Engine shudders after spark plug change

[blueludedude]

Hello,

I am the proud owner of an '08 Altima 3.5 SE Coupe. It's a great vehicle, and I really haven't had any sort of mechanical problems with it up until now. It's got around 109k miles on it.

A little background info for you - I'm an IT guy, not much of a car person. I've done a few oil changes, changed spark plugs on some four-bangers, and I get the basics of how an engine works. But I am nowhere close to being a mechanic, maybe just a once-a-month weekend one.

Here's my situation. At around 105k miles, following the Schedule B maintenance list, I decided to be brave/frugal and try to tackle a spark plug change on my engine, even though the back three plugs are notoriously hard to reach. Before the spark plug change, the engine ran perfectly smooth, like butter. I followed the excellent instructions/photos on importnut.net: http://importnut.net/nissan-altima-spar ... t-4th-gen/. I'm the second owner of my vehicle, but I assume the plugs that I took out were the originals - Denso FXE22HR11's.

I followed the instructions precisely, with the following differences:
* I installed Autolite XP 5684 (Iridum XP) plugs, which multiple retailers confirm are compatible with this engine. I gapped them at .044 before installation.
* I did NOT replace the intake manifold gasket or throttle body gasket
* No anti-seize, as I have read from spark plug manufacturers that using it can lead to over-tightening of the plugs

Also, although the pliers that I used to help wiggle off the vacuum hoses roughed up the ends of them a bit, I did not notice any leaks, so I did not replace any of them.

After completing the job and putting everything back together, the engine started right up, and it seemed to idle pretty smoothly. However, over the next day or two, I noticed some ever-so-slight shuddering that traveled up through the steering wheel and the seat when driving on surface streets (25-50 mph). When I got on the interstate, it was much more noticeable, especially around 70-80 mph. With cruise control on and my foot off of the gas, I could feel the engine kick and shudder a bit. It would then seem better for a few seconds, then repeat again. The shuddering was worst if I disabled cruise control, let the speed drop for a few seconds, then gave it some gas. It wasn't like the whole car was violently shaking, but there was definitely a moderate shudder coming from the engine bay for a couple of seconds. When I leveled off the speed, it wasn't as bad, unless I stayed around 70-75 mph, where I would feel it kicking a bit. What's weird is if I dropped below that, say around 60-65 mph, I didn't really feel any kick anymore.

So, the first thing I did was take the car to the mechanic down the street. I started it up, took the engine cover off, and he put his hand on the upper intake manifold. It was idling pretty smoothly, but he said that he could "definitely feel it misfiring", but he couldn't tell if it was one cylinder or multiple.

I went back home, put the old Denso's back in the front three slots since those are the only ones that are easy to get to, fired it back up, and still had the same symptoms. So I figured it was a problem with one of the three rear spark plugs or with the intake manifold gasket.

My neighbor and I performed open-heart surgery on the car again this past weekend. I used the same model of spark plugs, we DID change the manifold gasket this time (OEM replacement), and we replaced one of the vacuum hoses that we noticed had a slight leak.

I took the car out for a spin on surface streets, and it seemed pretty good. Maybe a slight lack of power, but no shuddering that I could tell. The next day I took it out on the interstate, and I had the EXACT same shuddering symptoms at 70-80 mph. I also started to notice some very slight shuddering at low speeds and at idle. I took the engine cover off, and sure enough, when I put my hand on the manifold, I could feel it shudder a bit every now and then, so it was probably the same misfire that my mechanic spoke of after the first plug change.

So that's where I'm at now. Two PITA spark plug changes within a month. No problems before, same symptoms after each change. I am looking for suggestions on how to proceed from here.

