Spark plugs -- really need to be changed? - Toyota Nation Forum : Toyota Car and Truck Forums

cwm9 · 09-01-2009, 04:50 PM

I understand why spark plugs need to be changed on a vehicle with a distributor cap.

In a distributor cap system, voltage is held pretty much at a constant, and the spark fires when the rotor gets close enough to the pin that the breakdown voltage falls below the coil voltage.

Carbon deposits act like resistors and can alter the breakdown voltage. A fouled spark plug, or one that has enough wear to alter the gap distance, can cause timing problems.

But on a coil pack driven car, like the Corolla, firing happens by computer and is completely independent of spark gap distance. (Thus the admonition not to adjust the gap distance.) So if this is the case, it seems to me that either the spark plug is firing and igniting the fuel, or it isn't.

If it isn't you'll know because you'll get misfires. If it is, then it seems a total waste to replace the plug.

Is there any reason to replace an functioning plug that I'm missing? Because it seems to me that regular replacement of spark plugs in a coil pack car is just wasting $$$....

fishexpo101 · 09-01-2009, 05:04 PM

Doesn't matter if it is fed by a distributor or coil pack - the sparkplug will eventually show wear on the electrodes. Spark plugs are "wear" items, the materials they use now have superior service lifespans, but eventually, the plug will wear and you will have to change them.

Not sure what you are getting at with plug gap - the gaps are preset by the manufacturer due to the materials used in these long life plugs - as most people don't have the correct tools to properly gap an iridium or multi-pronged plugs. Depending on the application - you may have to change the plug gap.

Fouling is another matter altogether - usually an indication of something not running optimally - doesn't matter if it is coil on plug or distributor ignition.

True, coil on plugs give you the optimum control over the spark event, but does nothing to prevent electrode wear. That is a mechanical issue that will happen regardless of the device used to feed the plug.

The ///Man · 09-01-2009, 05:35 PM

I could see not changing the plugs if you are adjusting the gap, but if you just keep runing it without any changes, eventually you will get to a point where the engine runs like crap.

Danimal7 · 10-20-2009, 12:25 PM

What type of plugs has everyone had a good experience with?

I'm looking to switch to NGKs, but I can't justify spending $8/plug on their super dooper platinum plugs. I have heard from a friend who drives an AWD Talon TSi that he used the expensive NGKs and when he switched to cheaper NGKs he was more impressed with just the regular NGKs. From that he said that every car may be different, so I want to know which plugs have Corolla drivers been happy with?

***PhatRoyale*** · 10-20-2009, 02:40 PM

Denso or NGK Iridiums.

Copper plugs are dirt cheap, but you will have to change them out more often.

MadaGnik · 10-20-2009, 04:29 PM

My car was running like crap then i changed my plugs. I used NGK's from autozone they were like $3/plug. My car runs way cleaner now.

Danimal7 · 10-20-2009, 08:15 PM

Thanks!

msrdude · 10-21-2009, 10:28 AM

Spark plugs need to be changed. They wear every time you start the car/drive. I think they spark every time when the engine is on. If you check Toyota maintenance schedule it says to replace every 60,000 miles. I think other makes maintenance schedule has the same thing.

futureneck · 10-21-2009, 01:18 PM

i put some Autolite double platinums in mine and paid about 2 bucks apiece for them. i will just change them when they need it. they irridiums that i put in there before only lasted about 40000 miles anyway and they were really expensive.

futureneck · 10-21-2009, 01:19 PM

Also the factory spark plugs say they last 100,000 in the manual

The ///Man · 10-21-2009, 02:06 PM

Quote:

Originally Posted by futureneck

Also the factory spark plugs say they last 100,000 in the manual

This is ,y look on things. I changed out the originals shortly after I got the car and started daily driving, about 96k. The car ran like complete crap. So while yes you can run them out very far, sparkplugs are a direct look in to how your engine is running and potential problems that might be happening internally. I prefer to run NGK copper plugs and change them out every few oil changes. It only takes a couple minutes and it lets me make sure that all 4 cylinders match.

Crowbar911 · 10-21-2009, 03:35 PM

I changed my oem ones at 30K just so I could learn how.

then I jsut replaced them again at 80K, because I needed to show my girlfriend how to change em.

I didnt think I would feel a difference with new plugs vs 50K plugs, but It made the car runa bit smoother.

Ive been putting in NGK iridiums.