P0300 Random Misfire - No Idea what’s Next - Second Generation Nissan Xterra Forums (2005+)
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post #1 of 14 (permalink) Old 01-05-2019, 09:39 PM Thread Starter
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P0300 Random Misfire - No Idea what’s Next

To start off I have new plugs, new coils and new fuel pump.

I am getting a random misfire code P0300 and nothing else. She has absolutely no power.

I checked the resistance on HO2 sensors and camshaft sensors. All checks out okay.

Watching O2 sensors on the scanner I see Bank 1 (pax side) averages substantially richer than bank 2 (drivers side). Replaced upstream O2 sensor on pax side just to see if it worked and still no luck.

I have checked for intake leaks using starter fluid and sprayed the entire engine bay and underneath the aluminum intake plenum under the plastic one. No change in rpms on the scanner.

I didn’t bother with crank sensor because I’m only running rich on the one side. My exhaust is stock just did a muffler delete.

I’m at a complete loss as to what to do next. Anyone have any ideas? Would be appreciated, thanks
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post #2 of 14 (permalink) Old 01-05-2019, 09:54 PM
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Originally Posted by 07offroadx View Post
To start off I have new plugs, new coils and new fuel pump.

I am getting a random misfire code P0300 and nothing else. She has absolutely no power.

I checked the resistance on HO2 sensors and camshaft sensors. All checks out okay.

Watching O2 sensors on the scanner I see Bank 1 (pax side) averages substantially richer than bank 2 (drivers side). Replaced upstream O2 sensor on pax side just to see if it worked and still no luck.

I have checked for intake leaks using starter fluid and sprayed the entire engine bay and underneath the aluminum intake plenum under the plastic one. No change in rpms on the scanner.

I didnít bother with crank sensor because Iím only running rich on the one side. My exhaust is stock just did a muffler delete.

Iím at a complete loss as to what to do next. Anyone have any ideas? Would be appreciated, thanks

The lack of power you describe sounds a lot like some of the guys here that have had one of the catalytic convertors break up inside and clog the exhaust pipe. The convertor dust can also be sucked into some of the cylinders and it scours the cylinder walls causing a lot of oil to leak by the piston rings...basically the engine can need replacing. Before anything else I'd pull of the secondary convertor pipes and get a look at the primaries to check if either one has broken up.


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post #3 of 14 (permalink) Old 01-05-2019, 11:24 PM
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Oh man this sounds ominous


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post #4 of 14 (permalink) Old 01-06-2019, 12:30 AM Thread Starter
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[/quote]


The lack of power you describe sounds a lot like some of the guys here that have had one of the catalytic convertors break up inside and clog the exhaust pipe. The convertor dust can also be sucked into some of the cylinders and it scours the cylinder walls causing a lot of oil to leak by the piston rings...basically the engine can need replacing. Before anything else I'd pull of the secondary convertor pipes and get a look at the primaries to check if either one has broken up.[/QUOTE]

Well checked compression. Cylinder 6 is at 90psi. Threw some oil in there and came all the way up to 190. So you may be correct and now my rings are shot. 130k miles.

She’s been really good to me since 2010. Mostly minor issues.

But looks like I’m either doing a rebuild or a swap. Not sure what’s the best option here, will have to do some research.

Down to one vehicle now, good thing it’s almost tax season because I wanted to get a daily driver anyway.
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post #5 of 14 (permalink) Old 01-06-2019, 08:35 AM
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She’s been really good to me since 2010. Mostly minor issues.

But looks like I’m either doing a rebuild or a swap. Not sure what’s the best option here, will have to do some research.

Down to one vehicle now, good thing it’s almost tax season because I wanted to get a daily driver anyway.
Yes most likely cats. Your engine might be fine - its not automatic that it hurts the engine. Some do, some don't. You will need to replace or gut the cats to find out. I would pull the cats, gut them all, and put them back on. If it runs fine and doesn't burn oil - your engine is fine, albeit you will still have a CEL light. At that point you can replace the cats properly.
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post #6 of 14 (permalink) Old 01-06-2019, 10:50 AM
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P0300 Random Misfire - No Idea what’s next

Could definitely be cats which is serious like others said, but did this start before you replaced plugs, coils and fuel pump or after? I would be suspicious of the work I just did if it showed up right after.
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post #7 of 14 (permalink) Old 01-06-2019, 05:27 PM
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Plugged cats.

If you are already down on compression itís probably too late. What was the compression on the other cylinders?

I put a new engine in mine.
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post #8 of 14 (permalink) Old 01-06-2019, 08:25 PM
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The lack of power you describe sounds a lot like some of the guys here that have had one of the catalytic convertors break up inside and clog the exhaust pipe. The convertor dust can also be sucked into some of the cylinders and it scours the cylinder walls causing a lot of oil to leak by the piston rings...basically the engine can need replacing. Before anything else I'd pull of the secondary convertor pipes and get a look at the primaries to check if either one has broken up.[/QUOTE]

Well checked compression. Cylinder 6 is at 90psi. Threw some oil in there and came all the way up to 190. So you may be correct and now my rings are shot. 130k miles.

Sheís been really good to me since 2010. Mostly minor issues.

But looks like Iím either doing a rebuild or a swap. Not sure whatís the best option here, will have to do some research.

Down to one vehicle now, good thing itís almost tax season because I wanted to get a daily driver anyway.[/QUOTE]


Yeah I think you've mostly confirmed it with the compression test, at this point you could pull the cat just to completely confirm it but I think it's safe to say it's probably broken up. @jsexton had that same thing happen to his X and he ended up swapping the engine I think.


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post #9 of 14 (permalink) Old 04-27-2019, 06:51 PM Thread Starter
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Originally Posted by General_Tarfun View Post
The lack of power you describe sounds a lot like some of the guys here that have had one of the catalytic convertors break up inside and clog the exhaust pipe. The convertor dust can also be sucked into some of the cylinders and it scours the cylinder walls causing a lot of oil to leak by the piston rings...basically the engine can need replacing. Before anything else I'd pull of the secondary convertor pipes and get a look at the primaries to check if either one has broken up.
Well checked compression. Cylinder 6 is at 90psi. Threw some oil in there and came all the way up to 190. So you may be correct and now my rings are shot. 130k miles.

Sheís been really good to me since 2010. Mostly minor issues.

But looks like Iím either doing a rebuild or a swap. Not sure whatís the best option here, will have to do some research.

Down to one vehicle now, good thing itís almost tax season because I wanted to get a daily driver anyway.[/QUOTE]


Yeah I think you've mostly confirmed it with the compression test, at this point you could pull the cat just to completely confirm it but I think it's safe to say it's probably broken up. @jsexton had that same thing happen to his X and he ended up swapping the engine I think.[/QUOTE]

I am having a lot of people tell me it could be the computer at fault. I believe, but could be wrong, that I have had low compression in that cylinder for a while. This would explain the rich exhaust smell and 11-12mpg that I have had for a while. I don't think low compression in one cylinder would cause a random multiple misfire code. I haven't touched the vehicle since I discovered the low compression. Just been sitting now while I save up money and decide what to do. If anyone has suggestions as what else to try before I do a new engine/rebuild the current one I am open to anything. I know it still needs it but I dont want to do all that work and it still be something else because then I will just want to burn the damn thing down.
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post #10 of 14 (permalink) Old 04-27-2019, 11:13 PM
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Have you had a chance to pull the cats yet? I'd want to look at those before making any decisions to see if they were broken up inside.
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