will an exhaust leak give you shitty gas mileage?

[suprana1990]

hi everyone

my suppy is 5spd NA and i get like 13mpg city driving and around 17mpg high.
lets just say i didn't break 200miles for a full tank.

i changed the plugs n wires, timing is good.
gas i getting really expensive and i would like to know if an exhaust leak on the exhaust manifold will give me such crappy miles per gallon.
:1zhelp:

 

[IJ.]

Check the 02 sensor.

 

[MK3Brent]

hi everyone

i would like to know if an exhaust leak on the exhaust manifold will give me such crappy miles per gallon.
:1zhelp:

No.

 

[RacerXJ220]

It can cause you to loose torque, and you'll have to give it more gas than normal, hence miles per gallon goes down.

 

[jetjock]

Any codes?

If it's located upstream of the O2 sensor it certainly would. Otherwise no.

 

[Nick M]

hi everyone

my suppy is 5spd NA and i get like 13mpg city driving and around 17mpg high.
lets just say i didn't break 200miles for a full tank.

i changed the plugs n wires, timing is good.
gas i getting really expensive and i would like to know if an exhaust leak on the exhaust manifold will give me such crappy miles per gallon.
:1zhelp:

Absolutely yes. The false air leak creates a lean voltage signal, and the ECU goes richer trying to correct it.

 

[mk3some]

Absolutely yes. The false air leak creates a lean voltage signal, and the ECU goes richer trying to correct it.

right on man, that's absolutely correct. u will lose fuel economy with an exhaust leak def....

 

[Nick M]

Well he said at the exhaust manifold. A hole in your muffler won't do shit. As IJ said, check the oxygen sensor voltage. It should switch, but lean it will stay under 450 mv.

 

[Joel W.]

Also: Any exhaust leak at the manifold gasket could cause the turbo to spool slower causing poor mileage. IMO

http://groundsky.co.nz/techinfo/TSRM/05_TC.pdf Page TC-5

 

[jetjock]

I missed the "manifold" part as I was responding to the thread title. My point stills stand though: any leak upstream of the O2 sensor will cause the condition Nick pointed out. It may even be bad enough to drive the sensor all the way lean. In any case, the ecu will add more fuel to compensate.

Leaks downstream of the sensor won't do squat to the A/F loop but will cause higher than normal O2 readings on a gas analyzer. Since oxygen is a window past the cat this can be a hassle when troubleshooting emission problems.

 

[Joel W.]

I got my TCCS today JJ. Interesting read. Thanks for the link..

 

[jetjock]

Shhh....or everybody will want one . Any questions, ask.

Hey, do you still have EGR on your car? PM me if you do.

 

[Joel W.]

I just saw he was N/A so disreguard what I said about turbo spool.

My bad...

 

[Fastway135]

How about a leak under the car in a catback piping? (such as around the cat area where the bolts are.) Can this affect gas mileage to?

 

[jetjock]

No. But it'll likely effect emissions if it's before or around the cat. To work the cat must be fed a composition of exhaust gases that only occur in a very narow range of engine control. That's the reason the O2 sensor is there to begin with. It's why any engine that's not running in control will render the cat not only disfunctional but in most cases destroy it. A leak where you say won't ruin it though, it'll only hamper it's operation.

 

[suprana1990]

first off thanks for everyone's reply

there is no code, i changed my o2 sensor also.
what color is the o2 suppose to look like if it is running lean or rich?
i think the last time i checked it was ashy white.
i just filled up my tank this afternoon and with this prob. 50bucks work of gas for only 215miles :1zhelp:

i think the problem could be the exhaust manifold connecting to the collector pipe going down to the cat.
but will be taking it apart after my finals with school to see if that is the problem. just 3 more days and i am free!

 

[mrnickleye]

It can cause you to loose torque, and you'll have to give it more gas than normal, hence miles per gallon goes down.

Ok, ok, I calmed down and erased my first responce !! So....

I think he's talking about an exhaust gasket leak, which will not be enough to cause the responce you provided to become reality.

Now for some areas to check. Like said above...02 sensor.

Also, check all vacuum lines, intake gaskets for leaks. Intake plumbing. Fuel pressure regulator. (if vacuum line is off, more fuel use).

Are you getting timing advance???

TPS, AFM, ECU coolant temp sensor. Knock sensor (will retard timing).
Leaking injectors. ???

I, along with many others, get about 15 city / 22 hwy.:icon_evil

Can't seem to keep my foot out of it .:biglaugh:

 

[Fastway135]

first off thanks for everyone's reply

there is no code, i changed my o2 sensor also.
what color is the o2 suppose to look like if it is running lean or rich?
i think the last time i checked it was ashy white.
i just filled up my tank this afternoon and with this prob. 50bucks work of gas for only 215miles :1zhelp:

Just curious but what is the average miles an mk3 turbo and na with few/no mods should get for a full tank of gas?

 

[Joel W.]

I got 17-21mpg before mods, and 21-25mpg after mods.. I equate it to better flow through the motor.

 

[mrnickleye]

I always fill my tank, and I always use the trip OD to check milage. Over the years, this has saved me some $$$ because I caught some 'misfiring' problems early.:icon_razz

Before the mods, I was getting 17 city / 24 hwy. Now 15 city / 22 hwy. I figure its because I like the extra power, and use it around town.:biglaugh:

And in my earlier post, I said a leak at the manifold in itself would not cause a loss of fuel economy. I was thinking a small, ticking leak, like a loose bolt, or beginnings of a leak. I wasn't thinking of a big fat leak, as a blown flange gasket. :nono:

I've always changed a gasket at the first signs of leaking (ticking sound), cause if you don't, you can cause yourself more problems. As apparently he has, with a large leak, which will draw outside air into the exhaust stream with the pulsations of the exhaust.