Hey forum!

I just finished a 200k tune-up on my '07 maxima. Replaced all sorts of stuff including spark plugs, valve cover gaskets, alternator, ac compressor, and the radiator.
Definitely not an easy feat!

Anyways, I replaced all of the spark plugs with NGK 5018 (Platinum Plugs) when I was in there. Yes, I know I cheaped out rather than going with iridium. I also didn't know that the spark plug boots were replaceable until after the job was completed.

Are these cars temperamental when it comes to spark plug type?

Started the car up and it would not idle correctly. Figured the idle relearn needed to be completed since I took of the throttle body. Nope, misfire on cylinder 5.
I ended up swapping the coils, and the misfire followed. Figured the coil fell off the toolbox at some point. Replaced the coil and boot to fix the misfire. Took the car on a one hour spirited drive to celebrate.

Thank god I didn't have to remove the intake again! So I thought....
Flash forward a week later (this week):
I was driving the car to back and forth to work with no issues and ice cold ac! Until, I had to limp it home because of a cylinder 3 misfire.
The car ran just fine before I did all of this work, and now I am getting misfires like crazy.

The car will run fine one day, then I have to limp it home the next. What gives?

I have another good coil on hand that I am going to swap in this weekend, might replace all of the boots while I'm in there. Just wanted to gather opinions before removing the intake again.

TLDR: Intermittent misfires on two different cylinders after spark plug replacement.

 

Well it took me a few hours, but the misfire is fixed!

I put the known good coils on the back side of motor, and swapped the rear ones to the front.

The misfire followed the coil from cyl 3 to cyl 2 (which only took 2 mins to swap out with a good one).

I measured the coil resistances to score good ones at the junk yard. Might post the numbers here later!

Must be coincidence that two coils went bad after changing the spark plugs? Maybe the new spark plugs have a higher resistance?

 

I notice the boots degrade over time and start arcing. Pretty sure you will get more misfires in the future as the OEM coils are getting pretty old by now. Most likely you started experiencing the misfires more because the boots are failing and disturbing them when you replaced the plugs and caused a bit of a crack to appear allowing leakage. After this happened to me in my 7th gen I went ahead and replaced all the coils the last time I replaced the plugs at around the 350-400,000 mile mark as I too started with the random misfire. So, knowing that was going to be my last "plug change" and I really hate that plenum...Didn't want a cascading failure down the road.

 

...if youre at 200k, I'm pretty the jacketing on the wires themselves, running inside the harnesses, is starting to deteriorate...usually by the connectors, and definitely anywhere , those little standoff thingies, that hold the harness off of the block... if the tape that holds the wires bundled, crumbles to dust upon touch, I'd give it a thorough looksy.....the two connectors on the left hand rear of the intake plenum are susceptible too..... There's just no space for the heat to go anywhere...
if cyl.#5 went first, now cyl.#3....hmmm, I wonder why?
Because they were all installed at the same time....so it's safe to say, you should change the 5 remaining, so u don't curse urself when cyl#1 goes next

 

Here is the thing ....You downgraded your OEM plugs by going with the NGK 5018 (LFR5AGP) Platinum Plugs, as far as the quality and quantity of the materials used .
The OEM NGK 6240 ( PLFR5A-11) Laser Platinum plug is a higher quality, longer lasting plug that utilizes a lot more Platinum (Double Actually) in it's manufacturing per plug (hence the price difference) , with both the electrode tip and the ground electrode tip both being Platinum and the electrode tip being near double the size of the NGK5018 the longevity of each can not be compared.

The main issue with your purchase of the NGK 5018 plugs is that they are not gapped properly (0.39 to 0.40) out of the box for a 2007 Nissan Maxima, they are gapped nearly 10% narrower then the NGK 6240 which come properly gapped out of the box at (0.43 to 0.44). You not mentioning properly gapping the NGK 5018 plugs leads me to believe you didn't. That 10% makes a huge difference in idle quality and performance on the 3.5 VQ....pair that with assuming you are using the proper higher octane gas and how, where and when it ignites in the cylinder, the spark plug gap is incredibly important. The coils at 200K should all be replaced with OEM or High Quality coils.
With the Maxima being such a pain in the *** to work on the firewall side of the engine for plugs and coils etc, spending now and doing it right with high quality parts is must to avoid so much aggravation with the ignition system. Go and properly gap those plugs.

 

that's some of the best advice I've gotten here...you know your ****, man! thank you