Topic: Iridium Plugs: Stick with .35 Gap? What do you think?

[chrisfranklin]

I went ahead and ordered 4 of the Autolite Iridium XP Plugs - I had been using copper plugs, but had been having a pronounced flat spot when accelerating from low RPM.  This could be due to a few different things, but I figured that if I was going to end up toiling under the hood to diagnose the problem, I might as well change out the plugs while I am at it.

So "kids,"  :lol1:  here's a mechanic-type dilema for you :

A 4 cylinder YJ owner has an accel coil (supposedly 'hotter'), accel 8mm wires, and now, Autolite's Iridium plugs (factory preset gap at .35).  The Iridium plugs, with there smaller electrode, are supposed to provide 20% less electrical resistance and require 5000 fewer volts to fire.   So here's the question for you: "what gap should I run these Iridium plugs at?"  

a) .35 - factory spec?
b) .42 - 20% greater than factory spec to account for the lower electrical resistance of the plugs
c) greater than .42 to account for the lower plug resistance + the higher performing coil/wires (but, don't think my coil and wires are on par with the FireWire ignition setup)?  

Note:  I had been searching under Iridium plugs and was led to a site for Hondas.  These guys with factory-preset Iridium plugs (NGK, Denso) gap them wider than the factory preset, seemingly because they believe the lower electrical resistance allowed by Iridium plugs enables a wider gap to be used.  Apparently, they seem to feel that this helps, peformance-wise.  Some of them speculate that the factory preset (ie, "owner not supposed to widen the gap on the platinum or iridium plugs") is done in an effort to prevent owners from scraping off the exotic metals - platinum, iridium - thus reducing the lifespan of the plug.  Course, the Honda guys show how to use a narrow tool covered in tape to widen the gap between electrodes and prevent damage when gapping the more exotic plugs.

[chrisfranklin]

These Iridium plugs arrived today, so I installed them this evening.  Decided to go with a .42 gap.  Gap from the factory seemed like it was .30.

The reports of Iridium plugs causing your idle to increase, at least at first, was true in my case.  I did disconnect the battery for 10 minutes, to hopefully let the computer adjust.  However, still went from around 800rpm to 1000rpm at idle for the first few miles.  Engine then seemed to settle back to 800rpm at idle.   However, upon startup after a brief shutdown, engine still seems to idle high at 1000-1200 rpm before settling back to 800rpm.  

Anyway, engine seemed to warm up faster and idle more smoothly (once it settled down to 800rpm). Engine seems like it has more torque when Jeep is climbing hills at high gear and in low RPM.  Also seems to rev faster. Seemed like the flat spot in acceleration that I had when the engine was under load disappeared, but will check this out some more.  

These Iridium plugs seem like the best that I have used so far.  Have used copper, platinum(!), and the usual well-advertised, "trick" plugs. But, these Iridiums seem to be the first to provide a noticeable improvement in my Jeep's drivability vs. standard copper core plugs.

[Jesse-James]

I'll have to try them next time I change pluge, right now I have a stock coil, 8mm wires and NGK standard plugs. Running a .045 gap with no problems.

[Jeffy]

I've heard good things about the Iridiums with many other applications.  The best thing with the gap is to experiment.  Bump the gap up by .005".  The stock gap should be .035" not .35".  So if you're at .042", you might try bumping it up to .045" and then test it.  Then try .050".  If it doesn't like that and misfires when driving back it down by .020-.030" till it stops.  With my PD system, I'm already at .065".  I haven't tried to go wider.  Although I'm using stock autolites.  I'll probably go with the Iridiums next time around.

[chrisfranklin]

The stock gap should be .035" not .35

Yes, but it's a little known fact that my Jeep was a special order that came with an ignition system so powerful that plug gap from the factory had to be set at 10x that of other Jeeps - .35 versus the puny .035 gap.  

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Whoops, right -  .035 to .042.  & .005 increments

[chardrc]

The stock gap should be .035" not .35

Yes, but it's a little known fact that my Jeep was a special order that came with an ignition system so powerful that plug gap from the factory had to be set at 10x that of other Jeeps - .35 versus the puny .035 gap.  

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lol        super jeep.

[chrisfranklin]

After a couple of days, seems like the computer has adjusted and idle has stabilized back to 800rpm.  Set the gap on these Iridium plugs at .042 and this is with a pretty stock iginition setup - some old 8mm wires and a "nothing special" accel coil.  .042 seems to work ok & doesn't feel like it is stretching the ignition system at all.  

So, basically, am thinking it is ok gapping the Iridium plugs over and above the .035 pre-gap, despite the manufacturer's statement of  "buyers, don't adjust the gap on your Iridium plugs."

[chrisfranklin]

So far, these Autolite Iridium plugs have worked well for me.  Mileage seems to have improved by 1-2mpg in the city.  The computer adjusted and the initially high idle has returned to normal.  I'm gapped at .042, 20% over the stock - this is on a relatively stock iginition.  This gap seems to work well, but I haven't experimented with more gap yet.