Join Date: Feb 2018
Location: Fort Worth Texas
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The difference in .002" mentioned above making the difference in car idle is somewhat ridiculous, at least to me. A difference of that little should make no difference at all. Only big changes like .005"+ will provided the OEM gap was chosen the the middle like all of them are. I routinely set gaps for years at up to .005 smaller to make the tuneups last longer, you set small so the gap wear runs up through the ideal number and it then takes longer to get too big to give issue. I did it on every brand car on the planet and never had any issues at all when I worked garage.
As well, the difference in coil saturation time over say .005" in and of itself will be so little (milliseconds) that the timing has no need to change due to it. The plugs never fire in the exact same place anyway, the moving around on the wire electrode of the jump-to point can have the variance .002" if using a extended tip type plug anyway. And multi-point tips that cannot be gapped are never the same (why I hate them), look at a garbage E3 plug, some of the jump-to points are close to .010" in difference and why they are crap.
Bigger gap is a good thing to work toward but you will stress your ignition parts harder. In my view ANY loss of performance means you are also shortening the life of the plugs, the loss is due to the spark getting weak enough, the mapped fuel then overrides it to begin to slowly foul the plugs and them not burning as clean will then die faster. Less spark has the same effect as too much fuel, if the ECM picks up on it it will lean the motor down to possible damage, unburned fuel being perceived as rich by it. That is potential engine problems. I'd NOT be looking at smoothness ONLY and would drop that gap back down a bit.
Retarded timing also means more heat taken by engine parts unnecessarily. Wider plug gap will lead to better idle but then the car doesn't run as well under load when the ECM goes to WFO full rich fuel, which is harder to ignite.
One way to tell if too much spark before parts start failing is to watch the plugs at the uninsulated portion right under any plug booting. Almost all cars show some slight evidence of spark jumping around the outside insulator porcelain there to get to ground rather than going through the gap as intended. Plugs tend to rust there from the humidity trapped under any covers which are commonly not nearly as waterproof as most think. The quick local heating at a cold weather start then condenses water there to rust and the rust carries spark easily. If that amount of shorting there increases to really show up as carbon streaking then you have too much of something. Once a solid short path is established there then a lot of spark will bleed off to go there and car performance drops off in a miss. I have cured innumerable engine missing issues by simply yanking plugs to then clean that area off really well and same plugs go right back in motor to no miss and they last until the next time years off in the future.
FYI, selling plugs forever proves that not all plugs are set for the exact engine and why they should ALWAYS be checked for gap before going in motor. For one, you have no idea of how many of then get dropped on a hard floor to alter the gap. It's far more than you think. For two, the maker gaps them at only ONE gap and that is the most commonly one used out of all the cars that one plug may go into. Meaning if you don't have the popular gap in your motor the plug gap will automatically be WRONG.
Cruising means low load lean and hard to ignite due to particles too far apart, BUT WOT or WFO (where I come) from means hard to ignite too due to the density, more fuel to have to light off and special problems there as well.
Last edited by amc49; 02-09-2018 at 10:18 PM.