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Replacing Spark Plugs

I have a 2002 Chevy Trailblazer which just turned 100,000 miles. I’d like to change the plugs and was wondering how difficult it may be! According to AllDate it requires a B Skill Level. I have no idea what that means. Appreciate any help regarding the difficulty in changing out spark plugs.

Thanks in advance.

Have the plugs been changed before? If not, you may be in for a tough battle. I would also suggest that you have a set of ignition wires on hand, because you will most likely break a couple while pulling them off. At this age, they need to be replaced anyway…

At this age, they need to be replaced anyway…

Contrary to popular belief…Spark Plug wires do NOT deteriorate over time (if some proper care is administered). I’ve had wire sets last the life of the vehicle (over 300k miles). To keep wires functioning properly…clean them 2-3 times a year with a damp cloth…and do NOT use something like WD-40.

Have to disagree on the degradation of spark plug wires. Plug wires are degraded by age, ozone, and heat. The biggest single determining factor in how long they last is the temperature. On a 4 cylinder engine where the engine compartment is relatively spacious and cool, and the wires are no where near the exhaust manifold, 15 years is common. On a large V-8 where they are in a tight crevice an inch from the exhaust manifold, 5 years or 50k miles is about all you can expect. On an 8-year-old V6, I would look to see how well they are shielded from heat. If they get very hot, they are probably due.

the key word here is: “if some proper care is administered” that makes all the wires needing replacement in about 99% of the autos i know of. how about you?

I’ve only replaced one wire set in the past 30 years…Several vehicles went well past the 250k mile mark when I sold them and the vehicles were running excellent with no mis-fires.

I’ve removed old sparkplug wires that were working perfectly fine to move them out of the way to do another repair on the engine. And the simple act of removing the wires caused the core in the wires to break. When the wires were reinstalled the engine developed a miss.

This happened on a Camry when I replaced the head gaskets. I told the owner they would also need a set of spark plug wires to finish the repair. Of course they didn’t believe me because there was no indication that there was a problem with the plug wire prior to the repair, and that I must have done something wrong. I offered to install a new set of plug wires. And if that didn’t fix the miss I would pay for them at no cost to the owner. But if it did fix the miss the owner would pay for the wires.

They paid for the wires.


Just did the plugs in my '04 a month or two ago. It’s not particularly hard to do but you might need some patience if you’ve never had to separate a GM electrical connector before :wink:

The setup is Coil Over Plug (COP) so there are no traditional “plug wires” to be worried about.

The toughest part I felt was that the COP extension is very difficult to gauge if you have it on the plug or are missing the plug tower, especially on the back plugs that are under the firewall extension. Contrary to older style plug wires, these towers have a spring loaded contact that compresses when you screw the coils back down. There is no “snap” type positive engagement and often I was unsure if it was seating properly.

Make sure you check the plug gaps for the new plugs. Mine were way off, probably because they are meant to serve more than one application.

Also, getting a socket over the plugs takes some patience for the plugs in the back. I’ve certainly done much more difficult vehicles but this was not the easiest set up either.

I used a length of gas line hose on the new plug towers to fish them down into the well and then spin them in the first few threads. Much harder to cross thread that way and gives you greater reach where you can’t see.

You might as well plan on taking the throttle body off and cleaning it while you’re in there. The TB is known for polluting up the throttle body due to it’s crankcase ventilation design. Simple 4 bolts and an electrical connector or two to remove it. You’ll be surprised how gunked up it is.

There’s a great explanation on how to clean the throttle body over at Trailvoy and if you’ve never been to that site- well worth it. You have to remove all the same stuff for the plug job so it helps to see pics of the various stages.

The plug job and cleaning took me about 45 minutes total the first time. Most of it was spent contemplating a wire chaseway mounted in the front that makes accessing the front plug difficult.

EDIT: I just realized I assumed you had the I6 engine. I have no experience with the V motors…

All plug wires degrade over time and subtle misfires can exist that will not trigger a CEL and the driver will not even notice.

As far as I’m concerned the plugs in the Trailblazer should have been changed about 50k miles back.

The 4.3L V6 engine is the only one listed for your engine (in my reference), in your 2002 Chevy Blazer. Did you know that? If you did, you didn’t tell us.
Your engine has coil on (spark) plugs (cop); so, what Twin Turbo told you about cop applies.
V6 engines, which sit side-wise, have 1/2 of the spark plugs in the side of the engine which is next to the firewall. They can be rather difficult to get to. Yours COULD be easy, or maybe not.
I would advise getting the repair manual; but, would you?

ADDED LATER: You’re right, TwinTurbo. It is an inline 6 cylinder engine in a Trailblazer. My error; but, everything else stands as stated for V6 engine applications.

You can test your plug wires with an ohm meter. an open means replace, check the manual for the correct resistance. If it is out of the correct range, due to crystalization of the lead from heat, replace the leads. Check for cracks in the rubber insulation that can cause intermittent misses, and check the lead ends for propper fit to the plug and to the distributor cap if you car is so equipped. Also check for corrosion on the lead ends, you can clean them with emry cloth if needed. Leads are cheap to replace, so if in doubt, just put in new ones.

It’s easy to confuse the two but there’s a big difference between the Trailblazer and Blazer. The OP lists their truck as the Trailblazer. The TB has had the Atlas I6 engine available since its inception I believe. Looking at Edmunds, they only list the I6 in 2002 but I’d take that with a grain of salt…

In my experience wires degrade over time and with use, but at different rates depending on the car. I’ve changed the wires on my V8 Olds probably 3 times already with $80 lifetime sets, due to a slight miss. On my V6’s though, they seem to last twice as long, but it is simply good maintenance to periodically replace the wires.