* If I change out the spark plugs again, I'm putting in the exact same plug that I originally took out, either a Denso FXE20HR11 or FXE22HR11 (or possibly NGKs).
* My neighbor suggested that perhaps one of the spark plug boots or wiring has gone bad. I just find it strange that the engine worked perfectly before I pulled the original plugs out, and the boot/wiring is suddenly fouled up. The only explanation for this is if we somehow damaged the wiring the first time, but we were very careful, and we did not yank on any wires or anything.
* My neighbor also guessed that it might have something to do with the fuel filter. But again, why would this symptom suddenly appear after a spark plug change?
* My guess is that the spark plugs themselves are functioning as designed, based on the fact that we got the same results after both jobs. I just question whether these plugs are really compatible with the vehicle.
* We triple checked all of the nuts, bolts, gaskets, and hoses and they are all connected properly.
* We did not use a torque wrench either time, but we did the standard "extra 1/8 to 1/4 turn after hand-tightening" to ensure the plugs were installed snugly.
* I've noticed a slight hissing sound (with the A/C turned off) coming from somewhere around the top-back part of the manifold. I don't know if it was there before I pulled the plugs out the first time. My mechanic said it was a normal sound. I checked all of the hoses for leaks, made sure they were on all the way, and sprayed them with carb cleaner with the engine running; no change in idle. Can anyone confirm that they hear this sound on the same vehicle with the VQ35 engine?

At this point I'm not sure what to do other than to put in some Denso's or NGK's and see if that makes a difference. Has anyone else ever used the Autolite XP 5684's (aka Iridium XP) with success?

Thanks in advance for any helpful feedback. The only thing I ask is that you don't waste any time saying "Autolite sucks!" or "Only use Denso/NGK!" unless you've tried both and you can personally attest to the fact that one is superior to the other in this type of vehicle. If you check out the Ford Mustang message forums, they all swear by Autolites, and lots of them use them at the track. But I realize that may be comparing apples to oranges since we're talking about an Asian car vs. an American car. However, I also know that they're made by Fram, who gets a lot of flak over the quality of their products, plus they're priced lower, so it does make me wonder how good the quality really is.

Thanks again! I love this car, I love the power, the handling, the CVT... please help me get it back to how it was a couple of months ago!

- Kevin

[seldomseen]

At this point you may strongly want to consider taking your car to an experienced mechanic or the dealership to fix the problem correctly. So that you can resume your happy and proud ownership.

[BamaCoupe]

* My neighbor suggested that perhaps one of the spark plug boots or wiring has gone bad. I just find it strange that the engine worked perfectly before I pulled the original plugs out, and the boot/wiring is suddenly fouled up. The only explanation for this is if we somehow damaged the wiring the first time, but we were very careful, and we did not yank on any wires or anything.

Was the exhaust manifold still hot and possibly lay the spark plug wire on it; I haven't did a spark plug job on the Altima yet so I don't know if that's even possible with our cars, but I know that was something I had to watch for on a Camaro I had? Don't know how visible the rear three are, but it's easy to find if one of your wires have a brake in it. At night open your hood with the car cranked and look over the cables good (don't touch) and see if you see any arcing or sparks coming from any of the wires.

[blueludedude]

Hi everyone,

I already posted about this on a previous thread here: engine-shudders-after-spark-plug-change-t593094.html, but I didn't want to bring that one back to life since it's a bit old now.

I'm hoping there is a Nissan tech / master tech out there that will read this and guide me in the right direction.

Here is my history, as concise as possible:

