A/F in winter compared to summer

[plumcrazy]

i know the cars run stronger in the cooler weather and im assuming it is from leaning out a little. is this true?

and if it is leaning out in the cooler weather isnt it true that its more likey to have detonation then?


thanx

 

[Anaconda]

Cooler air is denser. The A/F should remain the same, because the temperature is measured.

Detonation is more likely in the summer (hotter air) than the winter, but the A/F should remain the same.

 

[99 R/T 10]

Cooler air is denser. The A/F should remain the same, because the temperature is measured.

Detonation is more likely in the summer (hotter air) than the winter, but the A/F should remain the same.

I disagree, I thought that the cooler DENSER AIR would cause the car to run leaner(more air, same amount of fuel). I may be wrong, but that was my understanding.

 

[Anaconda]

Isn't that only true in carb. cars? I thought the O2 and MAP sensors were designed to measure density.

 

[plumcrazy]

im with 99 R/T 10 . i think it leans out in cold weather and therefore closer to detonation

 

[Anaconda]

What would be the point of measuring the air temperature then? Why would the car have the sensor if not for that very reason? And why have a MAP sensor either? Or O2 sensors?

 

[CANTDRIVE55]

Hi,

I believe that the MAP will correct the A/F ratio BUT the charge to the cylinders will be greater due to the greater air-density of cooler air (sort of like a little increase in displacement). The ratio of O2 molecules (a constant in air)to fuel molecules will be correct...just more O2 molecules per CC of air when the air is cooler.

 

[Jack B]

Without any correction by the PCM the a/f would get proportionately (follows the temp) leaner in cooler weather due to denser air, in other words the ratio of air/fuel would go up. I don't know about all cars, but, the viper PCM is not perfect and will allow approximately a full point (at the extremes) of change at WOT during the year. The more mods a cars has the worst it gets.

 

[plumcrazy]

thanx jack.

 

[Schulmann]

From my experience ...
Temperature here can vary from 20F to 70F the same day.



I posted a question a couple of weeks ago about this trouble but it didn't get much attention.

The problem is to start the engin and at WOT. Once the engin is running the PCM will maintain a very stable 14.7 during the idle and cruise no matter the temperature.


The PCM uses the Oxygen sensors to adjust its fuel map. The problem is when the temperature changes suddenly and I start up the engin. The engin will start with the old fuel map. The temperature sensor in the air box is nearly useless. It should adjust the fuel at the startup of the engin and during WOT. However it doesn't do it very well. When the engin starts with an offset fuel map it takes about 1-2 minutes to the PCM to adjust it. Then the engin runs perfectly.

The temperature sensor is a very weak point in the stock PCM.

 

[Jack B]

Schulman:

we are not worried by the a/f during closed loop. The temperature shifts only hurt us during open loop (wot). You could run all day at 15:1, 2000 RPM and 20" of vacuum and there is no foul. The problem is when the a/f is 15:1 and you hit 4th gear at wot, that is a foul.

 

[Schulmann]

I agree with you JackB but before you hit WOT you need to start the engin. And you will have some difficulty if temperature changes a lot while the engin was stopped.