370z Dumping Fuel into Cylinder 2,4,6.. WHY??!?

Z34Life

So this is getting stranger and stranger,

Had the exhaust checked out by my buddy who is a BMW mechanic but owned a 370z so knows a thing or two about both areas. Nothing was out of the ordinary for him that would cause a misfire in his opinion. Majority of exhaust shops i explained this too said " never heard of a car having a misfire from an exhaust leak after the 02 sensors. you would ran either rich or lean but not have multiple cylinder misfire."

The problem is very intermittent, the last two days we decided to reset the long fuel trims and at first it was struggling, putting in 25% + into short fuel trims on both banks. It then came down levelled out and Long fuel trims returned to 9.4 to 10.4 on both banks, and Short fuel trims were between -3 to +6 on both trims.I could hear a slight misfire if you listened carefully but it didn't miss a beat? Ran well!

then this morning went to start it and it started like a truck on 2 cylinders! it was mis firing like crazy, struggling to hold RPM and was just wasn't happy at all. Short trim was now back to 25% + ( constant) on both banks and long trim is on 10.4+ to 13.5+.

it then threw the fault code of misfire in cylinder 3 , so its not just left bank anymore...

we are so confused on why this is happening. We re checked intakes, no leaks no tears, PCV valves are all good. and the car isn't throwing fault codes for o2 sensors. HOWEVER, i noticed this morning (potentially once or twice before) the o2 sensor and catalyst status are "incomplete" via the torque app. Now I know you need t drive the car to allow it to run its cycle to allow it to complete again. However it is now staying as Incomplete.

Thoughts?

Jhill

Ah this is making more sense. You said it is dumping fuel and I took it in faith that it is. But I forgot to ask, is this truly running rich? Are the plugs fouled out? That's how rich it would have to be to have misfires. My bet it they are not. My bet is you are not running rich but are running extremely lean and it is trying to dump fuel. Issues that cause this. Vacuum leak after MAF, failed MAF, or my bet after reading this, failing fuel pump or fuel starvation (filter, linked line etc). Your cold start running like crap re affirms this because cars need to run rich when cold.

Get a fuel pressure reading, and do a volume test, I bet it's low since you already checked for the vacuum leaks. I know the fuel pressure doesn't have a schreader port so that suck, before you go to that trouble, disconnect both MAF and see if there is any change, just to rule them out I'll bet you have no change.