Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

2002 NIssan Xterra 3.3L VG33E engine misfire P0300

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3 years 7 months ago #42107 by mdce4
Hi, I'm trying to determine the cause of a misfire on this Xterra, 2002 V6, 3.3L VG33E engine. It has an engine misfire code P0300.

I have already replaced the spark plugs, spark plug wires, and a fuel injector that had a high resistance reading. I have not tried to replace the distributor cap and rotor yet.

Some screenshots from my scope is attached. This is from one of the plug wires, but all 6 of them have a similar behavior. I can see that there is an ignition waveform buried in there, but there is a ton of spiking and really bad looking waveforms constantly coming in. Is this an indication of anything that you know of?

I was using a Hantek scope with an HT25 COP probe and holding it next to the plug wires. I'll be glad to get more screenshots if it would help. I used this same method with another truck that had Coil on plug igntion and it gave a good clean looking ignition waveform, so i don't think its a problem with my test equipment.

I'm just a guy trying to work on his own vehicle and i'll admit i still have a lot to learn, so i may be something simple that i'm missing.

Let me know if you've got any ideas.

Thanks

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3 years 7 months ago - 3 years 7 months ago #42109 by guafa
Hi Mdce4,

Are you snapping the throttle in those pictures?

Do you have frezze frame data? I mean, what were rpms when DTC was set?

Do you have fuel trims, IAC position, Map and others?

Can you describe which cylinder was scope and what are those traces?

The first picture looks like "No fuel misfire" but only if that was on snap throttle.
Last edit: 3 years 7 months ago by guafa.

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3 years 7 months ago #42116 by mdce4
Those pictures were at idle. It was on cylinder #4, but the others are similar.

I attached some more pictures at other engine speeds.

When the DTC was set, the engine speed was idle, at 775 rpm.

STFT B1: 0.8%
LTFT B1: 9.4%
STFT B2: 1.6%
LTFT B2: -6.3%

MAF 0.78 lb/min
TPS 0%
IAT 144 F

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3 years 7 months ago #42117 by Donut
To get a good idea of where to start check the fuel trim numbers, long term and short term. Doesn't hurt to see how the O2 sensors are working. If you don't have a scanner that has a graphing option for PIDs then you can use your scope instead, and Nissan was nice enough to put the connectors for the O2 sensors on top of the passenger valve cover. Signal wire should be pin 2, which should be the center wire and a solid black for bank 1 and green for bank 2.

"Don't ever say 'easy' until the check clears."

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3 years 7 months ago #42118 by Donut
Hood open or closed for the last reading? IAT seems high, and the MAF reading is a little high at idle, assuming no loads are on anyways.

What do the trims do at 3k RPM?

"Don't ever say 'easy' until the check clears."

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3 years 7 months ago #42139 by mdce4
The O2 sensors seem to be switching, i got some screenshots from those connectors you mentioned.

Here are the fuel trims at 3000 rpm:
STFT B1: 12.5%
LTFT B1: 9.4%
STFT B2: -13.1%
LTFT B2: -10.2%
IAT: 124F
TPS: 6.3%
MAF 2.95 lb/min
Spark adv: 43 deg

the hood was open during these readings.
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3 years 7 months ago #42145 by Tutti57
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

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3 years 7 months ago #42152 by Tyler
Agree with Tutti57, not loving those trims. :( I'd be tempted to do a relative compression test next.

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3 years 7 months ago #42169 by mdce4
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.
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3 years 7 months ago #42179 by Donut
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?

"Don't ever say 'easy' until the check clears."

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3 years 7 months ago #42203 by guafa
Take a look at scannerdanner YouTube video "secondary ignition waveforms (common faults)" for interpretation of your pictures on a snap throttle.

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3 years 7 months ago #42225 by mdce4
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.
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3 years 7 months ago #42238 by Matt T

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.

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3 years 7 months ago #42240 by guafa
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?

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3 years 7 months ago #42314 by mdce4
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
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3 years 7 months ago #42315 by Donut
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.

"Don't ever say 'easy' until the check clears."
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3 years 7 months ago - 3 years 7 months ago #42320 by guafa
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?
Last edit: 3 years 7 months ago by guafa.

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3 years 7 months ago #42326 by mdce4
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.)
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3 years 7 months ago - 3 years 7 months ago #42329 by guafa
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).
Last edit: 3 years 7 months ago by guafa.

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3 years 7 months ago #42331 by guafa
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.
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