After putting in the LT4 motor 60k miles ago, I pulled the plugs after 20k and they looked fine, they were AC Delco platniums 41-943. I cleaned them off checked the gap which was at .050 and reinstalled. Lately it been idling a little rough and misfiring ever once in a while....40k miles since I cleaned them, 60k miles total.
Here's what they looked like...with the scanner hooked up the BLMs were still good, 124-134 so I don't think it could be from running extremely rich or lean..although it just barely passed emissions with 143 out of 143 HCs allowed last week. It was all 8 off them, but the 8th one fell behind the grill and I couldn't fish it out all 8 are similar.

What does this look like...or do platniums just not last that long? Can't really remember what they looked like before when I had them out, that was 3 yeasr ago, I read about the "puck" falling off Delco platniums, but it looks like everything is there and the same as they were before when I had them out. Gap was still .050 on all of them too so I don't think anything got burned off. Replaced with NGK TR55IX and now the BLMs are 128-132 and idles perfect.

 

http://www.gnttype.org/techarea/engine/plugs.html

One of them you got there is really ashy. Pull a compression reading from the cylinder that came out of vs. the rest. Worn rings??

 

Looks like the seals did not set right or your o2s are trash check both, first i would check the o2 to see what reading you are getting.

 

Looks to be running lean, Check out the o2's as stated above. Thats the best place to start.

 

Go here and look at the explanation for "ash fouled".

http://www.gnttype.org/techarea/engine/plugs.html

Either you had an additive in the fuel or you are burning oil.

 

I mentioned the O2s / BLMs were still good, 124-134 and after changing to new plugs went to 128-132 across the board.
I also double checked them with my wideband and they seem to be right around 14.1 at cruise, a little richer at 13-14 during acelleration and 13.1 at WOT.
This motor has consumed oil since it was installed, about 1 qt every 1500 miles or so. The motor had 66k miles when I got it, when the heads were off I looked at the cylinders and the cross hatch marks were still in them, looked like it had never been ran much. The shop the did the build said LT4 motors had rings that were not as stiff as LT1s ...they didn't exert as much pressure on the cylinder walls and that oil consumption was common on LT4s so we didn't bother with having it re-ringed since there was no signs of wear on the cyl walls.

I'll do a compression check this w/e on it, should have done it when I changed the plugs but didn't have time.

 

You said you had previously cleaned the plugs - how did you clean them? Why did you clean them? Were they fouled?

 

I just removed them to see how they were fairing in the newly installed engine..they were fairly clean, no ash build up, and not much oil. This was just before going back to the dyno after curing some minor spark retard at wot. Just rinsed them off in gasoline and lightly wire brushed them off and checked the gap and reinstalled. They only had 20k miles or so at that point and since they were platniums didn't see any point in buying new ones when these looked fine at the time.

 

It's using a little oil,nothing to worry about.

 

Wire brushing is not a good idea..... it leave residual metal on the insulator, reducing the effectiveness of the insulator. Only way to clean them is with a sand blast.

 

I did not realize that, it was just by hand, maybe less than 10 strokes with a hand wire brush, enough to clean the discoloration off, but I see how that may effect it. Something my dad used to do if they were still good looking plugs, not that he was a motor head though or anything.
I'll keep a closer watch on these, but yes it does burn oil as mentioned earlier, about a qt or so every 1200-1500 miles.

 

Are your heads ported? The port job on my LE2s cuts in slightly to the rocker arm stud holes, allowing oil to leaking into the intake ports. My plugs looked exactly like those after about 20k miles.

I put black RTV on the threads of all the rocker arm studs and no more problems. You should probably also check out valve guides and seals.

 

No the heads aren't ported, but I bet the rocker studs don't have any sealant on them. I'll be swapping the springs out soon so I'll definitely check that when I do, the heads were given a 3 angle valve job when they were apart and getting new springs for the LPE cam. Thanks for the tip there.