Really bad mileage diagnostic

[SiGmA_X]

Cross post from M42 club.

I just finished up a motor replacement in my gf's 318i and its getting horrid mileage. ~17mpg over 5 tanks, mpg=miles/gallons of course. The car is not entirely smooth at idle. Nearly, but not fully. I should add - I had the connector plugged in (disassembled 2yrs ago, forgot it was unplugged..) by the relay's, since unplugging that, you can now start and drive away vs before you'd have to let it warm up to drive. But its still not so great at all due to MPG and idle.

New parts:
*All timing chain components - M20 fly so used an indicator + cam blocks to set timing
*COP Conversion (new coils)
*Plugs
*O2
*Air filter
*Dyno oil (first oil change on new to us motor, will go to synthetic shortly)
*Deleted TB heater BS

Unrelated:
*All gaskets minus HG
*WP/Tstat
*M20 clutch/fly (Maybe cause of issues?)
*Compression is all even at 220psi/cyl

I scoped all sensors, everything looked good - The O2 was a bit lazy at around 800ms so I replaced it, but the new one is not really any better.... Weird its not <500ms like normal.. And nor is the MPG. So looks like I have an almost-new O2 FS...

Any input would rock, I'm getting fed up with this 4 cylinder lol. Shoulda done an M50 swap, better MPG and more power/reliability/cheaper!!

Thanks much
Roman

[vpilarrt]

I'd look for a vacuum leak in the intake hoses. Also check your cam timing again. There is an arrow on the front of the oil filter housing that should line up with a mark on the front pulley/damper.

I'm interested in your O2 sensor if you decide to sell it.

[immajackuup]

shitty injectors, get mustang injectors, you'll see 30 mpg and up.

[StereoInstaller1]

Roman, my first thought was likely something with the cam timing, then leaky injectors.

I got nothing for ya, sorry.

LF