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Dec. 28, 2011 1:31 p.m. belteshazzar SuperDork

i bought my wife's 2003 maxima when it had 100k miles on it. the car ran like a dream. i've got plenty of cars with real problems, so i never bothered to tune it up.

almost six years later now, the car has over 160k miles. it still runs great, no missfires, the service engine light has never been on for any reason. i figured i'd just go ahead and change the spark plugs out of principle. what i found in the motor was a set of platinum NGK's, that had been so thoroughly used, the gap was now over .090! are those conceivably the original plugs? what's the most gap anyone has seen before the car started to miss?
Dec. 28, 2011 1:34 p.m. Zomby woof SuperDork

My Wife's Z24 had over 200,000 KM on it when it started to misfire. I swapped out the original plugs, and it went away. Plug gap was over .100"
Dec. 28, 2011 3:40 p.m. donalson SuperDork

didn't bother measuring but pretty sure the platnium plugs on my dads malibu (2k with 3100 v6) where so worn I was supprised the thing ran as well as it did...
Dec. 28, 2011 5:53 p.m. Streetwiseguy Dork

Modern ignition systems really don't care about plug gap. In the old days, coils were weak enough it made a difference, but now you can practically lose all of the ground electrode, and it will still run fine.

Outside the cylinder is where spark plug misfires come from now. Carbon tracking on the insulator is by far the most common cause of an ignition misfire- like over 90% in my experience.

The other 10% is bad coil-on-plug units.
Dec. 28, 2011 6:04 p.m. Toyman01 SuperDork

I pulled a set out of my work van. Two of the plugs had half of the ground burned away. The gap could have been measured with a ruler.
Dec. 28, 2011 6:08 p.m. ShadowSix Reader

In reply to Streetwiseguy:

What is carbon tracking on the insulator?
Dec. 28, 2011 6:42 p.m. egnorant Dork

Had a set on my Escort that I failed to replace when I got the car with 132,000 miles. While still running great and getting 33/50 mpg at 250,000 miles I found the originals that I had bought still on the shelf! It still had the factory plugs in it at 250,000 miles...I was shocked and amazed.

Gap on 2 of them were unmeasurable as the gap gauge went to .100.....then there was a lip that I give another .010 or so and these plugs cleared that gap with ease.

Last plug change at 362,000 miles showed a gap of .070 with .050 being the correct gap.

Bruce

Thge color on all the plugs was great too!
Dec. 29, 2011 7:13 a.m. Streetwiseguy Dork

Coils put out enough power to jump down the length of the insulator, if there is anything stuck to the insulator that is even remotely conductive. Moisture, particularly off a salted road, is probably the most common thing to start it, but dirt and grease from your spark plug socket, or greasy fingerprints will cause it too.