Someone please help! 08 Pathfinder engine issue (New member also)

[BrittanyTN]

Hey yall, first off, I'm a new member on here, so I just want to say thank you in advance for any help or advice on my issue I'm about to describe.
So I have an '08 Nissan pathfinder 4WD, about 3 days ago my service engine soon light came on, and nothing was really going on yet, then yesterday my SES light started flashing only when I would get above 2 RPM, then it would just stay illuminated when under 2rpm. It also has a pretty noticeable rough idle, and now today I noticed a "bog " down when I would try to accelerate.
So I got it scanned, and it threw codes P0305 ( cylinder 5 misfire) and code P0420( system efficiency below threshold bank 1) it was recommended that I replace my spark plugs, especially #5, so I purchased all 6 new spark plugs( NGK IX irreduim) changed them all out thinking it would fix my issue... HA, not even close, my SES is still on, still flashes when above 2rpm and still has rough idle. So I then switched my #5 ignition coil with #2 ( bc #2 is so much easier to get to) just in case it's the ignition coil.
What I'm needing advice with, has anyone else has a similar issue? Had the same codes thrown when scanned, and what was the solution to the problem? I'm just really not wanting to spend any extra unnecessary money if possible. I just really need my truck to be running correctly.
Thank you so much in advance for any advice or suggestions!!

[VStar650CL]

The flashing SES means you're getting a constant misfire, the ECM is basically warning you that it may damage the cat (federal regulations). But the P0420 probably means the cat on that bank is already dead or dying, and it sounds like you may have melted it. Is it blowing any oil smoke? If so, get a compression test done on #5, you might have big trouble. Whatever you do, don't keep driving it until you find out the problem. With a dead miss, if it hasn't inhaled the cat yet, it probably will if you push it. If the compression checks okay, go back to basics. Pull the #5 coil, and with a spare spark plug inserted and grounded, see if you have spark. If you do, what did the original plug from #5 look like? Was it a different burn from the other plugs? If the new plug lacks color or is very light or very dark, the injector could be the culprit. Post some plug pics if possible.

[BrittanyTN]

Thanks for your quick reply, unfortunately I didn't take any pics of my spark plugs when replacing them, but my grandfather helped me change them (he's a certified diesel mechanic) and he said that all my spark plugs looked just fine, that none were bad which is why we switched the #5 ignition coil with #2 because he figured changing the plugs weren't going to fix my problem.
After switching the coils I scanned it again and now it's throwing code P0300 (random misfire) and also the original codes P0305 and P0420. And the recommendation was to replace ignition coils, but obviously it's not the coil bc we switched #5 to #2 & it's still throwing a code for #5. So could it be the injector itself, and is there a way to test for it before spending the money on a new injector? It was also said it could possibly be one of my O2 sensors, any way to test for that?
Also, I haven't noticed any oil smoke, and there was no oil anywhere when we were changing out the plugs. I also went ahead and replaced my manifold gaskets just to be safe, while we already had everything taken off today. I'm just at the point of frustration trying to fix this problem. Thank you again!

[VStar650CL]

You're most welcome. Verify that you have spark on #5 first before chasing an injector issue, Nissan injectors rarely fail and are usually the last thing you should look at. On the other hand, issues with embrittlement of coil wiring is not uncommon. If #5 coil does have spark, pull the new #5 plug along with a plug from the other bank and compare the burns, if #5 has a fuel issue it will be either whistle-clean or very dark compared to others. If you don't find other issues, with the P0420, I think there's a good chance your cat is partially melted and restricting the exhaust on that side.

[mdmellott]

A quick test to confirm whether or not the cat has given up the ghost is to use a non-contact digital laser temperature gun. You don't need an expensive, highly accurate one for this test. ~$25 or so from The Home Depot, Lowes, or Amazon is what they cost. If the cat is shot, the temperature right at the exhaust output end of the cat will be less than or about the same as the temperature right at the exhaust input end of the cat. A good cat should measure at least 100 degrees hotter at the output end compared to the input end. Warm the engine up to operating temperature before measuring the temperatures at the ends of the cat. Be sure the laser pointer is landing on the cat pipe and not shining on a heat shield.

[VStar650CL]

A quick test to confirm whether or not the cat has given up the ghost is to use a non-contact digital laser temperature gun. You don't need an expensive, highly accurate one for this test. ~$25 or so from The Home Depot, Lowes, or Amazon is what they cost. If the cat is shot, the temperature right at the exhaust output end of the cat will be less than or about the same as the temperature right at the exhaust input end of the cat. A good cat should measure at least 100 degrees hotter at the output end compared to the input end. Warm the engine up to operating temperature before measuring the temperatures at the ends of the cat. Be sure the laser pointer is landing on the cat pipe and not shining on a heat shield.

