Most miles on original spark plugs ?

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Originally Posted By: artificialist
I have dealt with people who let their plugs go over 150,000 miles. What often happens is that the ignition coil gets destroyed trying to spark across such a huge gap. By the time they have gone that far, many cars have P0420 codes because the excess fuel harmed the cat.


Sorry, this makes no sense to me. The ignition coil isn't "trying" to do anything.
 
Originally Posted By: cchase
Originally Posted By: artificialist
I have dealt with people who let their plugs go over 150,000 miles. What often happens is that the ignition coil gets destroyed trying to spark across such a huge gap. By the time they have gone that far, many cars have P0420 codes because the excess fuel harmed the cat.


Sorry, this makes no sense to me. The ignition coil isn't "trying" to do anything.

It most certainly is "trying", by building voltage...

Here's the deal, reasonably new spark plugs will fire at around 7 to 10KV(thousands of volts), but the coil has the capability to build voltage to approx 25KV... Sooo if the plug hasn't fired by the time voltage reaches peak, it tried and failed... As the plugs wear the voltage required must build higher and higher till eventually it fires or the spark finds a shorter path to ground(same principal as lightning)... This shorter path is usually through the plug boot insulation or back into the coil itself, which will destroy the coil in time... The spark can also burn through the plug/coil wire(as in the 263K mi Chevy), or even through the rotor or distributor cap...

Summing up, the less voltage the coil must build, the longer your iginition components will last...
 
I had a 1987 Mazda B2000, it had 150,000 on original plugs and wires. I tried to change them myself but ended up taking it to a mechanic who finally got them out.
 
Originally Posted By: Buick92
I had a 1987 Mazda B2000, it had 150,000 on original plugs and wires. I tried to change them myself but ended up taking it to a mechanic who finally got them out.


You try a V8?
 
Oppirs,

If those plugs came out of the Cadillac in your signature (89 Deville), they would be replacement plugs rather than originals. Back in 89, AC & Delco were still considered separate GM divisions for labeling purposes, so the original plugs would have only said AC rather than AC-Delco. Nevertheless, they look like they've given great service for the time they've been in there.
 
I went 200K miles on a 99 4.6 Grand Marquis on the original plugs..I have 121K now on my original plugs in my 05 Vic..When [and if I do change the plugs] Motorcraft plugs will be going back in there again.
 
Originally Posted By: TFB1
Originally Posted By: cchase
Originally Posted By: artificialist
I have dealt with people who let their plugs go over 150,000 miles. What often happens is that the ignition coil gets destroyed trying to spark across such a huge gap. By the time they have gone that far, many cars have P0420 codes because the excess fuel harmed the cat.


Sorry, this makes no sense to me. The ignition coil isn't "trying" to do anything.

It most certainly is "trying", by building voltage...

Here's the deal, reasonably new spark plugs will fire at around 7 to 10KV(thousands of volts), but the coil has the capability to build voltage to approx 25KV... Sooo if the plug hasn't fired by the time voltage reaches peak, it tried and failed... As the plugs wear the voltage required must build higher and higher till eventually it fires or the spark finds a shorter path to ground(same principal as lightning)... This shorter path is usually through the plug boot insulation or back into the coil itself, which will destroy the coil in time... The spark can also burn through the plug/coil wire(as in the 263K mi Chevy), or even through the rotor or distributor cap...

Summing up, the less voltage the coil must build, the longer your iginition components will last...


To my knowledge, ignition coils are not "smart". They do not know the gap that is being bridged with spark. I'm glad to learn more but so far this isn't making sense from an electrical standpoint. I can't find any information online about this being the case beyond internet anecdotes by mechanics (or less).
 
Originally Posted By: cchase
Originally Posted By: TFB1
Originally Posted By: cchase
Originally Posted By: artificialist
I have dealt with people who let their plugs go over 150,000 miles. What often happens is that the ignition coil gets destroyed trying to spark across such a huge gap. By the time they have gone that far, many cars have P0420 codes because the excess fuel harmed the cat.


Sorry, this makes no sense to me. The ignition coil isn't "trying" to do anything.

It most certainly is "trying", by building voltage...

Here's the deal, reasonably new spark plugs will fire at around 7 to 10KV(thousands of volts), but the coil has the capability to build voltage to approx 25KV... Sooo if the plug hasn't fired by the time voltage reaches peak, it tried and failed... As the plugs wear the voltage required must build higher and higher till eventually it fires or the spark finds a shorter path to ground(same principal as lightning)... This shorter path is usually through the plug boot insulation or back into the coil itself, which will destroy the coil in time... The spark can also burn through the plug/coil wire(as in the 263K mi Chevy), or even through the rotor or distributor cap...

Summing up, the less voltage the coil must build, the longer your iginition components will last...


To my knowledge, ignition coils are not "smart". They do not know the gap that is being bridged with spark. I'm glad to learn more but so far this isn't making sense from an electrical standpoint. I can't find any information online about this being the case beyond internet anecdotes by mechanics (or less).


It's a fact, Jack.... I was even told this by a Federal Mogul training/tech rep during a seminar.

The greater the plug gap, the greater the juice required to jump the gap. If you go too long, you can damage the coil because it's worked too hard for too long trying to fire the ginormous gap. Basically, the coil is operating outside of it's intended parameters and will die from heat/resistance in it's windings or a fault in it's own insulation.

The remarks about failed catalysts is also correct - they suffer the (cumulative) affects of a worn ignition system in the way of misfires (hydrocarbons) or poor combustion and the resulting increase in hydrocarbons.
 
