P0301 came back, could use some advice please

[outback97]

This is going to be a lot of text and 'splaining, followed by a few questions.

We have a 2006 OR with about 126K miles, spark plugs were changed by a Nissan dealer about 10K miles ago. A couple months ago it ran really rough and threw a check engine light scanned as a P0301 code (cylinder 1 misfire). It doesn't get driven much in the winter, and had been sitting, the battery was older, and so I thought the low power of the battery could be causing the problem. Got a new battery a couple months ago and it seemed like all was well, but now it has started really rough a few more times and I got a pending P0301 on my Scangauge. Most times it starts and runs normally, but when it does this the vehicle shakes pretty aggressively upon cold start, then smooths out and seems to run normally after warming up a bit.

I've never really done anything with spark plugs or coils so this is pretty new to me. I ordered a few Hitachi ignition coils and decided to try to replace coil #1 to see if that fixed it. Seduced by reading reports and watching videos online of more competent mechanics saying you could easily do this without removing the intake plenum, that's what I attempted to do. Took out coil #3 for more access, but that damn #1 coil just fought me every step. I finally got it out, and took the #1 spark plug out as well to check it. It seems like it's OK to me.

Spark plug #1:



I cleaned up the area* as best I could and got ready to install the new parts. Here's where things started to spiral a bit. I tried to install the new ignition coil into #1, and it's just not working for me. I could not for the life of me get everything lined up, and I couldn't get the connecter to snap onto the new coil. I finally gave in and started removing the plenum because I was getting frustrated trying to work around it and contorting my hands under there. At first I was just going to lift up the plenum to give a bit more clearance, but eventually decided the whole thing needed to be out of the way. This made access to all the cylinders easy. I decided to install new ignition coils in at least locations #1 and #3 because it's such a PITA to get to these.

Plenum removed, new Hitachi ignition coils installed in #1 and #3 cylinders.



Next I try to reattach the plug to the connector on the new ignition coils. #3 goes on just fine with a satisfying click and positive engagement. But #1 absolutely refuses to click on. I battled this thing forever and finally noticed something odd.



See the green gasket around the plug? #3 is normal and #1 is really swollen, that's what was preventing the plug and coil from engaging no matter how much I squeezed them together. *I had used some Deoxit D5 spray on the #1 connector, reasoning that maybe the P0301 could have been from a poor connection. I guess the solvent in the contact cleaner just swelled that gasket right up Anyway, continuing my errors, I tried to fish that gasket out of the plug so that it would hopefully dry out and return to normal size. But of course I tore it.



So as it stands right now, I have ordered a plenum gasket set and some connectors like the ones shown above, in the hopes that I can carefully remove the gasket from one of them to replace the torn one on the truck's #1 connector.

Questions:

1) Any better solution to the torn gasket than trying to put a new one in there? I had thought about just stuffing the torn one in and squirting some dielectric grease in to the void, or improvising a gasket with some silicone material.

2) While everything is torn apart, what else should I be doing in this area that I'll regret not doing later?

3) I believe all the ignition coils were original, and I know they're not typically a preventive maintenance part, but I was planning on replacing all three ignition coils on the passenger side while they're easy to get to. Good idea?

4) Once this is all back together, if I still get a P0301 code... what next?

 

[TerryD]

I suggest putting on the new gasket with a dab of dielectric grease on it to help seal and lubricate it.

 

[RamblinRover]

1: As you have already ordered the seals with the new connectors I'd say put them on. You could have gotten away with putting dielectric grease in the connector and calling it a day most likely but might as well give that extra protection and put them in. I would put grease in all the connectors anyways. I would also put it in the boots to make getting them off easier in the future.

2: I would put plugs in if you haven't already. I would also think that the PCV is easier to get to at this point and as it's a trouble area as I understand it for these I would change it. I would check the hose that runs between the valve covers for swelling or leaks, I would also look at the valve covers and make sure they aren't leaking as they are easy at this point if they are.

3: This is up to you. It's not normal maintenance and they can be expensive on some cars. That being said it's easy at this point.

