eco reset resulting in higher mileage?? - Fuelly Forums

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Old 08-10-2007, 06:50 PM   #1
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eco reset resulting in higher mileage??

battery went out on me and i replaced it. also right after that i had trouble with brake light switch staying on and corrected that too. battery was disconnected for 8 hours straight then drove home and disconnected again for 3 hours till evening. ever since then i have been seeing better readings on my scanguage.

also finaly took a trip that got engine heated up and that was realy impressing me with the numbers i was getting at steady speeds. usualy i only see water temps in mid 180's well i was seeing 200-205 at speed. i was staying at 5 under the limit of 45-55 mph.

*title should read E.C.U Reset
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Old 08-10-2007, 06:56 PM   #2
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HMMMM i wonder why?
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Old 08-11-2007, 06:11 AM   #3
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I recently replaced my O2 sensor. It was recommended here at gassavers, that I disconnect the battery to reset my ECU, so it could 'learn' the new sensor. That made sense to me, since I knew the ECU had to average the signal from the sensor. After reconnecting the battery, the fuel GPH was all over the place for several days. And it took two weeks for it to settle down completely. I found my idle GPH was down from 0.4 to 0.3. and I could see a 0.4 GPH decrease on the highway too.

I attributed this gain to the O2 sensor. But perhaps you've stumbled onto something else. Maybe the ECU needs to relearn an older sensor, as its signal has changed. Wouldn't that be funny if Bosch lost half the sensor market because people stopped replacing their sensors, and just reset their ecu.

Seriously, it would be nice if some more folks would reset their ECUs so we can give this a good test.
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Old 08-11-2007, 06:36 AM   #4
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A failing battery will play havoc with the electrical system, and can take a long time to show up. It can also drag the alternator down. Replacing with a new battery may be the fix because the alternator won't have to work as hard and the computer will be getting a constant voltage.

NOTE: If the alternator fails in the next week, replace both the battery and alternator at the same time. My standard procedure is to replace both together, after a nasty incident I had where I replaced 4 batteries and 3 alternators. Turns out that the problem was I had a bad battery, and the alternator cooked itself trying to keep it charged. When I replaced the alternator, the battery had drained too far, which then cooked the new alternator, which didn't show itself until after I had to replace the battery, ect. It was a vicious cycle that didn't resolve itself until I replaced both together. Once I did that, I had no further occurrences. Luckily for the replacements were all warranty issues, but that was still a lot of useless work. Now this won't necessarily happen every time as I've had batteries and alternators fail in the past without taking the other one along, but I'll not go through that again.
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Old 08-11-2007, 08:17 AM   #5
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Quote:
Originally Posted by Telco View Post
A failing battery will play havoc with the electrical system, and can take a long time to show up. It can also drag the alternator down. Replacing with a new battery may be the fix because the alternator won't have to work as hard and the computer will be getting a constant voltage.
Good point there Telco!

A failing battery can also reduce you FE numbers and also tend to "boil" water out the caps.
I check my cars battery with an old analog battery charger ever time I do an oil change. What I'm looking for is how fast the battery amp draw drops off and at the same time how quickly the battery comes up to the normal regulated voltage for the specific car.
On my 4Runner thats about 14.3vdc. I expect the battery to come up to voltage in about a minute or two and watch it with a DVM. If it don't it may be sulfated and need some long and slow charging to help that or its just going bad. Weak battery's may sit for hours on end drawing 3-4 amps and never come up to the proper voltage and that hurts your FE and "boil's" out the water at the same time.
My new favorite battery is the AGM type since they take a charge very quickly, tolerate getting cycled and never boil. Thats why I'm running an Optima battery.
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Old 08-11-2007, 12:27 PM   #6
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I don't know. Just have to see when i refuel if they are for real or maybe the settings changed somehow when battery was disconnected.
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Old 08-11-2007, 12:32 PM   #7
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I think i might get a new battery soon so ill test it then.
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Old 08-11-2007, 07:34 PM   #8
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my shop manual recomends removing the fuse that resets the ECU, or removing the battery cable while doing almost any work on the engine or sensors, I don't do it as often as I should, but it seems reasonable.
I think a number of more sensitive sensors run off 5 volts, and have a low voltage power suply to step it down for them so the sensor can be more acurite, it's also easier for the computer to be standarized.
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Old 08-12-2007, 11:25 AM   #9
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I'm thinking maybe old battery was was causing alternator to work more to recharge.
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Old 08-21-2007, 10:43 AM   #10
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Hmmm. So, if everyone thinks LxMike's increased FE was due to replacing the faulty battery, not from reseting the ECU, then I guess I'll have to attribute my FE increase to the new O2 sensor.

I'd still like to see some data from folks resetting their ECU's though, just to see if there is any effect.
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