exhaust leak and gasmilage???

[GermanMuscle]

i was just wondering if having a leaking exhaust could decrease the gasmilage

[unkn0wndj]

I dont think it'll affect Gas Mileage but I may be wrong.

[Bruce Leroy]

I have an exhaust leak right now. Nothing too big, i just haven't had the time to try and fix it. But i think that my gas mileage may have gone down a bit, maybe like 40 - 50 miles a tank.

[GermanMuscle]

yea thats what i figured since i was told that you lose power with an exhaust leak aswell

[Benefit]

so if u dont have an exhaust , say...just downpipe then nothing...your getting bad mpg

[atl530i]

I have an exhaust leak right now. Nothing too big, i just haven't had the time to try and fix it. But i think that my gas mileage may have gone down a bit, maybe like 40 - 50 miles a tank.

40-50 miles a tank? I think I would be fixing that the same day it happened.

[Z U L8R]

having a leaky exhaust.......in your exhaust you have what is called OXYGEN SENSORS. they sense the amount of oxygen that's coming out of your engine after it burns fuel. they in part with other sensors communicate with the car's computer ( brain ). if the sensor senses too little oxygen it tells the computer the car is running rich and it reacts by giving less fuel to the choking engine. if the sensor senses too much oxygen to fuel (air/fuel ratio) then the computer will compensate by adding more fuel to the hungry engine so it won't run lean. if your car's exhaust is leaking then the sensor will pick up more oxygen in the exhaust than is really there thus making the car run richer thus robbing gas mileage.

can an exhaust leak hinder gas mileage? yes....is that YOUR problem perhaps part...... perhaps all.......

i'll teach you something too

obd2 (96 and up) cars have 2 oxygen sensors, some cars have more, but to keep it simple you have

THE MOTOR-----THE EXHAUST MANIFOLD----OXYGEN SENSOR 1---CATALYTIC CONVERTER---OXYGEN SENSOR 2------RESONATOR----MUFFLER

sensor 1 or pre cat or upstream whatever you call it, that sensor will fluctuate..think of a heartbeat machine at a hospital, it'll go way up and way down.

then the exhaust goes through the converter which is hot and burns more unburned fuel thus creating cleaner emissions ( lower Nitrous Oxide aka nox ) and as it is now cleaner it meets oxygen sensor 2

if the converter is doing it's job then sensor 2 won't fluctuate that that much, imagine the heartbeat of a dead patient.....

if the converter is bad then sensor 2 will have the same heartbeat as sensor 1 ( in voltage ) , they will basically mimick one another because inbetween the two sensors the converter is not converting. which at this point you will get a check engine light with a "CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD" code.

o2 sensors are a wonderful thing

[Z U L8R]

i am not saying you need or don't need o2 sensors, don't worry about o2 sensors for now, i'm saying fix your exhaust leak and see if that helps your gas mileage then go from there.

[Z U L8R]

most newer bmw's have 4 o2 sensors, factory recommended replacement is 100,000 mile service, they LIST out at $175 EACH...doesn't mean you have to pay that but don't put CRAP on your car either

[scttydb411]

every thing he said^^^if the exhuast leak is before the sensors. if it's towards the back it's not the issue and it's something else.

[falqon]

If somehow you have a exhaust leak before the o2 sensor, (which is pretty rare) then yeah, better get it fixed.

A hole in the exhaust after that should not be detrimental to MPG at all. Losing back pressure should cause highway MPG to go up at least in most imports. The reasoning is this, yes you might lose some torque, but you should gain HP. Back pressure helps low in the power band, but as the RPM's climb the restriction outweighs any benefits. I had a hole in my old fox body mustangs muffler for a couple months, MPG actually went up. A test pipe does not hurt MPG, I have never seen or heard that theory, and if that were true, then nobody would buy "hi-flow" cats.

Most cars that come off of the assembly line today suffer from too much backpressure, the reason is the catalytic converter. The stupid things rob you of mid-high end power and really hurt fuel economy. If the exhaust leak is after the cat, this whole thread is probably moot, that restriction will negate much of what a hole in your exhaust might do.

[GermanMuscle]

thx for all the great info. i have 2 cars that are leaking, a 90 integra which is the one why i asked since its going to be my DD soon, it leaks on the welds in the mid section of the piping i think there is even a small leak before the cat and then 2 after teh cat. the welds look really half ass and need to be redone since theyre leakingand the muffler is all messed up too

[1439/2000]

If somehow you have a exhaust leak before the o2 sensor, (which is pretty rare) then yeah, better get it fixed.

A hole in the exhaust after that should not be detrimental to MPG at all. Losing back pressure should cause highway MPG to go up at least in most imports. The reasoning is this, yes you might lose some torque, but you should gain HP. Back pressure helps low in the power band, but as the RPM's climb the restriction outweighs any benefits. I had a hole in my old fox body mustangs muffler for a couple months, MPG actually went up. A test pipe does not hurt MPG, I have never seen or heard that theory, and if that were true, then nobody would buy "hi-flow" cats.

Most cars that come off of the assembly line today suffer from too much backpressure, the reason is the catalytic converter. The stupid things rob you of mid-high end power and really hurt fuel economy. If the exhaust leak is after the cat, this whole thread is probably moot, that restriction will negate much of what a hole in your exhaust might do.

Not rare at all on a turbo car.