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.

 

that would cause bad fuel economy poor acceleration.you may have a pluged catalytic converter which could cause your exhaust manifold to spring a leak . did they check your coverters to see if the are pluged.

 

If there was a leak in the rear bank, it could lean out the rear 02 sensor and cause your milage to drop, because the ECU could be making the AFR run richer to comensate.

However, it may be something else in that area, like the EGR tube, that comes off the rear of the engine. That could also effect mileage.

Unless you hit something, this should have developed slowly. It's also a pain to remove the rear manifold and put a new gasket on. But doable with professional tools and u-joints/extensions. Make sure you insist on OEM gaskets.

 

Where is the ERG tube? Can I get the picture of that?
Thanks.

 

this is from the back its not directly visible from the fron of the motor


heres what the complete assy looks like
hope this helps a little

BTW:this EGR is for sale PM me