The rear exhaust leaking issue.

[Ryan Heo]

Hi.I have 96 I30 which is 133k on it. It has terrible gas mileage like 15~16 miles/gal(premium). All of the O2 sensors, knock sensor, filters were replaced within 4 months. Also wheel alignment was done. However it is still bad gas mileage. I went to check the engine to the shop.

They told me the rear exhaust manifold is leaking, so that gives wrong information to O2 sensors. It could cause the bad gas mileage.

Is it possible? Does the exhaust have to be replaced for restoring normal gas mileage?

Thanks.

[MinisterofDOOM]

It's definitely possible.

You may not need to actually replace any exhaust components. It depends on where and how it is leaking. You may just need to replace manifold studs.It does take a lot of labor to get to the rear exhaust manifold, though.

[Ryan Heo]

What is the exhaust studs? Can I have any picture or diagram of that from a repair manual?

Thanks.

[MinisterofDOOM]

They're the bolts that hold the manifold to the engine.

[Sentientbydesign]

I know that this issued caused MPG and power issues on my wife's 93 celica. It would barely go up hills and was getting about the same MPG as my I30.

Her dad replaced the exhause manifold and immediately power and MPG were improved.

[Ryan Heo]

Shoul I buy OEM manifold gasket even though I ordered an exhaust manifold included a gasket and studs at Autozone?

Thanks.