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I am looking into how to change out my spark plugs on my 4 cylinder 2005 Mazda 3.

All I know to do is:
1: Open each cylinder.
2: Use a spark plug socket (with the rubber insert) to remove the old spark plug in each cylinder.
3: Insert new spark plug in each cylinder and tighten it (don't over-torque).
4: Close the cylinder back up.

Given the fact that I am not that experienced in working on cars, I feel like this is too simple. Is there anything I'm missing? Safety precautions? Anything that I need to put on the spark plugs before putting the new ones in?

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3.1 Insert new spark plug and catch the thread manually before using a socket wrench, otherwise you risk to overturn the thread. –  Krom Stern Dec 17 '12 at 5:41

5 Answers 5

up vote 7 down vote accepted

They really are that simple - as long as you torque them correctly, there isn't a lot that can go wrong. They are designed to be as straightforward as possible - they don't require calibration, measurement etc.

Make sure the connector is securely on the top of the spark plug, and make sure you don't get oil or grease on the contacts. And do them one at a time to make sure you connect the correct cable back up to the correct plug.

You may even want to quickly test the engine running after you have changed each spark plug - this way, if you haven't tightened one up properly, you will be able to hear it straight away.

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Prior to removing the sparkplug wires rotate the insulated boot back and forth about 1/2 a turn. This will lessen the chance of damaging the wire during removal. –  mikes Nov 17 '12 at 20:52
    
I switched them out last night, and turned the engine on after each one. Then after completing, I drove about 20 miles to make sure everything worked. Out of curiosity, what sound would hear if something was not done right? –  tarheel Nov 18 '12 at 17:07
    
If your car sounds like a weedwhacker engine instead of a car engine, that's kind of what it sounds like when a smaller engine isn't firing on all cylinders. Larger engines it can be hard to tell. –  Brian Knoblauch Nov 19 '12 at 14:55

Also found this for adjusting the gap for spark plugs:

  1. Clean the spark plugs thoroughly, and don't forget the gauge feeler.
  2. To find the right gauge, look for a spec sheet for your automobile in the owner's manual. Insert the feeler gauge between the electrodes.
  3. If it's to narrow, you won't get it in. Try to bend the electrodes a little.
  4. When the feeler gauge is between the electrodes, hit the top electrode gently or push it against a hard surface.
  5. Try to pull out and insert the gauge again..It should touch to electrodes, but not give any resistance.
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According to my local Advance Auto Parts staff, because of the brand of spark plug that I bought (Autolite XP) I did not need to set the gap. But I have found multiple sites talking about this as well, definitely a good reference for someone that might read this later on. The online owners manual (mazda.ca/MciWeb/pdf/manuals/2005/2005_Mazda3_EN.pdf) shows the gap should be 1.25 - 1.35 mm. –  tarheel Nov 18 '12 at 17:30
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@PerT Could you provide a summary of the content you linked to? Link only questions are are generally frowned upon. Also, adding a brief statement such as "Make sure to adjust the gap on the plugs if they're not correctly preset for your application" would make this a much better answer. –  Mark Johnson Dec 16 '12 at 22:33
    
@MarkJohnson, I went ahead and added the quote from the link. –  Bob Cross Dec 17 '12 at 1:43

I like to put a little anti-seize on the threads before putting the new plugs in. That helps ensure the plugs come out nice and easy the next time you have to do it. It doesn't need very much and make sure not to get any of it on the electrodes.

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In addition to the anti-seize, it's also wise to put dielectric grease on the contacts on the plug wire to prevent the wires from rusting to/seizing on the plugs. –  Brian Knoblauch Dec 3 '12 at 14:18

Generally it's simple, unless you have a Ford Windstar 3.8L engine 1996 model, like I do. Unless you have very long arms and small hands, you can't reach anything from underneath the vehicle, nor can you reach over the top of the engine as a cowling prevents access.

  1. To do the plugs, you have to take out the cowl over the engine to be able to reach everything. That took me 30 minutes to get the upper and lower parts off.
  2. Then you may need a special cable puller if the spark plug wires are hard to get off. One I had broke as I was pulling it off.
  3. Then I had to use a special 3 point flex head rachet wrench to fit in-between cables/hoses and get each spark plug out.

I mention this as you don't want to assume all cars are easy for this and if you have a windstar this should help!

It was the toughest spark plug replacement I'd ever done. To finish I made sure I had anti-seize on the spark plug threads and the boot grease on the spark plug boots.

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I like to use compressed air to remove dirt from around the spark plugs before removing them. Especially if the plugs are on top of the engine and point strait down. Important - aways wear saftey glasses or goggles when working with compressed air (or working on any part of a car)

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