2002 NIssan Xterra 3.3L VG33E engine misfire P0300

Seeing opposite fuel trims on the banks always makes me think of timing, sticking vvt solenoid (which I don't think these have?), and mixed up o2 sensor wiring. Could any of these be your issue? Recent repairs maybe?

Nissan Technician

Agree with Tutti57, not loving those trims. I'd be tempted to do a relative compression test next.

I double checked it, and the O2 sensor wiring seems to be correct. It doesn't appear to have a VVT solenoid, that i know of.

I did a relative compression test, see the picture. It seems ok to me, but let me know what you think.

Can the timing be checked with a scope? I don't have a timing light.

Also tried doing a snap throttle test of the ignition, but I don't know if this picture is of any use or not.

Going from the service manual it doesn't look like these have any variable valve adjustments, just solid cam sprockets.

You can check timing with a scope, and on these the cam sensor is in the distributor so it's up front and easy to get to. The crank sensor is buried in back, so less fun there.

I can't remember if it's a pain to get the upper timing covers off to check the timing on the cams, but that may be the most effective way to check timing in this case.

Did it run any differently after you replaced the plugs and fuel injector?

Take a look at scannerdanner YouTube video "secondary ignition waveforms (common faults)" for interpretation of your pictures on a snap throttle.

I saw the video, but it doesn't say anything about if you can't get a good signal in the first place. On my signals, I seem to be getting a lot of interference from something. Maybe I'm doing something wrong. I couldn't figure out how to get the parade of all the cylinders together since the ignition coil and power transistor are located inside the distributor housing. I attached a drawing of ignition system, where should i connect my scope for this?

Donut, when i replaced the injector and the plugs and wires, it ran a little better at first, but then it started getting the misfire again. I'm still trying to figure out how to check the cam and crank sensors, i'll let you know when i get a trend of that.

mdce4 wrote: I saw the video, but it doesn't say anything about if you can't get a good signal in the first place. On my signals, I seem to be getting a lot of interference from something. Maybe I'm doing something wrong. I couldn't figure out how to get the parade of all the cylinders together since the ignition coil and power transistor are located inside the distributor housing. I attached a drawing of ignition system, where should i connect my scope for this?

Moving your trigger higher so it only triggers on the firing kV of the lead you're on should help. That and separating the lead you're 'scoping away from the other leads helps with noise. That said you aren't going to get a secondary parade from that vehicle. You'll have to test each plug wire individually.

Looks like you might be able to get a primary voltage parade from the IGNCK wire on coil side of the resistor. That's if you've got a 20:1 attenuator.

About how to check crank/cam. An alternative test here (because you are not trying to check sensor integrity but mechanical sync). use relative compression test (one trace tracking humps and valleys current. Another trace synchronizing ignition). knowing that compression is Good in all cylinders, you need to figure out ignition is in the rigth place (in both Banks).

Facts until now:
Code was set at normal temp operation and idling (no gaskets issue)
The more rpm you have, the more negative bank 2 goes and more positive bank 1 goes (bank 2 leading fuel control issue, bank 1 leading fuel delivery issue)
Fuel misfire neither ignition misfire, cause negative fuel trims (there is always more air detected by O2 sensors than expected)

Is one of the upstream sensors lying? what about swapping upstream O2 sensors?

I did a relative compression along with IGN signal. The picture is attached. Can you tell from this if the ignition is occurring in the right place?

I was able to get a trend of the cam and crank signals. They match what's in the service manual for idle and also at 2000 rpm. But this still doesn't answer the question for me about timing is correct or not.

The amp peak value on primary side of coil was not the same for all cylinders, does this make a difference?

Here are the readings after swapping the upstream O2 sensors:
At idle:
STFT B1 -17.2
LTFT B1 9.4
STFT B2 12.5
LTFT B2 -2.3

At 2500 rpm:
STFT B1 -25
LTFT B1 9.4
STFT B2 25
LTFT B2 -10.2

How new are those oxygen sensors? Trim readings are completely opposite now. If nothing else was changed between readings I'd be wary of the O2 sensors.

Your ignition timing looks alright. Considering Your compression doesn't have big dropouts and your spark appears to be near where it should be it doesn't look like your mechanical timing is off any.

First picture is a Little zoom out to 100% assure, but Ignition seems to be on time. Also you checked crank/cam correlation as you mentioned (which unless you have a swapped coil, tells you that PCM has to fire on time). F.Y.I check scannerdanner YouTube video "how to check for a jumped timing chain or belt" (from 4:30). I wouldn't worry about timing anymore.

As Donut mentioned. If nothing else changed, i would call for new O2 sensors (because both are reacting in the same way no matter where they are).

Second picture is for voltage (Green trace) and current (violet trace) at ignition control wire? Same question about blue trace in first picture. Is it voltaje or current trace?

I may have given you incorrect data on those O2 sensors. All i did was swap the connectors between the two sensors, I didn't actually remove either of them from the exhaust. So, I may not have proved anything there yet. I'm thinking i'll have to do this again. The problem is that the cables on the sensors are different lengths, so only one of them will reach, unless i make up some kind of jumper for the shorter one.

These are original O2 sensors as far as i know.

I zoomed in a little more for the compression test. The IGN signal (light blue) is voltage with an amplitude of about 4V.
On the other picture, the green was voltage (IGN control wire), and the purple was amps (blue wire #8 between resistor and ignition coil/transistor.)

Ignition is no time (the charge of coil is ending right at the top of the hump (end of compression stroke)).

About O2 sensors, you have proved that both circuit integrity are fine.

For O2 sensor test, you don´t need to move any of the connectors from where they live. Just unplug connectors, unbolt the sensors and swap them.

Edit: Do you mean sensor wire? ok. yes then. you have to extend wires (be careful).

Ok, we cannot forget we are looking for direction and swapping O2 sensors is just a test to know whether or not sensors are lying. let´s asume O2 sensors are to complicated for swapping.

If you make a vacuum leak PCM Will respond adding fuel because you create a lean condition. If O2 sensors are ok, both banks STFT should go more positive (bank 2 less negative).

With engine running, also you can unplug injectors one by one on bank 2 (the rich one) and keep an eye on STFT. if there is a leaking injector, you should see a noticeable change.

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.