What's is going on with this plug?

Let me start by saying that I know this is no way to read plugs, but it seems like something is off enough here to know without having to do the run wot then shut down method lol

Finally set the car back up for boost/pump gas. Running ok, but still figuring out the tune. Did a few part throttle runs and cruised it a bit. I purposely set the target AFR pretty rich to be safe so i expected the plugs to be a little fouled up. It was richer than I wanted (but directly after a 40-50% run they seem to clean up and have a nice gold color so I think it's mainly part throttle/idle fouling them). One thing I am noticing consistently though is when I pull the drIver's side plugs , cyl 3 is always very lean looking on the strap and has a clean, white porcelain with no fuel soot. This is true if I pull it after a 40-50% throttle run or after a normal cruise. It's an Indy single plane with a FITECH 1200 up top and a EV blow through hat. Running about 7 PSI now with the procharger. I'm worried about doing any WOT testing but no sign of speckling that I can see so it doesn't even seem like it's detonating. There is still color around the top ring but nothing I can see on the porcelien (though I need a good plug flashlight).

I figured there could be some fuel distribution issues at a cruise with the single plane , but THAT much to where all the other plugs on that bank are black? I'll pull all the plugs tomorrow for a better look.

The motor is talking to you on this subject
Is this a SB or BB motor?
Why run it rich at part throttle cruise?
How much timing and what heat range and brand of plugs are you using now ?
Won't the MAP sensor, are you using a two bar or three bar MAP?, tell the fuel controller to enrichen when boost is applied?
Are you using a aftermarket O2 sensor system to tune with or are you using the one included with the Fitech system ?

Number 3 plug looks correct. I can't see the ground wire close enough to see the timing Mark but that appears pretty close for pump gas, although on boost I'd want the mark to be no lower than the middle of the curve and maybe just up around the bend.

I can't see the fuel ring in the bottom of the plug either. The other cylinders are rich everywhere if that is what they look like at a cruise.

The question is are 1,5 and 7 rich or is 3 lean? IMO, I'd say cylinder 3 is right and the other three are rich. The next question is why are the three not like the other.

What does the even side look like...number 3 or 1,5 and 7?

I'd also like to see the fuel ring on number 3.

Right click the image into a new tab. It will show full size;
https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/download/Number/326877/filename/IMG_4882.JPG

At this point, I wouldn't consider #3 "Lean". Just less rich. Looks like a fuel distribution issue, but I think you need some tuning done on the carb first.

He runs EFI and my carb plugs look perfect those not so much............

I would check to see if #3 is even firing. Plug or plug wire possibly ?

If you have a misfire it will really through the AFR reading for a loop. A dead cylinder pumps air into the exhaust and it will skew your readings, in something that can self compensate it will over fuel to try and get the average right to compensate for the one cylinder pumping air, and cause the other 7 cylinders to be overly rich.

I ran into this over the weekend with a friends car. A 68 Barracuda with a turbo G3 hemi. The car was obviously rich and was down on power but the ECU showed it was lean and it was kicking in 15% more fuel to try and compensate. Turns out it has a wiring problem, or ECU problem that is causing the #5 coil not to fire so it is just pumping air and raw fuel into the exhaust stream causing it to read lean.

Like everything in the hot rod world, things fail, break or don't always play nice but hopefully you'll get it figured out..........

Thanks for the replies guys! I'll try to answer a few of the questions, and is it worth trying to post a data log of the car driving? I can do that, just have to figure out how to upload the file.

First, to address why I had it rich at part throttle, it wasn't intentional but I'm very new to EFI tuning so I stuck to most of the idle/part throttle presets in the fitch which I hear tend to be rich. With the Fitech you are setting target AFR's at given points to make the curve but those points aren't adjustable. For example, to set my target AFR at 8PSI at 6000rpm's I have to set a target AFR for no boost at 6000rpm's and for 11.6 PSI at 6000rpm's in such a way that I meet my desired AFR at 8PSI. It takes a little trial and error (or graphing it out, which is beyond my skillset lol). This might better explain what I'm saying: http://fitechefi.com/faq/afr-targets/

I am also running into a little bit of a lean tip in with aggressive throttle input, which causes my AFRs to overcorrect rich (into the 10.9 range) briefly before getting back to targets. This seems to be a common problem and I'm working on fixing it through the tune.


I'm not surprised it's running rich though, I knew I'd have to lean everything out a bit. It's not terrible to the point where it's loading up or anything, it actually feels pretty good part throttle. I don't THINK it's compensating for a misfire, although the Fitech runs off a wideband on the opposite bank and I need to check those plugs out in a few minutes.

I'll check the ignition wire, they are new MSD's but the MSD's honestly are garbage these days. so i'll OHM it and maybe swap it out to another cyl in case the clip opened up too much or something.

IT looks like the plug is firing, the ground strap is white and the base ring has some fuel soot on it. It just looks way cleaner than all the others. I have noticed the idle has been a bit rough, but part throttle feels great and getting into boost felt awesome without a hiccup or a stumble, if it was misfiring it wasn't anything noticeable to me.


I want to take the car to a professional tuner and get it on the dyno, because it's taking me forever to try to tune out these lean tip in issues and it's impossible around here to do any full throttle runs safely on the street. Nearest drag track is 3 hours away.

My main concern is I don't want to go there with a mechanical issue and pay for dyno time only to find out something needs to be fixed first. I guess the best place to check right now is that ignition wire, and pull the other bank to see what those are looking like.

Took all the plugs out, here are the pics. Seemed to even out a little , I leaned the idle out prior to this drive and did a few harder throttle hits (about 75-80%) followed by a short cruise home. Starting to look more like a fuel distribution issue?

I cleaned a plug off with carb cleaner and couldn't find a timing mark, but I am running my timing very low to start because I had no idea what I was getting into tuning for boost. I'll check the logs to see what timing I was hitting on my heavier throttle runs but my guess is, being that I was shooting for a curve with 20 degrees at 8psi, timing was probably in the low 20's at 7psi on the 75+ % throttle runs.

Plugs are Br8es btw , NGK. Here is a pic of the plug I cleaned up.