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-spark-plug-replacement-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 not-so-easy 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 stinks!” 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; please help me get it back to how it was a couple of months ago!