Wise tip, Md! Measuring the heat differential between the two cats will also give you a quick idea if one is blocked or occluded.

[BrittanyTN]

Thank yall both so much! We're venturing back under the hood today, and I will be taking the advice yall have given me and putting it to good use!
I'm going to go by my local home depot and buy a laser temp gun before I get to my grandfather's shop, so we can test the CAT. Could a bad O2 sensor be causing the CAT to not function correctly? & if so, is there any way to test for a bad O2 sensor(below or after).
Thank yall again for all the help, it's so appreciated!

[VStar650CL]

Could a bad O2 sensor be causing the CAT to not function correctly? & if so, is there any way to test for a bad O2 sensor(below or after).

No, the HO2S's are there to monitor the cats, they can't hurt it if they malfunction. You'd be seeing different codes if the O2's were an issue.

[mdmellott]

No, the HO2S's are there to monitor the cats, they can't hurt it if they malfunction. You'd be seeing different codes if the O2's were an issue.

I appreciated your comment to me awhile back when you said, "... the front HO2's (or A/F's) are for the ECM, the rear HO2's are for the government."

[VStar650CL]

I appreciated your comment to me awhile back when you said, "... the front HO2's (or A/F's) are for the ECM, the rear HO2's are for the government."

Thank you! Most techs could quote you the same old saw. It's true for the most part, but the O2's are also the "DEW line" for alerting you to incoming cat failure. Super-important on a Miller-cycling engine, as I've noted elsewhere.

[BrittanyTN]

I forgot to mention earlier that I recently pur this vehicle about a month ago, when purchased everything seemed great, no lights on dash, no rough idle, etc. Also, the seller had the gas tank full upon purchase. I didn't start noticing any issues until the gas level fell below half tank this week, and my grandfather mentioned the possibility of bad gas, or old gas in the tank, so we also added some fuel system/cat system cleaner into the tank yesterday while we were working on it.
Is there any possibility of this actually being the cause of my issues? I know it's a far leap( & a bit of hopefulness lol).
We're currently under the hood now looking further into my issues. Fingers crossed we can come up with a diagnosis/ solution. Thanks again yall!

[VStar650CL]

I didn't start noticing any issues until the gas level fell below half tank this week, and my grandfather mentioned the possibility of bad gas, or old gas in the tank, so we also added some fuel system/cat system cleaner into the tank yesterday while we were working on it.
Is there any possibility of this actually being the cause of my issues?

If there was resin in the tank, yes. You could be slowly clotting the injectors. Without dropping the tank to look, the best solution is a gallon jug of SeaFoam (yes, a gallon) added to the tank and then drive it till almost empty.

[BrittanyTN]

Okay, awesome! I'll be purchasing myself a gallon of seafoam tomorrow and running it through my system. With any luck, maybe it will help my issue, if not, looks like we may be replacing my CAT on bank 1. Was really hoping it wouldn't come to that though thank yall again for all the advice and suggestions!

[VStar650CL]

You're most welcome! Keep us updated!

[BrittanyTN]

I'll definitely keep yall updated, and hopefully be able to give everyone the solution when we've figured it out! I've added some sea foam to my tank today with a full tank, and its possible its just my high hopes playing tricks BUT my rough idle seemed to improve almost immediately after filling up, however my SES light is still on and still flashed when I got over 2rpm, so I stayed under 2rpm and drove my truck straight back home ( I live maybe 2 miles from the gas station) and i haven't driven the truck any further then that just to be safe.
I've already checked into pricing on my bank1 CAT thankfully I won't need to pay for labor as my grandfather and myself will be doing all the work. I'll definitely post/ update as soon as any new information happens. Fingers crossed yall! Thanks again!!

[Buzzman]

I had this exact problem last month on my 2002 Pathy.
Code was for #4 misfire, flashing engine light and rough running/idling. Also threw the CAT code, which is just a red herring really.
Started doing it with no warning. Fortunately I was only about 2 miles from home.
All six coils are the same, so I only bought one new one. Too expensive to swap them all out.
Now, because #4 happens to be the toughest one to replace (it's under the throttle body), I took the coil from #2, moved it to #4, and installed the new coil on #2.
Took it out for a run, and exactly the same thing happened: Rough running, flashing light, and misfire code for #4.
I was conjuring up some bad scenarios at this point, but I took the thing apart again just to check the coil, and my work, and it turned out I hadn't pushed the connector in all the way.
It looked like it was in, but it hadn't "locked". I shoved in the connector until it clicked, and voila....it's been running fine ever since.
All this to say: check your connections.

[VStar650CL]

It looked like it was in, but it hadn't "locked". I shoved in the connector until it clicked, and voila....it's been running fine ever since. All this to say: check your connections.

"No click, no good." First advice I give every rookie.