p51mstg

I went to the University of Hard Knocks for my Spark Plug Major, with Minors in Broken Parts and Scratched Shiny Things. Besides doing one at a time, I'd like to add another valuable lesson from my days at the "University": Don't crack the porcelain, a lesson that works equally well for both toilets and spark plugs.

Boring anecdote follows: My first job out of college (real college, not the aforementioned university) was as a traveling finance rep. My job was to drive places my boss never heard of, count inventory at appliance stores and collect money. Not much to do after the stores all closed, other than watch cable TV in motel rooms and find interesting places to eat.

One of the activities that used to keep me busy was doing general maintenance on my company cars. I could've had any car dealer, tire dealer or whatever do it for me, but this was something I could do in any motel parking lotduring commercials on theDiscovery Channel.

These were early electronic fuel injected cars from GM - Celebrity, Corsica, Beretta, Grand Am, 6000 - cheaper was better, as far as the home office was concerned. I'd generally stop at an auto parts store about the time I needed to have plugs changed and put a set of new plugs on the old expense report. Then, at my earliest convenience I'd pop the hood.

Driving anywhere between 200 and 700 miles every day, there were bound to be problems if I made a mistake, and I did that once in a while. If I wasn't careful about tightening the new plugs, I'd crack one and not know it. The next morning, I'd take my suitcase out to the car, start it up, and that's when my haste would become painfully obvious.

Luckily, those cars always kept going, and I'd manage to be a hundred or two miles down the road by the time I found the next auto parts store. Stop in the parking lot of the store, buy new plugs, swap out old plugs right there, and if I was lucky I could get it done without cracking another plug.

After a couple of those incidents, I learned how to keep the socket straight on the plug shaft while tightening.

p51mstg

Sorry, but I feel the need to share one more anecdote from my time at the University of Hard Knocks:

I've changed spark plugs in snowmobile engines for going on 30 years, besides auto engines. I've never used any kind of grease, locktite, anti-seize or whatever. I've never needed it. But, I did learn the importance of making sure the new plugs were tight.

Several of my snowmobiling acquaintences have relayed to me the sound an engine makes when it spits out a plug. There's a loud bang, followed by the sound of the engine running on one less cylinder (on some snowmobiles, that might be silence, because in those days many of them had single-cylinder engines).

I don't know that I've ever heard of the plug being sent through the hood, but would assume it's possible. It takes quite a while for the engine vibrations to shake a plug loose - a hand-tightened plug may go a hundred hours (maybe many hundreds) before it works itself against the boot enough turns to be ejected. Therefore, it's not a mistake with immediate consequences, and may even be caught by someone else before "the big bang".

It's one of those things that needs to be done every time, even though nothing might happen.

I know I'll be flamed for saying this, but with today's computerized engine controls, I don't even see the need to gap the plugs. As longs as they don't look bent, I throw 'em in with no adjustment to the gap. If I was concerned with getting all of the performance I possibly could out of a modern auto engine, I'd still gap the plugs (and, definitely gap all non-computerized engines).

In addressing the OP, I think their best option is to buy a repair manual, like I mentioned in an earlier post, and follow the instructions.

As for not messing with it unless you know what you're doing... well, that's how we graduates from the great UHK (University of Hard Knocks) get a degree! [X(] Basic maintenance is a good introduction to what's under the hood, and there's nothing wrong with that. It also teaches the novice what NOT to do, before they ruin something.

Torch_Vert

A couple comments here:

First, the heads in our Mustangs are aluminum, and the plug threads are steel. These two dissimilar metals can interact and weld themselves together over time. This generally results in stripping the threads out of the head. A dab of antiseize on the plug threads is VERY cheap insurance.

Also, the aluminum threads in the Mustang heads can be stripped out by over tightening the plugs. For most people "tight" means when you have to struggle to turn the wrench. The torque spec on the 4.0L heads is much lower than that point. Ideally plugs should be installed with a torque wrench. Failing that, a bit of caution is in order not to overtighten them.

Second, as far as just throwing the plugs in ungapped, you can get away with this in many cases, as many brands of plugs now come preset to the most common gap for that plug. If your car doesn't happen to use that gap, or the gap got changed during shipping, you could end up with rough idling, misfires or other issues. Again, cheap insurance and checking/adjusting the gaps on a set of plugs takes less than five minutes. If you're going to do a job yourself, might as well do it right.

finch00

this might sound silly but why would you change your spark plugs?

Ken Rogers

I'll have to check my manual to find the spark plug change interval, but I imagine it's something like 30,000 miles. I'm still working on my UHK degree, but something I feel important with a spark plug change is preventing contaminants from falling into the cylendars when making the plug change. My last car would have crud covering the spark plug areas, so I would always brush, wipe and vacuum the area spotless. Then I'd loosen the plugs slightly,and vacuum some more to remove trapped dirt around the threads.

I've had car issues that were due to bad spark plug leads, too. When I hit 30,000 I'll probably replace the leads as well. Somebody mentioned this already, but it's a big one... make sure you only do one plug at a time, to avoid mixing up the leads.

Ken