• 2008 Coupe, V6, bought three years ago w/ about 55k miles (CPO, one previous owner)
• Car ran perfectly up until 106k miles (August 2014)
• Performed spark plug change w/ Autolite Iridium XP plugs
• Noticed some vibration in steering wheel and pedals that was not there before, but only at highway speeds (70-80 mph). No check engine lights ever came on.
• Figured maybe I had a bad batch of plugs or did not gap them properly (even though I am overly meticulous about that sort of thing)
• Performed spark plug change again w/ Autolite Iridium XP plugs. Changed intake manifold gasket this time as well.
• Same symptoms were present, so I decided to try one more time with same plugs as originals that I took out the first time
• Performed spark plug change w/ Denso FXE22HR11 Iridium plugs.
• Fyi I left the old coil assemblies in place after changing the plugs each time because they looked fine.
• Vibration still present, but not quite as bad with the Denso plugs. The car still not feel like it did before the original spark plug change, though.
• I assumed vibrations were misfires, so I took the car to a local mechanic and mentioned that. He drove the car around with his scan tool attached and said he couldn't find a problem.
• I took the car to a second mechanic who performed a full diagnostic with a laptop hooked up to the car. No misfires, could not replicate the issue.
• I did my own Idle Relearn, Accelerator Released Relearn, and Throttle Valve Closed Positioning Relearn in Diagnostic mode. Did not seem to help.
• I took the car to the dealership, and they pointed out I had the all too common "passenger side engine mount damaged" issue.
• I replaced the engine mount with the same OEM part. Vibration was dampened slightly, but it did not help a lot.
• Posted a message on CarTalk forums, and some users suggested that perhaps one of the coils in the coil-on-plugs was broken and not transmitting current, which is why no Check Engine Light.
• I checked the three front coils (took them apart completely) and they were fine. I have not checked the back three because I did not want to go through the pain of taking the engine apart again.
• Vibration has gotten worse over time, and now I notice it at all speeds (not just highway speeds).
• Thinking perhaps it was a front suspension issue, I got all tires rotated, balanced, wheels aligned. Same symptoms.
• Took car to dealership again, they said that I could try replacing the front struts. They tightened a few things in the front suspension, but it didn't help.
• Took car to two other mechanics who both said the front struts are fine. Also, local mechanic said that the other engine mounts are OK.
• The dealer also suggested replacing the front axle seals, where they sit against the transmission. My local mechanic put the car up and laughed, said that there was one or two drops of transmission fluid on the axle, that it was nothing to worry about.
• Dealer said that the leaky seals should not have anything to do with the vibration.
• I did have a couple of incidents around this time where I was on a wet road at a stop, I hit the gas moderately, the front wheels didn't gain traction, and I heard a loud *bang* from the front. So I'm guessing that couldn't have been good for the axle/wheels. This was after the vibration had already started, though.
• The last month or two I have noticed some new symptoms. When the car has been sitting all day or overnight, when I first start it up, it rides more roughly. After it has warmed up a bit (20 minutes?), it still vibrates, but it seems a bit smoother.
• Newer symptoms that go away after driving for a while include a low rumble when I slowly give it a bit of gas. The car does not really move that much (it used to just kind of launch itself whenever I tapped the pedal), but after a second or two the rumble stops, and the car picks up speed. It also does the exact same kind of rumble when I'm slowing down, right before I come to a complete stop (and I can tell it's not brakes/rotors). Also, when turning sharply at very slow speed, there is noticeable mild vibration that was not present before.

So, I'm at the point now where I'm thinking it may be the CVT. The dealer said that they "don't like to just replace the transmission without knowing for sure that it's the source of the problem". However, I don't have much faith in their ability to diagnose problems when they recommended that I replace the front struts when two other shops told me that the struts were fine.

The CVT is under warranty for about 5k more miles (I'm just past 115k miles now), so if that's the problem, I obviously want to get that diagnosed immediately.

Here are the next steps that I can take:

• Do one more PITA spark plug change with Densos, and while I'm at it, make sure the back three coils are OK as well. Since the plugs have been in there for about 6k miles now, hopefully they will also show signs of abnormal wear if a problem is present.
• I have never had the dealer check the CVT fluid. I have taken it to third-party shops (e.g. Firestone), and they have always claimed that they checked it and that it was fine. As far as I know, the fluid has never been changed, and again, I'm at 115k miles. So I have an appointment tomorrow to have it changed by the dealer, but I hate to pay for that if it doesn't fix the problem, especially if the CVT ends up being the issue. So I will see if they'll offer to reimburse the fluid change cost if the CVT is the culprit.
• Take it to another dealer for a second opinion.
• Perhaps disconnecting the battery for a while and doing the relearn procedure again would help. I have no idea, but I could try it.

Again, I still have not seen a single Check Engine Light with all of this, so it's very frustrating. And if the CVT is the problem, it's a really big coincidence that it started acting up right after the first spark plug change.

What would you do next if you were in my shoes? Thanks in advance for the feedback.

- Kevin

[Rogue One]

Unless you're posting something completely different from your first thread, the-powers-that-be prefer that you don't create a new thread to discuss the same topic.

[blueludedude]

Okay. I'll keep that in mind next time. Most forums that I have visited tend to frown more upon resurrecting older threads from the dead.

To anyone who is lucky enough to be reading this specific post first, you can skip my original post from last year and just read the one from earlier today. It's completely rewritten from scratch and includes a lot of new information.

RogueOne, if there's any way to remove my post from last year and the couple of replies, that would be fine by me. I would prefer to completely replace it with my post from earlier today.

Thanks.

- Kevin