4: You need 3 things for combustion - fuel ( this includes air) , spark and compression. If you replace the plug and coil and still have a misfire you could have a issue with the wiring this is highly unlikely though. Leaving fuel and compression. The fuel portion could include a bad injector and unmetered air ( vacuum leak ) the injector is not as likely and would normally not go away with a temp change. I have seen cars that have vacuum leaks when cold at the mating surface of the lower intake plenum and the head surface. GM's had a big issue with this. Check by spraying around the #1 intake runner when the car is cold and look for a smoothing out of the idle or a change in engine speed. There are other possible causes but I'm guessing the coil and plug will take care of the issue. If not we can go from there.

 

[outback97]

Thanks guys. Parts are starting to arrive, so unless I have a problem with porch pirates this afternoon, I should have them in hand tonight.

Still on the fence about spark plugs. I did order a set, but since the existing ones only have <10K miles on them... I don't know. We only drive this thing a few thousand miles a year. Our '09 is at around 110K miles on the original plugs, so if I don't use them in the '06 I can put them in the '09.

I decided to order both cam position sensors since they should be a little easier to get at while this is torn apart. They're original as far as I know, and although we haven't had any codes indicating problems, I figured it'd be good to do as preventative maintenance. I'll keep the old ones as trail spares.

The PCV valve is probably original as well. I'm thinking I'll pick up the PCV valve 11810-EA200 and hose11823-EA20A and do those while I'm in there too.

I appreciate the responses.

 

[TerryD]

Swap sides with your current plugs. Firstly, the Driver's bank is MUCH easier to access. Second, if the issue is a plug, it will move to the easier to access bank.

In my experience, coil issues usually are complete failures or they show up when the engine is hot.

You might check your insulators (boots between coil and plug). They can get old and leaky and allow spark to ground to the tubes instead of jumping the gap on the plug.

While you have the intake off, you might also look at your valve cover gaskets and tube seals to see if you need to replace those. They get old and brittle and begin leaking. You have to replace the whole valve cover on the VQ40 even though there are listings for spark plug tube seals. The listings are incorrect.

 

[outback97]

Swap sides with your current plugs. Firstly, the Driver's bank is MUCH easier to access. Second, if the issue is a plug, it will move to the easier to access bank.

In my experience, coil issues usually are complete failures or they show up when the engine is hot.

You might check your insulators (boots between coil and plug). They can get old and leaky and allow spark to ground to the tubes instead of jumping the gap on the plug.

While you have the intake off, you might also look at your valve cover gaskets and tube seals to see if you need to replace those. They get old and brittle and begin leaking. You have to replace the whole valve cover on the VQ40 even though there are listings for spark plug tube seals. The listings are incorrect.

Thanks Terry.

I can see the benefit of swapping sides to narrow down the problem. But if I’m removing all the plugs anyway I might just replace them all.

So far the boots seem ok and valve cover gaskets aren’t leaking.

I did notice a small leak at the back of the passenger side, I think it’s coming from the cam position sensor. I’ll be replacing that too so hopefully that helps.

Also I was able to hack one of the new plugs apart and got my $13 replacement gasket.

 

[TerryD]

Thanks Terry.

I can see the benefit of swapping sides to narrow down the problem. But if I’m removing all the plugs anyway I might just replace them all.

So far the boots seem ok and valve cover gaskets aren’t leaking.

I did notice a small leak at the back of the passenger side, I think it’s coming from the cam position sensor. I’ll be replacing that too so hopefully that helps.
View attachment 22537
Also I was able to hack one of the new plugs apart and got my $13 replacement gasket.
View attachment 22538

IMO, until you narrow it down to a plug, don't change them. While the risk is small, it's not zero, that you could install a bad plug and just confuse the issue.

Stick to the plugs you have and move them to easier to access locations until you are SURE it's the plug.

This is an imperative part of troubleshooting that gets folks in trouble and they spend a bunch of unnecessary money or lose interest in their vehicle.

