How to: Replace Spark Plugs on a Pathfinder / QX4 with the VQ35DE engine (2001 – 2004)
CAR: 2001 Infiniti QX4
6 x Spark Plugs; Preferably the OEM NGK PLFR5A-11
Ratchet (either 3/8″ or 1/2″, whichever one you prefer. I did mine with the smaller 3/8″)
5/8″ Spark Plug socket
Screwdriver (both types)
Anti-seize (I prefer the copper-based ones)
Start by removing the engine cover. There are two 10mm nuts and one 10mm bolt holding the engine cover to the top of the engine.
Lift up on the metal tabs (the second and third green arrows from the left) and remove the air filter and filter holder (I realize that this is not needed but I needed to replace my air filter so I put this step in)
Unclip the two black hoses (the second and third red arrows from the left) running across the top of the airbox.
Remove the MAF sensor plug (circled in red).
Loosen the hose clamps (the first green arrow from the left) and undo the black hose (the first red arrow from the left).
There are two 10mm nuts holding the airbox in place. Remove them.
I saw these two holes on the front of the airbox but there were no bolts in them. I’m not sure if mine got lost or if it came like this but if yours has bolts here, remove them too.
Pull out the airbox and set it aside on top of the engine. You’ll notice that a black hose is still attached to the airbox. I tried removing this but it was on there very tight and I didn’t want to snap it or do any damage to it so I just left it there as I didn’t NEED for it to come to do the work.
Remove the hose clamp that is holding the intake boot to the throttle body.
The intake boot is held with a 10mm bolt. Remove it.
There is a black hose on the back side (firewall side) of the intake boot (circled in red below). Detach it from the boot.
Now the boot should be free and you should be able to wiggle it out. Once out, undo the blue clip and unscrew the two screws to remove the black sensor thing below the throttle body.
Black sensor thing removed.
There are two 10mm bolts securing two wire brackets to the engine. Remove the bolts for easier access to the coil packs.
Unclip the plug from the coil packs and unscrew the 10mm bolt. Do this for all three on the driver side.
Now on to the passenger side…
Remove the four 10mm bolts holding a wire bundle bracket to the engine. Remove them.
Cylinder One’s coil pack looks different from the rest in that the coil pack plug is on top of the coil pack as opposed to being on the side. Other than that, it’s the same deal. Unplug the plugs from the coil packs and remove the 10mm bolts holding them.
For Cylinders Three and Five, I found it easier to remove the plugs and the bolts if I hold up the wire bundle like this.
Now that all the coil packs are free to move, gently pull on the coil packs to remove them from the engine.
All of them out.
Using the 5/8″ spark plug socket and the socket extensions, remove the spark plugs.
All of them out.
Time to put the new spark plugs into the car. There is no need to gap the spark plugs.
Grab the new spark plug and apply some anti-seize on the threads. DO NOT drench them in anti-seize. Just a dash…
Using a torque wrench set to 20 ft-lbs, torque the new spark plugs back into the engine. The service manual gives a torque spec range of 14-22 ft-lbs so I decided to go with 20 ft-lbs.
Rest is just reverse of removal. Put everything back. What? You want more details?
Put the coil packs back in and hook up the coil pack plugs and the 10mm bolts.
Reattach the black sensor thing back on to the engine and attach the blue plug back on to the black sensor thing.
Screw the wire harness bundles back on both sides of the engine.
Replace the intake boot and reattach all the hoses and plugs.
Replace the airbox and reattach the hoses and the MAF sensor plug back on.
I think that’s all the steps….
I wanted to clean the throttle plate and the MAF sensor while I had everything disassembled so I went and did that too.
If you want to do those too, the tools/parts you’ll need are:
T20 Torx bit
Throttle Body Cleaner
To clean the throttle body…
To clean the MAF sensor (be very careful, this part is expensive) remove the two T20 torx.
Spray the MAF thoroughly with the cleaner and let is dry. It will dry relatively quickly as the stuff evaporates quickly.
I find that cleaning the MAF really helps with rough idle problems. It is also necessary to clean the MAF if you’re running aftermarket oiled air filters like K&N, BMC, etc.. because the excess oil can get on the MAF and result in fouled readings, resulting in rough idle, poor gas mileage, etc.
If you have questions or comments, here’s a discussion of this article! DIY: Spark Plugs with Pictures!