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This "how to" will try to provide you with all the information you need to successfully replace the spark plugs in your Micra (1992-2003 K11). Changing the spark plugs is a simple enough job but a small amount of preparation beforehand will make it much easier and allow you to anticipate any likely issues before you start the job.
Before we start, a reminder:
Always aim to complete any car maintenance work safely. Understand what the work entails and what the risks are, and make sure you can complete the work safely. If you are unsure about the safety aspect of any work you do, read a workshop manual, consult a reputable online source or ask a competent person (mechanic or someone with good electrical/mechanical knowledge). Remember the Japanese motto "聞くは一時の恥、聞かぬは一生の恥" which can roughly be interpreted as "Nothing is lost for asking. Better to ask the way than go astray".
In case you are not already familiar with them, the use of different size ratchet drives is primarily to control the amount of force applied to each component they are used on. So, a smaller drive (1/4") is more suited for smaller components where you do not want to apply a lot of force on them or need more precision when turning them, whereas a larger drive (3/8") is better for bigger components and/or components that need to be tightened to a greater pressure or the turning moment is bigger. Likewise for a 1/2" drive. You will notice when purchasing a socket set that (generally) the sockets included with the set will be restricted to a certain size range e.g. you won't find anything much bigger than a 14mm socket in a 1/4" drive set, or anything smaller than 17mm in a 1/2" drive set, etc. Also, as ratchet drives are reversible (i.e. work both clockwise and anti-clockwise) understand how the direction indicator works. The easiest way I've found to remember this is "lefty loosey, righty tighty" i.e. hold the ratchet upright in front of you and swing the direction indicator on the back of the ratchet to the left-most position for anti-clockwise (untighten) or the right-most position for clockwise (tighten). Some bolts do tighten/untighten in the opposite direction to standard bolts, but this is usually where the bolts are supporting a rotating disc or circular plate of some kind and the action of rotation would (over time) loosen the bolt if the standard direction of tightening/untightening was used. Note that all ratchets are different and might have a rotating disc that you turn clockwise/anti-clockwise to change the direction rather than a swing pointer. Also avoid using any kind of universal joint adaptor or power tool for this kind of job. It is very important that spark plugs are not cross-threaded when you install them and this can easily happen if your extension/adaptor is not held straight or you have no feel at the end of the tool to tell how loose/tight the fitting is. Cross-threaded joints are usually very difficult to undo and (more importantly) might not provide a good seal at the joint, leading to uneven temperature distribution or uneven pressure, which usually results in damage to the component itself and/or the engine.
For this job you will be working on the car's electrical system. The following recommendations therefore apply:
Now, let's move on...
The coil packs in your car are used to create the high voltage electrical pulse needed to generate a good quality spark inside the combustion chamber of each cylinder. The coil packs receive a signal from the car's electronic ignition system that ensures the spark is generated at the correct stage of the combustion process. The coil packs themselves are housed inside an enclosed rubber "boot" which locates directly on top of each spark plug. There is a coil pack for each cylinder of the engine (so, 4 coil packs in total for the K11) and can be easily disconnected from the electronic ignition leads and replaced as needed.
Each coil pack is secured to the cylinder head/rocker cover by a small bolt. Before starting, you may want to spray a little penetrating oil at the base of the bolt heads to make untightening them easier. Although this bolt can be undone with a screwdriver, to avoid stripping out the head it is recommended to use a 1/4" drive ratchet and 10mm socket. This bolt isn't overly long, so start slowly initially, then after a few turns it should be possible to unscrew the bolt by hand. CAUTION: These bolts are not very robust and after being screwed into the cylinder head for up to 20 years it's quite possible they might shear off while being tightened. Prepare for this in advance by making sure you have replacements to hand or can order them easily online. You can sometimes feel that the bolt is about to shear by feeling less tension through the ratchet when you're tightening it and you would expect to feel more tension at that point. Under these circumstances you can of course end up with the thread broken and stuck in the head :( These can be reverse-drilled out and there are examples on YouTube and other sites of how to do this as well as details of what tools you might need. In the final analysis, these bolts do not have to support a lot of weight and should remain located once the boots have been pushed on to the top of the spark plugs, so the correct torque is less critical and you can get away with a minimal level of tightening.
After the bolt is removed, stow it away safely. Now, remove the plug connector at the back of the coil pack that connects the rubber boot to the electronic ignition by pressing the top part of the clip down to release it. This allows you to remove the boot by pulling it straight up off of the spark plug without flexing or bending the boot; remember, this is an electrical component with wiring and conductive solid parts inside of it, and crushing or flexing the wiring/conductive parts may change its resistance value or otherwise snap individual strands of wire (which again changes the resistance value). Stow the coil pack away safely. It is not per-se necessary to keep them in order but it is generally good practice to keep each component allied to its original cylinder in the event that a problem arises later i.e. when you take the coil pack off of cylinder 1, don't unnecessarily put it back on cylinder 3.
Depending on your workflow, you might want to do a visual check of the rubber boot for condition at this stage. Also, give the boot a spray of compressed air and wipe down with a very lightly dampened clean cloth or wet wipe. The aim is to remove any external dirt, dust, oil or carbon without getting any liquid on the connectors (although you may want to spray a little contact cleaner on them if they look dirty). If the boots are in poor condition, cracked or you suspect the coils are faulty the next step would be to either buy a new set of coil packs or look online to see if there is any easy way to test the coils (such as testing the resistance of the coils with a multimeter). As with many other car components, unless the individual items are very expensive it is usually sensible to replace like-components as a set i.e. buy 4 of the same brand coil packs. This minimises the likelihood of having coil packs with different specifications and states of wear in the same engine. The engine relies on all of its cylinders running in tune, and any imbalance will result in uneven running and the engine will end up rocking on its mounts. On older cars, the likelihood is also that if one like-component fails after X years, the others will probably fail at some time in the near future because they have been exposed to the same level of wear. The exception would be where another part of the system it is connected to has previously failed and is the cause of the current problem i.e. a faulty high tension lead or spark plug for one of the cylinders might have damaged that particular coil pack and the other coil packs haven't been exposed to the same level of damage and are probably fine.
Coming soon, hopefully....
