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Discussion Starter · #1 ·
I have a 2009 Silverado ext. cab short bed 4x4 with a 4.8L V-8.

My question is, I have a scan gauge that reads various engine functions through the obd port. With all of my past vehicles (2 Jeeps and a Colorado), when no throttle is applied and the truck is coasting on a flat or downhill, my previous vehicles would show 9999 MPG. I asked a mechanic about this and they told me that the computer cuts off the fuel injectors while coasting to conserve fuel. My previous vehicles would show the 9999 MPG pretty much any time I was off the throttle more than a few seconds. My Silverado hardy ever shows this on the gauge. I have even tried going down long hills at a higher speed, but I can't seem to get it to activate. I have seen it register 9999 only a couple of times in the 2 months that I have owned it, so I know it does it, but I'm not sure why it doesn't do it more often.

Anybody have any insight in to this, the dealer didn't even know what I was talking about when I had it in for service.

Thanks
 

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If it 'cut off' the injectors you would have to restart the engine when you were done coasting. More likely the newer software is more accurate because my silverado doesn't have the instant MPG (i think cause i put it in myself) but my 08 G6 had the instantaneous and that never went to the 9999 either it would get up to the 100's sometimes but never go up to that high. My wife's loaded 04 envoy does do the infinite number like your talking about though when coasting.

Edit - are you getting the instantaneous off the reader?
 

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Discussion Starter · #3 ·
I am getting the instant MPG from the scan gauge. My previous Chevy, a 2004 Colorado would show the 9999 all the time, now my 2009 Silverado will only do it under certain conditions, like one section of road near my house it does it all the time on the downhill but only for a couple hundred feet. I can't remember who told me that the injectors were being turned off when the scan gauge showed 9999
 
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