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I don't know if anyone else has had this issue or would benefit from this experience, but here it goes anyway.

There is a stretch of road on my way to work about 1/2 a mile long. It's a gentle downhill. I can often take this stretch at 55 mph pulling 65-70 mpg (remember I said downhill). Every once in a while the car would feel like it was turning off. The mpg would peg at 99, and the car just seemed to die. If I gave it just a little bit of gas nothing would happen, but jut a little more it would cut back on and be about 60 mpg.

I spoke with the one ASE Certified Master Mechanic at our local dealership last week. He had no idea what it was, but was interested in finding out. I do not know who he talked to at GM about it, but he called me Friday and told me the answer.

Simply stated, I was getting too good mpg along that stretch. He said that the ultra high mpg was triggering the computer to do a fuel shut off. He said this is a rare issue, and only seems to happen in the 5 speed with the XFE "treatment". It's not a problem with the car, and is harmless.

His suggestion was that I pull it out of gear and roll, or just take the 60 mpg and be happy. A Cobalt is simply not ment to cruse at 65-70 mpg. :laugh:

I just thought this was a little funny.
 

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I dont know what your talking about the car feeling like its "dying," but when your going downhill the inertia keeps the engine going and therefore does not need fuel. That means you aren't using any gas, which will explain the 99mpg's you see in the DIC. If you have a wideband in the car you will notice it go completely lean when your foot is off the gas going downhill.
 

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I dont know what your talking about the car feeling like its "dying," but when your going downhill the inertia keeps the engine going and therefore does not need fuel. That means you aren't using any gas, which will explain the 99mpg's you see in the DIC. If you have a wideband in the car you will notice it go completely lean when your foot is off the gas going downhill.
x2 exactly what i was going to say
 

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Discussion Starter #5
I dont know what your talking about the car feeling like its "dying," but when your going downhill the inertia keeps the engine going and therefore does not need fuel. That means you aren't using any gas, which will explain the 99mpg's you see in the DIC. If you have a wideband in the car you will notice it go completely lean when your foot is off the gas going downhill.
Welcome to the forum.

Nah, I do not have a wide band. What was going on was that the downward slope is a VERY small grade, so if I let off completely the car slows down almost as much as if you were driving on a level road. It does take some power to keep going, but not much at all. I was on the gas so lightly that the computer was switching the fuel off like I was not on the gas at all even though I was. This is why I could feel the fuel cut off and it seemed like the car was dying.
 

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Discussion Starter #13
Oh yeah, I don't doubt your numbers, in fact I refer to them often. My point was just to let people know that if they are going real light on the gas and pulling real high mpg they can cause the fuel shut off to kick in with their foot still on the gas, and that it does not mean something is wrong with their car.
 

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I am so glad you found out what it was. It has been happening to me also on the hills that are too gradual to coast down in neutral.

It would catch me off guard getting 90+ mpg and then droping down to 55 mpg for 2 seconds and the car *coughing* as what I now know is the fuel shutting off.

I just feather the pedal a tiny bit to keep it from happening.
 
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