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I have an 03 C4 cab with the X51 engine. Normally runs very smooth with no problems until I filled up with a tank of Sunoco 93 the other day. I usally run Shell premium. Now I have a hesitation when accelerating in any gear and also a very sharp surge around the 3200 mark. I understand that this is normal to get a small surge but this has become much worse. Then to add to the mystery I checked the computer mpg which is normally around 23.5 mpg and now it has jumped to 25.6 mpg. I hate to complain about good gas mileage but something is not right.

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I don't think the Sunoco 93 would do that on its own. Something might have contaminated the gas (like a recent underground tank re-fuel that stirred up something at the bottom). If that is it and the fuel filter is partially clogged, the in-tank filter will be a :censored: royal PITA to remove and replace. Hope it is something simpler. No codes?

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Thanks for the reply. No codes yet but you may be on to something with the bad gas. It seems like the engine is running way too lean what with the hesitation and incresed mpg. I'll post again after I refill with new gas,

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