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

Hi all,

we are mystified as to why my 370z is dumping fuel into the left bank (2,4,6) and then causing it to misfire. Short Term Fuel trim on Idle starts at about 10% and gradually over the space of 5 minutes climbs to 25% and then misfires, reset's back to 0% and then starts again ( 10 -14-10-12-16-14-20-22-20-24- 25). It's throwing the fault code p0300 and it also on two seperate occasions said misfire fault in cylinder 4 and then 2.


trying to figure out why it's doing this

What have we done so far

Via the TORQUE app we were able to monitor most things.

- O2 Sensors are fine
- Air Flow Sensors were swapped around and didn't make a change to the fuel trim dumping fuel
- We couldn't find any cracked or torn pipes.
- we ruled out coil packs as the code is across multiple cylinders and we know its dumping fuel so ignition is not going to cause it to dump further fuel.
- Timing is between 10 to 11 Degrees when idle.



Mods are

Stillen Gen3 Intakes
Titanium Amuse Exhaust ( After the Y pipe)
Berk High Flow Cats

All mods were installed 2 years ago, so its not like anything has been added new to the car since.


Any thoughts guys??

first you need to remove the fuel injectors to make sure that they aren't stuck open.

after that if they dont leak, id say ECU.

Just guessing but, since the whole bank is involved, I'd check the wiring to the injectors.

we are thinking it actually might be gaskets before the o2 sensor on the left exhaust Header. We haven't done a smoke test of any sort. But getting to injectors would be a monumental task. We are going to get under the car and check all gaskets and seals. Because it Chugs and misfires hard in the cold morning or when the car is cold, but starts to even out and the misfire dissipates once the car is warm etc. Maybe the metal expands and closes the gap, etc etc.

Your giving a % but not giving a + or -. if it is + then ignore leaking injector etc etc as the ECM is commanding an increase. If a - then it is trying to subract so have to look for ways of unwanted fuel, that would be leaking injector etc etc. if a + trim first thing I would maybe try is disconnect both MAF sensor to put into a default open loop mode and see what the a/f is measuring. If it sees it as super lean then possibly an exhaust leak drawing air in or a poor sensor/wiring. It's late I'll see if something else comes to mind.

I noticed a pattern of one bank running different than another when I started tuning my car. I think it has something to do with the stock non-parallel fuel rails. Never really figured out the cause. But over a pull there are variations in the two banks' AFRs. Sometimes as much as a full point. In UpRev, there is a table where you can adjust fuel trims per cylinder. I went through and added 1% to all the cylinders on that bank, I think I added to cyl 1, 3, and 5, and then dialed in the correct AFR from there. If you're on ECUtek, I'm not sure what they have in terms of adjustment, but if UpRev has it, I'd imagine ECUtek would have something similar.

Wiring would be unlikely in this case as they will all share the same power but will have individual grounds. Meaning you would have to short all three grounds to have them dump fuel like that (not impossible but unlikely). Also we still don't know if those are + or - percent numbers so is the PCM commanding more or less fuel that will make a very big difference it what it could be.

i belive for that youll get anotger code if it was gaskets.

I believe this is because of bank one intake is connected to the engine emission, but not bank 2. Get a catch can and throw a Y connection to both banks and you will see your A/F ratio even. After you remove the adjust. I think thats why, but it also could be a leaking gasket somewhere.

You wouldn't get any other code but a lean bank code. The system has no way to determine an exhaust leak pulling air in before the A/F sensor. It has to take it on faith that it is sealed and the A/F sensor will be seeing that raw air as a lean condition and then dump fuel. Same thing will happen if the intake gasket on that side is not sealing drawing in fresh air after MAF. The p0300 is a random misfire code, misfiring because it is flooding the cylinder.

From the op description I would be leaning towards a gasket leaking (intake or exhaust, more likely intake just because most cars are much more likely to have an intake leak than exhaust but not all, cracked Honda exhaust manifolds anyone?), the intake is extremely common on Chevy v8 with the ealier gaskets and will do the same thing, get warm enough to go into closed loop and then start dumping fuel possible misfires and then settle out as it gets fully warmed up.

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?

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.

Thanks Man much appreciated!, il try this today.

Yea your give always are the clearing adeptive and seeing short term peg + 25%. You can think of 25% as 100%, once it hits 25% it jumps to a different block in the long term table and keeps doing that until it can get to one that is rich enough to satisfy short term. S you are running extremely lean from initial base value. The reason it ran ok before is because the leak or lack of fuel came on gradually and the PCM was able to compensate, once you clear the adeptive now it is set to base map and will run like crap, same thing happens all the time to vw/Audi 1.8t and you'll find a nice little slit at the seem of the molded plastic PCV elbow. I really doubt you have a MAF issue because I'm fairly certain the PCM isn't even looking at them on initial cold start, and it definitely is not looking at the A/F sensors at initial cold start, so it should be running richer as it needs to be. So you either have a lack of fueling issue or a intake leak you aren't finding.

Did you never have a lean bank code at all?

Ever figure this out?