jesseenglish

I know this sounds like a stupid question, everyones first thought is probably going to be, "Jesse, you've completely lost your friggin mind", but hear me out.

Your ATI Procharger was tuned at a certain temperature, elevation and humidity level, which all affect density of the air.

The sensor used to tell the fuel pump how much extra fuel pressure to add is installed inside the passenger compartment. Basically what I'm getting at is any time you change the atmospheric conditions inside your car you change the settings on the FMU. So, for this excercise I'm going to assume certain things to be true for now.

You tuned your car on a dyno with the AC off and the windows open.

If you turn on your AC, or even just the fan without the AC compressor running and close the windows after the tuning is done you've increased the atmospheric pressure that the FMU uses to reference ambient air pressure. Basically, it's the same thing as pressurizing the cabin in an airplane.

The way the FMU works is it compares ambient air (cabin pressure) to the pressure coming through the vacuum line from your engine compartment. As air pressure increases in the passenger cabin the FMU will see less of a difference between ambient air (cabin pressure) and your engine boost pressure. This could potentially cause the FMU to not not know there's as much boost and will can cause a lean condition.

Now before you fret about this, remember this is all theory and speculation on my part. Unfortunately, I have no way of testing the pressure variations between outside air and cabin pressure. What I'm hoping is somebody here does and can do the research for me. There is another way to insure this isn't a problem, install the Aeromotive FMU inside an weather resistant box in the engine compartment. That way there is never going to be any pressure differences that get affected by keeping cool in the summer.

Tomorrow, I'm also going to look into the possibility of installing a remote pressure sensor in the engine compartment.

If you have any thoughts on this please post and before you make any changes to your system, please reference the disclaimer in my signature.

jesseenglish

After thinking about it some more, I decided that everyone here should ignore my moronic post above. I have a simple way to test this theory. Do your ears pop when you open the door with the AC on. Mine don't, so it's probably not creating enough of a pressure differential to make any real difference. Too many leaks in the cabin for the air to escape. Sorry about my idiocy, it was late at night when I was thinking about this and I was tired.

peptidbond

iTrader: (2)

Jesse,

Your hypothesis makes sense. However, as far as pressure goes, there will be no increase. Here is why:

First, with everything closed and the AC set to fresh air, it still blows all the time. If pressure was truly building, it would stop pumping in outside air after a while. However, sometimes there can be a pressure difference.

At the rear of the car, just behind the two body panels on the right and left corners are small vents. I saw these vents when doing my dynamat and they vent outside. Hence, excess pressure is released out the rear. My Maxima had this too. Now, why is there occasionally a small pressure change? Well, the vents are behind tight body panels, so a tiny amount of pressure can build up. Make sense?

At any rate, at least this explains why you do not get a big pressure change. With AC on, the temp will be colder overall and the pressure would drop because of this. However, the vents can let a little air in the back, but they are not designed for this. The flange is weak rubber though, so some air could get in.

g356gear

iTrader: (12)

Wacky tobacky