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Old 02-26-2009, 08:14 AM   #1 (permalink)
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MPG goes to 99999 when coasting

Well, my 95 Saturn SW2 is proving to be a PITA. We got the VSS issue resolved, that was nice but another thing that hasa been happening since day one is if I crest a hill and begin coasting down my MPG goes to 99999, also if I am going fast and apply the brake slightly it goes to 99999. Of course I can't calibrate my unit with this because the few seconds it goes to 99999 it makes my tank mpg skyrocket.

I am concerned that it might be a math problem caused by the fact that unlike other saturns using uSec/Gal 0289967320 I had to try 0029967320 which is much lower to get my readings within an acceptable range.

I messed around with the injector delay and it seems to affect mp MPG readings. I would like to know more about this value and how it affects the readings. DOes it have to do with what part of the pulse it is counting?

Any suggestions would be greatly appreciated.

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Old 02-26-2009, 08:24 AM   #2 (permalink)
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Are you sure it's not going into DFCO (engine braking)? If you're going, say 55MPH, and you just let off the gas completely, the car should engine brake, and it uses no gas when that happens. If you're putting it in neutral and it says 9999MPG, then that's probably not right, but as long as you're in gear, enjoy the high MPG .
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Old 02-26-2009, 09:41 AM   #3 (permalink)
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like mcTimson said, a lot of vehicles will shut off the injectors when coasting in gear, until some lower threshold speed is reached. I can usually hear it pop back on in the exhaust. Try coasting down from 50mph to 10mph and note what speed the mpg (or gph) reading comes back, using the stock injector delay configuration.

the injector delay is a value that is subtracted from the length of each measured pulse. To account for the mechanical delay of the injector opening. I wouldn't mess with it unless you cannot get the fuel dialed in after a few tanks and careful refill and adjustment procedures.

Can you check one thing for me though? Can you unplug an injector and check the ohms of the injector?
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Old 02-26-2009, 02:34 PM   #4 (permalink)
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Is it showing 99999 in the Instant display only? Or do you see it in Current & Tank as well? What happens to the "GH" reading in the Custom display when coasting? That's the GPH=gallon per hour.

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