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How to change sparkplugs (56K warning)

54767 Views 39 Replies 31 Participants Last post by  angdyogi
So, continuing my series of "easy stuff for which there is no write-up" write-ups, we have changing spark plugs.
Some questions did come up about this, and how I glossed over it in the ignition upgrade write-up (, so here it is in glorious color (as always, as applicable to my `94 5.0, so check part numbers and applications for your engine before you buy parts).

Step 1: Get your tools and supplies together.

From the left, we have a small 3/8" breaker bar, which we hope we won't have to use, a 3/8" ratchet (and yes, I know it needs lubed), below that a spark plug gap gauge (the cheap version, because I couldn't find a wire gauge that went big enough), then a universal joint, a 5/8" spark plug socket, 4 wobble extensions, and 3 normal extensions.

Above those we have, again from the left, two different spark plug boot removers. The red one is a pliers-style from Harbor Freight (cheap, $3 on sale, I think), and the other one is a "hook" style from Taylor (bought from Summit, not cheap).

Above that are the cheap copper Motorcraft plugs we're putting in. Those are ASF42C's, if I am reading the part number in the original picture correctly. Each of those boxes has 4 plugs in it, and the box is labeled SP-450.

In case you were wondering just what a "wobble" extension was, here's an example picture. It allows the extension to enter the socket at an off angle, up to about 8 degrees, I think. That may not sound like much, but it can make a huge difference in accessibility. I got my set of 1/4", 3/8", and 1/2" wobble extensions from Harbor Freight for about $12, and they have been very useful.

Here's another look at that "hook" style spark plug boot remover. You'll see how it's used in a moment.

You'll need some dielectric grease and anti-seize compound.

If you're clumsy like me, a fender cover is nice. Just make sure your fender is clean, so you don't grind dirt into your paint while attempting to keep your belt buckle from gouging it. Keep the cover clean, as well.

Use some compressed air to blow any dust or dirt out from around the spark plugs.

How not to be safe while doing it. Wear goggles over your glasses, or a full face shield (see the ignition upgrade thread for an example), not safety glasses in front of them.

What am I doing here, you may ask?

I'm using that Taylor hook-style boot remover. You put the hook down behind the boot, and pull it out that way. The pressure on the "mouth" of the boot opens it up and helps it to release from the plug.

It's still a good idea to twist the boot by hand (or with the red boot pliers) before you pull on it, because twisting helps the boot to break loose from the plug without putting any stress on the wire itself.

Always always always remove the boots by applying whatever force you apply (twisting, pulling, whatever) ONLY to the boot, NOT to the wire. Pulling on the wire will just break the wire.

You don't need these "boot removal" tools, you can do it all by hand, I just like tools. The Taylor is a great idea, poorly executed. I had to epoxy the hook into the handle after it pulled out the first time I tried it.

It is also important to pull straight out along the same axis as the plug. Otherwise you put too much stress on the boot, and you get this:

That's a torn boot. Bleagh. Fortunately, a phone call to Taylor got a replacement in the mail, for free. I was annoyed that it tore in the first place, though.

Now that the boot is off, you can put the spark plug socket on the plug, and the 3/8" ratchet (with 3" straight extension, in this case). This is cylinder 5, at the front of the driver's side, and it's really easy to get to.

You want to be sure that you are straight on the plug, fully seated, and not twisting it off-axis at all. The ceramic will happily break if you apply force in the wrong direction, and that sucks. Don't do that. Slide the socket on fully, and apply force to the wrench handle only in the proper plane to prevent broken plugs.

Don't apply too much force, either. The plug should come out with a reasonable amount. If you are really cranking on it, and it's not moving, STOP. Remove the socket from the plug. Apply some PB'laster around the plug, let it soak while you work on another one, and try it again later. Don't mix up your spark plug wires if you move on, though. That's why you only do one plug at a time, to prevent mixing up the wires and messing up your firing order. Label them somehow if you have more than one disconnected at a time.