Originally Posted By: cchase


Sorry, this makes no sense to me. The ignition coil isn't "trying" to do anything.



To my knowledge, ignition coils are not "smart". They do not know the gap that is being bridged with spark. I'm glad to learn more but so far this isn't making sense from an electrical standpoint. I can't find any information online about this being the case beyond internet anecdotes by mechanics (or less). [/quote]

"Smart" is not the correct wording. A new plug gapped @ .035 with nice square electrodes does not take much voltage to fire. A worn plug with .080 gap and rounded electrodes takes much more power to bridge the gap.

Resistance in the plug (gap, electrode condition) and wire(s) are what create resistance in the circut. Resistance makes heat somewhere. That somewhere being the coil.

Overheat a coil and eventully it weakens to the point that it loses it's ability to create a spark that can jump the gap.

Too much resistance at the plug often leaves the spark looking for an easier way out and the wire is often the victim.

So basically a coil that only needs to put out 10k volts to fire a plug will last longer than the same coil putting out 60k to overcome worn out plugs.
 
I follow the OEM schedule on my '04 Suby, it gets plugs every 30K. I use NGK VPower copper core plugs, which has the OEM part number for that car. With my employee discount, parts and labor on plugs is about $55. 55 dollars every 2 years....big deal!
 
Just to throw some numbers out there. A spark plug that requires 10kv to fire with a gap of 0.04" would have to be worn to a gap of 0.08" to require a voltage of 20kv. I've pulled high mileage plugs but on any car with platinum or iridium plugs I've never seen the gap double.

Does the ignition coil continue to charge until there is a spark? It seems like if that were the case, your timing would end up being off before the ignition coil ever croaked.
 
Dad had over 200k on the #1 plug in his Festiva. Could never get it out wasn't going to mess with it. 2 weeks of PB Blaster and a 4 four cheater bar but finally took a impact gun to take it out.
 
My Maxima had the original in for over 140K and when they came out the gap had almost doubled! The car ran the same after the new plugs.

The current ignition technology really does not seem to be bothered too much by excessive gap.
 
Originally Posted By: cchase
Just to throw some numbers out there. A spark plug that requires 10kv to fire with a gap of 0.04" would have to be worn to a gap of 0.08" to require a voltage of 20kv. I've pulled high mileage plugs but on any car with platinum or iridium plugs I've never seen the gap double.

Does the ignition coil continue to charge until there is a spark? It seems like if that were the case, your timing would end up being off before the ignition coil ever croaked.


I sure the gap vs voltage doesn't follow a linear scale, .080 could need 15Kv or 22Kv... Plus as stated the plug tips "round" with age which increases voltage required, the spark will jump from a sharp point at much less voltage...

One thing for sure, in time 20Kv will burn up the boots and/or coils...
 
Originally Posted By: TFB1
Originally Posted By: cchase
Just to throw some numbers out there. A spark plug that requires 10kv to fire with a gap of 0.04" would have to be worn to a gap of 0.08" to require a voltage of 20kv. I've pulled high mileage plugs but on any car with platinum or iridium plugs I've never seen the gap double.

Does the ignition coil continue to charge until there is a spark? It seems like if that were the case, your timing would end up being off before the ignition coil ever croaked.


I sure the gap vs voltage doesn't follow a linear scale, .080 could need 15Kv or 22Kv... Plus as stated the plug tips "round" with age which increases voltage required, the spark will jump from a sharp point at much less voltage...

One thing for sure, in time 20Kv will burn up the boots and/or coils...


I am absolutely, 100% sure that it is a linear relationship. The voltage required to initiate a spark across anything is a function of distance and is a constant for any material.

Wearing out ignition coils from excessive gap sounds like a tale from the 1970's that persists to this day and perpetuated by mechanics who replace ignition coils and notice that the plugs are worn out and conclude that the worn out plugs caused the ignition coils to fail. I've yet to see something outside of anecdotal evidence and that seems to be based on "well, the coil went bad and the plugs were bad, so..."

I'm open minded as long as someone can provide some kind of meaningful data that jumping a larger gap "stresses" the coil. It goes against everything I know about capacitance, spark discharge, and automotive ignition systems.
 
I got 90k out of mine on my truck and they were OK when I changed them.

On aluminum heads like Mercedes they actually say 4 years or 100k whichever comes first. That 4 year part is important if you want them to come out.
 
I was quoted $340 to change the plugs in my wife's 3.3 l sonata. You have to take the upper air plenum off and a bunch of other stuff. Since I was still getting good gas mileage I waited till I had time to do it.

My point is this is not a 15 minute job like some cars. The plugs are NOT easily accessible. I like the fact these iridium plugs give the option for long service intervals.
 
It really was not that bad to change these plugs on the sonata. Took about 1.5 hours going by the book.
 
Last edited:
Originally Posted By: cchase

I am absolutely, 100% sure that it is a linear relationship. The voltage required to initiate a spark across anything is a function of distance and is a constant for any material.


No way, the amount of compression also creates a variable in the amount of voltage needed to jump the gap...

From a chart in the ARRL Hand book, of course these are "free air" measurements of a sharp point not influenced by the amount of compression in the cylinder...


Gap
inches V_peak
0.015 ___1000
0.02 ____1200
0.03 ____ 1500
0.05 ____ 2000
0.07 ____ 3000
0.08 ____ 3500
0.125 ___ 4500
0.15 ____ 6000
0.175 ___ 7000
0.25 ____ 9000
0.35 ___ 11000
0.5 ____ 13000
 
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