2002 NIssan Xterra 3.3L VG33E engine misfire P0300

I put the O2 connectors back to original position, here are the trims again:
at idle:
STFT B1 0.8
LTFT B1 9.5
STFT B2 -0.8
LTFT B2 -5
at 2500 rpm:
STFT B1 7.8
LTFT B1 9.4
STFT B2 -10.2
LTFT B2 -10.2

Then, i disconnected the brake booster vacuum hose, and here is what i got:
at idle:
STFT B1 25
LTFT B1 9.4
STFT B2 25
LTFT B2 -5.5

at 2500 rpm:
STFT B1 25
LTFT B1 9.5
STFT B2 -3.3
LTFT B2 -3.1

I think this proves the O2 sensors are good based on what you mentioned. But I can still swap them tommorow and check again.

Isn't bank 2 on the drivers side of the engine? If so, I can't unplug those fuel injectors on bank 2 since they are under the upper intake manifold.

I think Monde is right. with no other ussue but vacuum leak, both STFT & LTFT would go to high positive. Anyway, if you compare both Banks STFT, they reacted so similar, which makes me think both O2 sensors are good. That test allows me to think we are dealing with two separate issues here.

I think we have an injector leaking on bank 2. Why does an injector and not other fuel source? Because the uncontrolled fuel source is not affecting both Banks.

We could have also a fuel delivery issue which is affecting both Banks, but the fact we have an injector leaking does not allows us to realise bank 2 is being affected too. Anyway, those are just theories we need to prove.

To check injectors on bank 2 you can do a balance test (if available) or you can check all injectors at the same time.

mdce4: take a look at scannerdanner YouTube videos "how to identify and repair a leaking fuel pressure regulator (GM CPI system). Note: This test is only for engine off, you need to find out how to check intermitent stuck open injector.

guafa wrote: I think we have an injector leaking on bank 2. Why does an injector and not other fuel source? Because the uncontrolled fuel source is not affecting both Banks.

We could have also a fuel delivery issue which is affecting both Banks, but the fact we have an injector leaking does not allows us to realise bank 2 is being affected too. Anyway, those are just theories we need to prove.

Bank 2 gets worse at higher RPM which doesn't really fit those either of those theories. A leaking injector should have less effect as metered fuel increases. A fuel delivery issue should drive both banks leaner as fuel demand increases.

IMO valvetrain and plugged upstream cat both fit the symptoms. In cylinder transducer would be the easiest way to check for both. Since I doubt the OP has one here's a link to one of the DIY transducer threads.

www.scannerdanner.com/forum/diagnostic-t...nder-transducer.html

Thanks Matt, I was thinking about an injector which intermitently gets stuck open (plugged pintle or so)

Do you think is worthless a balance test?

The rich and lean banks look to be happening consistently based on the OPs scan data. Doesn't appear to be intermittent and a breathing problem seems to fit the symptoms better than fuel IMO.

That said the original P0300 complaint might not be related to the B1/B2 imbalance we've all gone off on a tangent chasing :lol: So there could also an injector issue causing the misfires.....

Ok, back before i had replaced injector, here was the balance test i did:

INJECTOR # | WIRE COLOR | START PRESSURE | END PRESSURE | OHMS READING
_____________________________________________________________________________________
1 wht/black 40 psig 26-27 psig 14.4
2 wht/blue 40 psig 26-27 psig 14.9
3 wht/red 40 psig 26-27 psig 14.3
4 wht/purple 40 psig 30-32 psig 148
5 wht/green 40 psig 26-27 psig 14
6 wht 40 psig 25-26 psig 14.2

after replacing injector #4, i did another test and they were all about the same pressure drop. I also replaced the fuel filter at this time, and double checked fuel pressure it was within specs.


i physically swapped the O2 sensors, just to be sure. Here are the readings:
idle:
STFT B1: 0.8
LTFT B1: 7.8
STFT B2: 0.8
LTFT B2: -8.6

2500 RPM:
STFT B1: 13.3
LTFT B1: 9.4
STFT B2: -14.8
LTFT B2: -10.2

they look the same as before i did the swap.
I'm going to do an exhaust backpressure test, i'll let you know when i get the results of that.

Just a quick question, I've finally got an in cylinder pressure transducer that I can use. I was going to do a in cylinder running test with this installed in a cylinder on bank 2. The problem is I won't be able to disconnect the fuel injector for this since its under the intake manifold.

Is it ok to run the engine but not disconnect the fuel injector? I just want to make sure I don't flood or damage something while the engine is running.

mdce4 wrote: Is it ok to run the engine but not disconnect the fuel injector? I just want to make sure I don't flood or damage something while the engine is running.

It'll be OK enough. I wouldn't run it that way forever, just long enough to get a crank, a steady idle and a WOT snap.

Here are some trends for the in cylinder pressure transducer engine running test, snap throttle. I attached a trend for bank 1 cylinder 3 (looks good to me?), and a trend for bank 2 cylinder 4 (bad side).

I have no experience interpreting these kind of trends, but even i can tell that Bank 2 looks horrible. I also tested another cylinder on bank 2 and it looked just as bad.

So, i removed the O2 sensor on B2 and connected a gauge for exhaust back pressure test, and on snap throttle, the gauge was pegging out at 15 psig. I did the same for B1 exhaust pressure, and the gauge stayed at 0 the entire time.

So, i guess i'm dealing with a plugged cat on B2, but is the misfire caused by this blockage on B2, or is there still another issue going on?

The catalytic converter was restricted. I removed it. While I'm waiting for the new part to come in, can i run the engine with bank 2 exhaust open to atmosphere? It would just be emptying into the engine bay, and i would leave the hood open. I want to do this to see if the misfire is still there. I just don't want to damage anything unintentionally.