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Discussion Starter · #1 ·
So I know the answer and have an appointment at the dealer in the morning. But...Cobb cat back and Green Filter are the only (engine) mods. Battery was out for about an hour while I installed the shifter. Car sat about a week and did exhaust before any driving. Runs OK, but I felt like the fuel mileage was not reporting as high as it should. Now 160 miles after exhaust, I got a CEL. Car seems to run normal except for what I perceive as worse fuel mileage. Going to check the basics of stuff I took apart to get the batt out, but other than that! Any ideas? Did not pull any codes since I already have an appt for the morning.

Anyone have reduced fuel mileage following exhaust? Was getting easy 28+ On the freeway and now after a full day on the road today she's barely showing 25 if I'm lucky.

Anyways, just thought I'd throw it out for discussion. I have heard there's a timeframe for learning after having the battery disconnected. Could that be a player? Would you try disconnecting the battery again to see if it resets the CEL? I do not disconnect the battery during/after the exhaust install; would you have done that?
 

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Discussion Starter · #2 ·
Oh...I did install wheels & tires during this time too. Guess that could account for fuel mileage loss, but that seems remote, and extreme for his drastic of a loss on this tank. I didn't weigh the new setup but can't be much more. Tires are only .3" taller in dia over stock.
 

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I noticed my mpg went down a bit after my exhaust was put on. I can say 100% it was because I love to hear it so I am a little heavier footed than before :smile:
 

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Did you bugger an O2 sensor? Do you have an exhaust leak? Are you using more throttle because you want to hear the exhaust?

Pull up the CEL, if you trip one, and can read it, why wait?
 

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Im stage 3 on e30 custom e tune with upgraded charge pipes and a blow off valve relocation and still have no check engine or anything.

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Get the CEL from an ODBII scanner, that will definitely help, otherwise, you're shooting in the dark really.
CEL can come up for any sort of reasons: bad spark plug, dirty MAF, dirty air filter (which results in a dirty MAF), fuel cap loose, etc...
 
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