Did I get bad plugs?

SC Maintenance · Apr 9, 2025

Dave1027 said:
OP,

What type of plugs were in the Xterra when it was working normally?
What type of plugs did you replace them with?
Did you check the gap before installing?

Plugs are NTK DILFR5A 11. They are the OEM plugs - if you pull OEM they are identical. If you go to the dealer they will sell you a NGK boxed plug with the same number that says Nissan and NGK on the box.

There laser iridium - and NGK says do not gap them - you can hurt the tiny electrode. The gaps "look" OK on these two.

Dave1027 · Apr 9, 2025

You must go by the engine manufacturer's gap spec regardless what NGK says. That and you can gap laser iridium plugs without harming them but you must take care not to pry on the tiny electrodes. I recently installed new NGK Ruthenium plugs in my old BMW. The plugs came gapped at .044 but BMW gap spec for that engine is .032. I was able to set the gap at the proper .032 and the new Rutheniums work flawlessly. Even better than the Iridiums they replaced.

kschachn · Apr 9, 2025

SC Maintenance said:
Plugs are NTK DILFR5A 11. They are the OEM plugs - if you pull OEM they are identical. If you go to the dealer they will sell you a NGK boxed plug with the same number that says Nissan and NGK on the box.

There laser iridium - and NGK says do not gap them - you can hurt the tiny electrode. The gaps "look" OK on these two.

View attachment 272648

Yeah I never gap new plugs anymore. In over a combined million miles on my vehicles I've never had an issue with a misfire. I just don't think it matters much with modern tip materials that do not erode as they did years ago.

SC Maintenance · Apr 9, 2025

Dave1027 said:
You must go by the engine manufacturer's gap spec regardless what NGK says. That and you can gap laser iridium plugs without harming them but you must take care not to pry on the tiny electrodes. I recently installed new NGK Ruthenium plugs in my old BMW. The plugs came gapped at .044 but BMW gap spec for that engine is .032. I was able to set the gap at the proper .032 and the new Rutheniums work flawlessly. Even better than the Iridiums they replaced.

I'll check the gap on these two later. There into the trash either way so nothing to hurt.

Dave1027 · Apr 9, 2025

Also, NGK recommended not gapping the Ruthenium plugs for the same reason as the laser Iridium plugs.

zzyzzx · Apr 9, 2025

SC Maintenance said:
So walk me through it.

At 410K miles it could be anything and everything. Meaning do you own a compression tester?

mk378 · Apr 9, 2025

Some oil on the outside is not a big deal unless it is enough to flood the coil.

Does the car's regular user let it sit and idle a lot?

SC Maintenance · Apr 9, 2025

mk378 said:
Some oil on the outside is not a big deal unless it is enough to flood the coil.

Does the car's regular user let it sit and idle a lot?

She does not.

4wheeldog · Apr 9, 2025

If you aren’t using fuel additives, I would consider suggesting that your daughter try a different station for a fuel fillups. Though not the same, the deposits on those plugs remind me of stuff I used to see on aircraft plugs when my airplane partner got lazy about leaning the mixture when at very low throttle settings.

SC Maintenance · Apr 9, 2025

OK, so I measured the fouled plugs gap.

The one mis-firing was somewhere between 0.042 and 0.044. The one that was showing no misfire but still fowled, was 0.044 or maybe a little bit more - 0.045. Here is the factory spec - 0.043. I am pretty sure they are gapped correctly.

This is the exact plug Nissan specs, right from the Nissan manual. They are factory gapped correctly.

So I do not think the gap was my issue.

Also had kid check the oil. Its right where I would expect it to be at this point - down maybe 1/4 quart from when I changed the oil last 3000 miles ago. Its not using any appreciable amount of oil.

No issues since I changed the plugs. I am still leaning to either bad plugs or I am having random coil fails at 400K? I have now changed 3 of 6. plugs / coils. I think I will just fire the parts cannon and change the other 3?

SC Maintenance · Apr 11, 2025

So I made it down to where this car is, but it was starting the rain and the engine was hot. So I decided to just pull the new plug from the cylinder that was missing before. This plug only has 100 miles on it or so, but it looks good to me?

All the fuel trims and other values look good. LTFT doesnt vary much from 0 on either bank. MAF is 3.7 g/s at idle (4.0 Liter engine, idles maybe 600RPM.

So whatever it was I think its fixed? I did bring my borescope but it didn't have an SD card in it

. So picture of a picture. Looking down the plug tube there is some gunk below but maybe that was from before when it was leaking - did the calve covers maybe 20K miles ago. No oil in the tube I can see?

Thought you might like to see the cylinder at 410K miles. Not great, but not bad?