 

[outback97]

IMO, until you narrow it down to a plug, don't change them. While the risk is small, it's not zero, that you could install a bad plug and just confuse the issue.

Stick to the plugs you have and move them to easier to access locations until you are SURE it's the plug.

This is an imperative part of troubleshooting that gets folks in trouble and they spend a bunch of unnecessary money or lose interest in their vehicle.

That totally makes sense from a diagnosis / troubleshooting perspective. I feel by the time this is put back together I will have introduced so many other potential variables though.

I am disconnecting and reconnecting numerous plugs, putting in some new ignition coils, some new hoses, new cam position sensors, uninstalling and reinstalling spark plugs (or new ones). If it's misfiring occasionally because one of the last set of plugs is worn, and I swap plugs from one bank to the other, then the similar aged / mileage plug that was on the other side goes out soon, I'll have to take everything back apart and I'll wish I had just put new plugs in...

But you're probably right about the proper troubleshooting path. I'm trying to not get too wrapped around the axle on this job, which has definitely grown in scope.

I don't know how I didn't see this before, but there's a great how to writeup for spark plugs and intake gaskets here:

How-to: DIY Spark Plug and Intake Plenum Gasket Replacement

With a lot of forum posts dropping like flies due to Photobucket’s new policies, a new How-to needed to be posted for changing out spark plugs on your newer model Xterra, Frontier, or Pathfinder. Preliminary acknowledgements go to rouguebuck on TNX who had the most complete write-up I found...

www.xterranation.org

 

[jsexton]

you are running super lean on cylinder 1. I'd replace the fuel injector.

 

[outback97]

you are running super lean on cylinder 1. I'd replace the fuel injector.

Hmmm. How can you tell? From the spark plug condition?

I will have to research that… might be above my comfort level as a DIY job considering this project is the furthest I’ve been into the engine bay.

Current status is I’ve replaced both cam position sensors, PCV valve and a couple hoses, spark plugs and 1 and 3 ignition coils.

Was all ready to replace plenum and hook everything back up tomorrow night. Maybe not just yet.

Thankfully we have two Xterras since we are going camping this weekend. Must get out of the city!

 

[jsexton]

Hmmm. How can you tell? From the spark plug condition?

I will have to research that… might be above my comfort level as a DIY job considering this project is the furthest I’ve been into the engine bay.

Current status is I’ve replaced both cam position sensors, PCV valve and a couple hoses, spark plugs and 1 and 3 ignition coils.

Was all ready to replace plenum and hook everything back up tomorrow night. Maybe not just yet.

Thankfully we have two Xterras since we are going camping this weekend. Must get out of the city!

Yea. Google lean spark plug and you will see what I mean right away. I’d say you definitely have something fuel related going on with that cylinder. Injector seems like the most obvious/likely issue.

 

[outback97]

This is overdue for an update. We got out for some very much needed dirt therapy with the other Xterra:



I did look online for examples of lean spark plugs, and to be honest I am not seeing what is probably obvious to someone that knows what they're looking for. I did see that the passenger side bank was a bit drier looking and the driver's side was a bit wetter, but showing them in person to a couple guys I work with that have some mechanical experience, they didn't notice anything that concerned them.

These are the plugs and they're oriented as they would be looking straight down at the engine from above

2 1
4 3
6 5



I couldn't find any good walkthroughs about the injector removal / replacement, so I decided to table that for now and just get it back together and running to see how it does.

I installed the following new parts: all six plugs, ignition coils on #1 and #3, PCV valve, two hoses, both cam position sensors, and the plenum gaskets. Putting things back together was definitely easier than taking apart for the first time. If I end up having to do anything with the injectors later, I'm sure the disassembly will go a lot easier now that I know how to do it and have figured out what works and doesn't.

Once all was back together, it started up and ran well. No CEL. High idle. I did the relearn for the throttle body and got the idle back to around 700 RPM where it is supposed to be.

I drove it a bit and it seems to be running great. My wife has now driven it a handful of times and reports that it's much better than it was before... so fingers crossed that all is well.