AR51 miss

[dwh4784]

Awhile back I threw a set of these in my car based on numerous recommendations. They are great under power, but cruising around under 2K RPM's I have a constant obnoxious miss that was never present before. I gapped them to the stock specs, should I shorten the gap a bit? Or should I put the regular plugs back in? I'm not running a crazy setup.

[RoadWarrior222]

Yeah, they could have effectively pulled timing, not in degrees but milliseconds, so closing the gap just a tad might improve things, the 2-3K part throttle range in most manufacturers ECUs is meant to have spark retarded to hell for emissions purposes, so just a tad more might have been too much.

Also check your wires for spark burn pinholes.

You could also try jiggling your base timing by half a degree or so, but that depends on how your top end WOT knock tendencies are.

[GLHNSLHT2]

how old are they devin? They're copper racing plugs, they have to be replaced more often than platinum or iridium plugs. Are you sure the plug wires are on secure? Are they all the way seated into the distributor cap?

Usually plug issues will show up under power.

[dwh4784]

They've been in there less than two months, and I noticed the miss immediately after installing them. I made sure they snapped in when installing them, made that mistake before! When I have time I'll pull them out and try closing the gap a bit.

[RoadWarrior222]

BTW I sidegapped champions on a DD and gap erosion on those was chronic, took them out after it became apparent I'd have to regap about every 2 months... yes it would get rough/miss... but could feel the "edge" when they were fresh.

[GLHNSLHT2]

Odd Devin, I've got AR's in the new yorker, the gap is way worn as they've been in for a couple years now but still no random miss. They're in the Jeep and were in the daytona too. We even threw a set in Luke's Van.

[dwh4784]

The car just hates to be messed with. I've never had to put in that spare injector harness after all of the trouble I was having, it just went away once I stopped fiddling with it.

[turbovanman²]

I'd say you have a bad plug, you broke one, bad plug wires/rotor/coil. I've ran them too with no issues.

[wallace]

What heat range would the ar51 be compared to the stock champion plug? RN9YC?

[turbovanman²]

I would guess they are like a BR9ES plug.

[GLHNSLHT2]

They are the same heat range as an RN6YC Champ.

[dwh4784]

Finally got around to pulling the plugs, here is the verdict. #4 has a chunk missing off of the porcelin. No idea how or why that could happen. But I put the old set of plugs back in and it runs smooth as silk again.

[turbovanman²]

2 reasons for that, you either cracked the porcelin if you gapped them and put a side load on the center electrode or detonation.