If you haven't changed your plugs in a long time (or ever), or if you see rust on them, you may want to pre-soak them for a day or so with penetrating oil (PB'laster, Kroil, something like that) before you start trying to change them. 2 notes on that: Too much oil on the wires may cause misfires, depending on how crappy your wires are. Too much oil on the exhaust manifolds will cause smoke, and way too much oil will cause fire. Try to avoid that second one, use a tube on the sprayer, spray accurately. Fire under the hood is scary, trust me.

Be safe while turning that wrench as well. Falling off the hub (what I'm standing on, on one foot) and crashing down on the top of the fender hurts your belly and/or ribcage. Try to find something more stable to stand on. (I still haven't gotten around to building a step that fits over the tire, but that'd be nice.) (The white step-stool is not a normal resident of my garage, it was only out there (from its normal place in the kitchen) so that my photographer could see over me for some of the shots.)

Now we take the new plug out of the box and gap it. Here it is at the normal gap for my truck, with a stock ignition (.042 inches).

Here it is gapped for the Sixlitre upgraded ignition (.055 inches).

If you open up the gap too far, just rap it on the top of the radiator support (or any other firm smooth surface) to close it up again.

Drop your newly gapped plug into your spark plug socket, and apply a touch of anti-seize to the threads (so that the next time you change them, you don't need the PB'laster).

Screw the new plug into the head BY HAND!!!!! I cannot emphasize this enough. Start it in the hole and screw it in BY HAND until you NEED a wrench to turn it. (If you're having trouble getting it started, make sure you're going in at the right angle (look at other plugs to figure that out), and don't forget the trick of turning the plug backwards (counterclockwise) until it "clicks", then turning it forwards.)

It may be hard to see in this picture, but I'm holding the end of the 3" straight extension between my thumb and fingers and turning it by hand. No wrench involved. Once the spark plug is in (several full turns), and seated, and didn't bind on the way in or get cross-threaded, THEN you can put a wrench on there and tighten it down. You DO NOT WANT to cross-thread a spark plug. That can result in needing to pull the head to fix, if it's bad enough.

These plugs have a conical base that seats down on the head, some have a crush washer. For this type, a torque wrench can be used, specs in Haynes. The crush washers usually spec a certain amount of turning after the crush washer touches the head, like a quarter turn or something. Look it up in your Haynes or Chiltons. Normally I'm really careful about torque values, but for spark plugs, I just go by "feel", and it hasn't bitten me yet. (Now, of course, it will next time I do it.) Over-tightening can be just as bad as cross-threading, as you can rip all the threads out at once. If you're not comfortable doing it by "feel", use a torque wrench for the final tightening.

Once the plug is back in, we'll put the boot back on it. First, though, we need to fill it up with dielectric grease.

Yummm, pretty. That'll seal out any moisture and keep the boot from sticking to the ceramic of the plug.
EDIT: That's way too much dielectric grease. Just put a bit on a small screwdriver and coat the inside of the boot with it.

Line up the boot on the plug, and slide it into place. You'll feel the clip inside the boot "click" or "snap" onto the end of the plug. It may take some wiggling to get it to do so, or even a judicious tightening of the clip (squeeze it gently with a pair of pliers), but if it doesn't snap on, it could fall off later, or pass spark very very poorly to the plug.

And there you are, you've changed one plug. Only 7 to go.

But wait, you say. What about the wobble extensions? Why do we have those? And that u-joint? And all those different lengths?

Well, here's why:

That's the passenger-side bank. It's a little tight. See that black tube, heading towards the back of the engine? That's in kind of a bad spot.

Yeah, it runs right past all the plugs on the passenger bank. Makes it kind of difficult to get in there and get a wrench on the plugs. However, this is what wobble extensions were made for. I put the spark plug socket on the plugs one by one, and then figured out how to get a wobble extension to plug into it, and used that to get a ratchet on there and get the plug out. Going back in, use the spark plug socket by itself to start the plugs, then use the wobble extension and ratchet again to tighten up the plug. When using the wobble extension, though, be VERY careful about how you're applying torque to the plug. It sucks to break a plug.

(With a set of wobble extensions and some common sense, you'll probably actually have more trouble pulling boots on the passenger side than you will changing plugs, sadly enough.)

