Can a exhaust leak hurt performance and/or gas mileage?

[98FWDSM]

ok, i had my megan racing DP put on and i had it welded to a 3 inch hi flo cat and the welds must have popped because now it is louder and in the mornings when it is cold and just sittin idling then you can see the smoke coming from directly underneath the car. I have also noticed a considerable drop in gas mileage too....although it is probably time to change my plugs too. So....do you think that this leak is why i am losing so much gas mileage?

Thanks

 

[dlh1999]

I would imagine it'd depend on how big of a leak you're talking about. Generally, having no back pressure could cause at least some decrease in gas mileage, but you'd be talking about some good size leaks for that to happen. So to answer your question, it could be causing lower gas mileage assuming you have a major leak...otherwise, maybe it's time to change filters, plugs, etc.

 

[Venum]

The first thing to do is get under the car and look at the weld to see if it did, in fact, come apart. If so, how much? If it's large enough of a leak then you would lose power (like what dlh1999 said).

Also, how big was the drop in gas milage? You said considerable, but that's kind of vague. Get a tune up, plugs, etc. Also, my gas milage went back up after I flushed the radiator fluid, so try that too.

One more thing, have you been driving any different? For example, less considerably? Flooring it a lot more and that such...

 

[eclipx]

if the leak is bad enough, it might screw with your O2. the 02 will probably think there isnt enough airflow coming through the exhuast, and you could be running rich, meaning less gas mileage. in general, leaks anywhere arnt a good thing.