and a heat-soaked IAT sensor increases.

We are probably getting off the OP's question, but it sounds like you have a different approach.

Andy, hope it works out for you. Best of luck.

..WeathermanShawn..

Gh0st

iTrader: (3)

Then there must be something different in the 04-06 GTO computers that does the exact opposite of what you're saying. When the IAT is high, car goes leaner, when the iat is low, the car runs richer. In OL of course.

You are correct about the bias though, my mistake

Gh0st

iTrader: (3)

Wow, someone actually had the common sense to realize the OP changed his intake tract and therefore his MAF is thrown off! GEE I WONDER WHY HE'S RUNNING LEANER

Gh0st

iTrader: (3)

Don't waste your breath. He is contradicting himself.

In his first post he says:

"well with LSx pcms at least, when the computer sees colder temps, it pulls fuel. So with a lower IAT reading, it will pull fuel making your car go leaner."

Then he completely contradicts himself by AGREEING with this statement:

"But temp does have an effect since the car runs leaner during the day here in AZ, and a lil richer at night when it gets cooler"

Maybe he's had too much

andy670ho

iTrader: (3)

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.

RoDan

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