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Old 11-08-2012, 06:29 AM   #1 (permalink)
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"Repaired" ECU drops 8-9 MPG

I had a coolant leak from the water pump and during the repair, the dealer noticed that the ECU was slightly out of spec. I was not clear at the time, but I think they made a "repair" by adding a resistor in parallel in the ECU (rather than replace it - which would have cost me ~$1,000!) - and now my FE has dropped from ~45mpg down to ~38mpg.

I have not seen mileage that low in 4+ years. I'm going to confirm that they did this, and ask if it can be reversed.

It is basically negating all my ecomods...

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Old 11-08-2012, 08:18 AM   #2 (permalink)
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What you mean out of spec? Now it's using more gas so it will pass the mot test?
Or they made some other mistake, not related to ECU. Same as when i disassembe/assembe some device, sometimes i have an extra scre lying around

I first read you got increase in FE I'm going to try that increase by replacing current ECU with Megasquirt in my car in next year
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Old 11-08-2012, 10:05 AM   #3 (permalink)
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The spec they wanted to fix had to do with a temperature threshold being a degree or so off. It was fine (other than a leaking water pump).
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Old 11-08-2012, 10:10 AM   #4 (permalink)
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It doesn't appear that you've run through a tank yet. It might just be that your SG calibration is off.
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Old 11-08-2012, 11:09 AM   #5 (permalink)
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if they did anything to the ecu, it will need to relearn your driving habits before you see optimum FE.
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Old 11-08-2012, 12:34 PM   #6 (permalink)
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Sometimes they will "flash" the ECU to the newest calibrations without telling you. Typically the newest calibrations decrease mpg in an effort to fix all of the "problems".
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Old 11-08-2012, 01:19 PM   #7 (permalink)
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Is this a Scion? Its my experience if you change anything to disconnect the battery for 15 minutes, then connect, start it and leave it idling for a half hour so it relearns everything.

Sounds kind of odd a national car dealer would go through the trouble to add a resistor vs just replace the whole ecu.
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Old 11-08-2012, 07:17 PM   #8 (permalink)
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The new ECU would have cost me ~$1,000, so no thanks. I'll keep you posted.
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Old 11-08-2012, 07:23 PM   #9 (permalink)
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My first thought was, perhaps a sensor didn't get hooked up again and it's never going into closed loop... don't know what they did though.
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Old 11-08-2012, 07:25 PM   #10 (permalink)
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What symptoms were present with the "slightly out of spec computer". If there was no check engine light or codes present, I think it is crap, frankly.
What was the justification for the "repair".
Federal emissions law requires them to replace a defective ECU for 8 years and 80k miles.
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