I'm having problems fowling plugs. The first set was AC Delco FR3LS, which is what AFR recommended as a starting point. After a few hundred miles, they started missing. I pulled them and there was a black deposit on them (it's been awhile and I don't remember exactly what they looked like). I thought that they weren't hot enough to burn off deposits, so I went up to an FR5LS. Now, after a few hundred more miles, they have a white deposit on them, indicative of the plugs being too hot. On both sets, I had them gapped to .035.

My fuel pressure is OK, but I don't have access to a Diacom or A/F meter to see if my mixture is stoich. The only thing that comes to mind is the fact that I'm using Disc style injectors (Lucas), rather than the more finely atomized pintle style that most people use (stock, Ford, Accel, etc.). Possibly this could be a reason the entire mixture isn't burning (if in fact it's not)?

I've been researching this issue and have come up with some possible solutions. Since I am running a hotter coil and better wires (both MSD), I should be able to gap the plugs to .040. Does this sound like a appropriate?

I'm switching plugs to NGK V-Power plugs, with a 7 heat range (coolest is 11, hottest is 2). I crossreferenced this heat range plug and found it to be equivalent to an AC FR3LS.

I do have a question about cutting back the electrodes on these NGK plugs. From research, I learned that part of the improvement of cutting back plugs has to do with the fact that the spark jumps to a sharp cornered surface easier than a flat one. On a standard plug, the ground electrode is cut back to the outside edge of the center electrode, allowing the plug to be gapped in the "optimal" spot for the spark to arc to the sharp edge of the center electrode. However, the NGK plug has a "V" groove cut into the middle of the center electrode, running parallel to the ground electrode. I believe that the V shape negates most of the improvements seen in cutting back the ground electrode, since there are 2 sharp corners running the entire length of the center electrode for the spark to arc to.

I'm about to post some pics, but my service is screwy right now, so when it gets going again, I'll post a couple of pics of 2 spark plugs I pulled the other day from #2 and #3 cylinders.

 

Keep in mind these were put in about 800-1000 miles ago. Here are the pics:






[Modified by dtorc4, 9:52 AM 3/31/2004]

 

Well to start Smokey said there's nothing to gain by more than a 0.045" plug gap for the performance electronic ignitions - MSD (etc.). But a stock system may not have the power for large gaps. Dr. Jacobs says most hot street performance motors only need maybe one heat range colder plug than stock. Full race motors that run WOT can use colder plugs but not for street cruising. :nono:
I was surprised once to find my spark plugs where shorting due to bad wires. Headers can burn up a new set of wires fast. Do u have shielding for ur wires at the headers? Even stock systems came with heat shields for wires on the C3. If the missing problem gets progressively worse I suspect the wires are bad. :yesnod:

 

Yes, I do have the high-temp cloth material wrapped around each of the spark plug boots. The missing doesn't seem to be getting any worse, but of course this has only been a couple of weeks. I got some new plugs and I will change them out today and see what happens. I will also reset my idle.