Gas mileage horrible after custom ECU tuning - Saab Performance Bulletin Board - Saabnet.com
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Gas mileage horrible after custom ECU tuning
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Posted by Saabpilot [Email] (#134) [Profile/Gallery] (more from Saabpilot) on Fri, 15 Feb 2008 18:18:43 Share Post by Email
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I posted once before, but need more advice. I had my ECU custom programmed at the SOC this summer by one of the prominent shops. On the trip home at 85 MPH I got over 30 MPG. Previously, with my bike rack on my roof I'd gotten about 25 - 26 MPG. After that trip home, my MPG has steadily declined and has bottomed out at 23 MPG. This is horrible and is much worse than before the ECU tuning. This is a highway car and 23 MPG is totally unacceptable.

This is calculated MPG, not what the SID shows me (but they happen to be the same). I have not changed my driving style. I recently had the car in to my very well qualified local indie and he verified there is nothing mechanically wrong with the car. I had him replace the plugs with new NGKs just on principle sake. The DI cassette was replaced before the convention and was a Saab OEM one. So neither of these are the culprit.

I've talked to the shop that did the ECU programming and they don't have any idea other than the air mass meter. My indie tested it, and it's fine.

Would there be any benefit to me resetting the ECU by disconnecting the battery? Did I cause this problem by driving 85 MPH on the way home from the convention...in other words did the ECU "learn" to operate most efficiently at this high speed, at the expense of lower speeds?

If I do disconnect the battery, what is the best way to make the ECU re-learn? I've read posts but not found the definitive answer on that question.

Thanks for any advice!

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