As it turns out, I was able to change all 8 plugs using only the 3" straight extension and the 3" wobble extension. One of the passenger side plugs (#1, if I remember correctly), I actually used the ratchet handle without any extension at all. You just have to think about where you have room to turn the wrench. Common sense will get you through, though you may want to start on the passenger side, and then do the driver's side as a kind of a reward to yourself.

Again, hope this helps someone.
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EXCELLENT!!! :rockon :rockon :rockon :rockon

Write-ups like this really help out those of us who are less mechanically inclined to do things the 100% correct way!

Well Done! :beer :beer :beer :beer
Excellent writeup..Very detailed..Having the right extensions definitely helps things and so does the plug boot puller, no doubt.. I have that very same step stool, which has pretty much outlived it's usefulness with the bigger tires. Nice job.:thumbup :beer
I love these great explanations for simple jobs. I always find some small detail that I didn't know or forgot about and stopped doing.

Great writeup, very detailed indeed, makes you realize all the simple little steps that get left out, even with something that most of us have been doing all our lives
Nice write-up! I did it the long way and removed the plastic fenderwells for easier access to the plugs, though.
its somewhat easier for me thanks to a 3in body lift but i can tell you honestly that i would have forgotten the anti seize and wobble extentions. nice job on the write up
mmmm.......wobble extentions..........that would make it so much easier! I need to get me some of those. Thanks.

Anti seize....shit i did forget that, but this is on a 5.0 if you want an easy spark plug change....get a 300 and if you want a harder change try a 460 it doesnt let crawl into the engine compartment anymore..

Tyler aka The Deerslayer
One thing that could be added to a very through writeup is this.

when using the 3/8 universal extension, sometimes its just way too loose to keep the spark plug at the correct angle to get it started in the hole. What I do to "hold" the socket in place is to just wrap the universal with some black electric a few times around just the u-joint extension. That will still let it flex through its entire range of movement but it will not fall down or move out of the attitude you want it in to start a plug.

It may sound stupid, but it will help you.....also you may need to be all the way into the job to the point of when you are trying to start a plugs threads in a tough cylinder for you to actually see the usefulness of the tape.
i used this post as a reference to doing my own ignition upgrade/maintenece. It was very informative. For me the universal joints and a 3 inch extension as well asa asolid 5/8 sparkplug socket with working rubber inside. was all i needed. Did the pbblast trick for the stuck ones and the anti/di-electric before putting it all back together. Also went for the accel coil msd cap and accel wires. - see you on the trails.- Joe.
I just had to use this to find correct gapping on stock ignition and how much dielectric grease to use. Got a question though, if I use too much grease will that inhibit the flow of current from the wire to the plug? Thanks for the writeup!
If your spark plug wires have the proper tension in the clip that fits over the plug electrode, it'll scrape off any excess dielectric grease in that contact area. If it doesn't "snap" onto the plug, you might want to tighten it up a bit.
slick, thank you. I just got crap lil' duralast wires and motorcraft plugs. I'll buy better wires when I get the MSD ignition but these will do a lot when they replace the factory wires later today... also they're gapped to .045 instead of .042 and before I tap them down to that size, I'll see how they work. also the wires were almost free cause it was my 6th purchase at autozone, only paid $3 :thumbup
So It's possible to have a misfire because of too much dielectric grease.
Only if your cables are bad, or not pushed down all the way.
I'm only asking because when I did my wires not all of them got that strong click when pushed down. That could explain why the idle didn't smooth out like it should have. FYI I did the ignition upgrade but not the bump yet.
That was a great informitive tech write up the only hint I would like to add is the use of piece of 3/8" fuel line hose cut to a length needed (3" to 6")depending on the access available slips over the end of the spark plug snugly and makes a safe tool to start the plugs back into the threads where when if it gets started crossed thread you know right away, and save alot of cramps between the thumb and index finger when putting the plugs back in. Thanks Again Sewiv for all your time and energy you spend to help us.
great write up keep em coming.
while changing mine I had a helluva time getting the old wires off. they're Bosch and they're still in good shape so I'm gonna hang on to them just in case. maybe keep them in the truck in a toolbox?
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