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Exhaust leak could decrease your fuel economy?

 

I know my grandpa's truck before we started restoring it had a horrible exhaust leak. Ran awful and got horrible mileage cause you had to keep your foot on it to keep it running. We redid the whole exhaust from the manifolds back. Runs like new and doesn't eat as much fuel because you don't have to keep your foot on it.

I guess it depends upon how much it leaks. If its alot before the o2 sensors, I would think it would throw things off.

 

Depending where the leak is it can definitely cause fuel economy and other issues... if it's before the 02 sensors they won't read correctly.

 

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Its before the last big cat ( which is a o2 after that). Its not huge but you can hear it standing outside truck only. Its the flange. Jus wondering cuz i used to get 18 19 but now i get 16 17

 

1-2 mpg could just be the winter blend fuel you are running now. I always get a little better mileage when the gas stations switch back to the summer blend.
A minor leak like that should not throw off the mileage much at all.

 

Wish I still had the link to the page , but years ago an engineer for an auto company explained about exhaust system design.
IIRC the exhaust travels downstream in pulses. As each pulse moves it creates a scavenging effect ( a vacuum behind the pulse) which helps pull the next pulse behind it.
If you look at a set of headers , each tube is a different length on "tuned" headers.This is so the pulses travel in an orderly fashion down the exhaust.
In a manifold type exhaust the ports in the manifolds are different sizes (diameters) to get the same effect.
A hole in the pipe after the headers or manifold reduces the scavenging effect , making the system, well , pile up on itself.One pulse slamming into part of another.
Hope this makes sense.

 

Around when do they switch to winter blend?

and yes actually that explains alot. Im gunna get that fixed.id do it myself but the headers come n meet at strange angles preventing me from straight piping or meeting to a new cat.

 

usually when it starts getting cold.
The winter blend comes from the old days of metal gas tanks, so that no water could get in the tank and mess up your car.