ryan_89_mustang

What can cause a lean condition on one bank. When I ran Koer I got a drivers side lean code, I also have **** poor gas mileage. I think it is truly running lean because that header does seem to get a lot hotter then the pass. side one. I was thinking vacuum leak but that should reflect on both banks right? The car is SD by the way and stock engine. Any ideas? Thanks

Joel5.0

Exhaust leak, vacuum leak, defective O2 sensor (reading lean causing the EEC to overcompensate for fuel trim), faulty wiring, faulty ECM, clogged injector(s)..........

ryan_89_mustang

Turns out I had an exhaust leak one of the bolts on the header to midpipe I took off with my fingers. This was on the drivers side as well. Could that cause very poor gas mileage??

droptop302

Heder bolt noway. I read something on this forum today that said when you put headers on w/t x or h you might run lean not sure if its true.

Joel5.0

An exhaust leak will cause fresh air to be injected into the exhaust stream, it will cause the O2 to read "lean" by error, and will trigger the EEC to add fuel for that bank only based on the "bad" information from the O2.

droptop302

Header bolt give you poor gas mileage hum?

ryan_89_mustang

I hope that is why my mileage is so bad. I highly doubt a loose bolt is giving me less then 10mpg in town, I am getting a couple o2's tomorrow since there on sale at crappy tire I have no idea how old mine are.

will

I'm gonna put new header bolts in all my cars now Seriousally though you could have a dvr lower intake gasket bad,malfunctioning injector, o2 sensor... if it's bank specific

Foxbodyforever

this is the exact same thing i went through last week, lean code, and exhaust leak at the header on both side, paid $150 to get the holes fixed and my mileage went from 13mpg to 22.3mpg (highway)

ryan_89_mustang

It really went up that much???