I'm running a 749 ecu on a supercharged TBI v8 and have been struggling with the tune. A recent compression test revealed a broken valve spring so I figured that was my problem all along. Well, after replacing all 16 valve springs and seals, it's running better but my plugs still don't look right. The porcelain gets a burnt area at the tip on every plug.

The attached picture shows a plug with less than 50 miles! Any ideas what could cause this?

 

It looks a tad lean

 

Yeaaaah.....I definitely agree on the lean part..hope you're not driving it much like that! Or if you do, crank that boost down to nil! On boost, that'll mess some stuff up right quick

I can't help but wonder if maybe the plug heatrange is too hot there.....

 

Well...only 50 highway miles and the WBO2 doesn't show a lean condition. Also the BLMs reported by the NBO2 don't indicate lean. The burnt area on the porcelain that concerns me. I'm running Vortec heads with R44LTS plugs and a MSD 6AL. Plugs are currently gapped at .050. Could it be gapped too wide & the center electrode is arcing to the side???

I tried R43LTS plugs, but that was before finding/fixing the broken exhaust valve spring. Might be time to try them again.

 

that's a big gap for boost by the way. i thought it should be around .035 with boost? that's what we're told for nitrous at least.

 

Yep...you're right. Don't know what I was thinking trying .050 gap. Must be fond memories of my previous 4th gen LS1!

I replaced the plugs with one range cooler and gapped to .034. I also installed new MSD 8.5mm wires at the same time. I still have the burnt area/deposits on the porcelain. I'm going to back off the timing some see if that helps.

 

Just in case anyone else runs into the same problem....I found the solution.

I read some advice in another thread about checking to see if the deposits on the porcelain (what I thought were burned areas) faced the intake valve. If that's the case, then oil is being pulled into the intake from a failed intake gasket or pcv system.

Sure enough, the deposits on my plugs all faced towards the intake valve. I determined that my "stock" PCV system was sucking up oil under boost.

I put a K&N breather on the passenger side valve cover and an oil separator between the PCV valve and the vacuum port on the throttle body. That's it, no more deposits on the plugs! And she's running much smoother now.

 

I would need you to take a picture of the plugs electrode with the elbow facing the camera to know if your heat range is right. There will be a noticable line that once the heat range is correct will end up right on the elebow of the electrode.

Also with running the s/c, consider moving upto a race plug with a cut back electrode for a more direct line of fire and less chance of being blown out when at WOT. You could grind the electrode your self so the end of it is centered on the tip of the porceiln, but it's just as easy to buy the plugs. Found the cheapest AR plugs from O'reilly's for only $21/set, I paid $37 at Perfeormance Auto and $47 at our local wholesaler for the same exact plug!! So call around.

 

IHI, thanks for the suggestions. I put in a set of new plugs this weekend and cut back the ground straps as you indicated. I'll run them for a bit and then do a good WOT run and check for the mark on the ground strap.