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Discussion Starter #1
I have a 2017 with about 12000 miles on it. Picked it up Dec 31 2016, and almost since day one my wife has been saying it backfires. Asked the dealer about it a couple of times but they found nothing, so I thought I would mention it here. I don't really usually notice it but my wife asks if I heard it that time frequently. The situation it happens 95% of the time is from a stoplight or a rolling stop at a light when turning left, about 3/4 of the way through the turn, especially if I ease off the gas it will make a sound not loud more like a putt and a little jerk. On occasion it will also happen when going straight from a light if the traffic moves then slows down and I need to take my foot off the gas and the put it back on. That is more like a stumble trying to pick a gear than when cornering though.

I suggested earplugs for my wife but she didn't like that idea>:D
 

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Turbo equiped??.................

I'm not familiar with the 2017 smart with turbo. I do know that most cars with a turbocharger on the engine have a
"waste-gate" also. That prevent overboosting,when you reduce the throttle suddenly. Makes a pop sound that you may
think is a backfire?? Any 453 owners want to comment...................
 

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Backfires, in the OLD days, usually meant bad gas. Is that a possibility here?

91 octane or higher, right, for the turbo? Mercedes, like most, also recommends top tier.

Either that or your car is running rich. Someone tune it before you got it? Vroom vroom!
 

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My 451 occasionally backfires because the cylinder 1 spark plug is hilariously worn and it misfires. My 453 does not exhibit the problems you describe, so there's probably something going on in there. Sadly, this is one of those issues the dealership isn't likely to do anything about without a check engine light. And it seems the threshold before a misfire causes a CEL is pretty big.
 

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Discussion Starter #8
Good gas

Backfires, in the OLD days, usually meant bad gas. Is that a possibility here?

91 octane or higher, right, for the turbo? Mercedes, like most, also recommends top tier.

Either that or your car is running rich. Someone tune it before you got it? Vroom vroom!
I got the car New custom ordered 3 days after my 2008 was rear-ended at a stoplight. Since day one only filled with Shell V-Power NiTRO+ 95% of the time at the same station. I think the turbo gate, it it has one, could be it though. To me it does not sound loud enough to be a backfire.
 

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Discussion Starter #9
Always economy mode

When this happens, are you driving in economy mode?
I always drive in Economy mode. I watch the mileage close so don't use Sport mode. That said If I don't run the air and catch all the lights I typically get 42-48 MPG on my way to work. If I have the air on and hit all the lights that will drop to 30-35. If I take the highway to work and run 65 I get between 45-50 MPG. Best I have gotten is from Raleigh to Santee SC for the eclipse 3 hour drive at 60mph got 52 MPG.
 

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I had the same backfire problem with my 453. Manufactured 07/15. It also sometimes would pause when I needed to accelerate - especially when I needed to quickly make a left turn. Took it to the Mercedes dealer who though the backfire was the waste gate. Could not find any reason for the occasional hesitation on acceleration. So I sold it in September of 2018. For the OP, if the last digits of you VIN are 51527 you have the one I sold.

I replaced it with an electric Chevy Bolt EV. Love the acceleration, dependability, no gears to shift, no oil to change (or any other services to pay Mercedes prices for). We only have to rotate the tires, add windshield washer fluid and change the cabin filter). It even has a much lower cost per mile for fuel. Really miss the tight turning radius and attention the smart got from others.
 

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I have a 2016 Smart and occasionally have noticed the hesitation on acceleration and a backfire which I have been able to contribute to bad gas I carry a bottle of octane boost and when ever the problem shows itself on the next fill up I add to the gas tank and the problem goes away
 
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