Mixture says lean, plugs rich and Black smoke

[4wheelin]

I've a vehicle that's been doing my head in. It is a 6.6L cast iron Bottom end LS1 with a ProCharger 15 psi and a 235/245 cam on 116. It starts, idles and cruises well at light throttle in closed loop but under load fouls plugs and fumes noticeably on the dyno. I can foul plugs at 13:1 at 2000 rpm around atmosphere, under WOT at 12.5:1 it doesn't foul plugs but they read very rich and fumes black smoke in quite large amounts. I have tried running CL up to about 100 rwkw only going into OL and 13:1 as boost commences and I can get the plugs clean enough to not foul but it's still fumy. The engine is new. We had to replace the intake with a 4bbl single throttle as the FAST manifold had very poor distribution under boost(plugs read poorly previously). It makes 575 rwkW, I have scaled the tune by 30% so I have timing on the MAP. I have tried two different Wide bands, the dyno and a wideband commander and both agree on mixture. The car has a substandard exhaust in a twin 2 1/2. I'm thinking possibly exhaust back pressure too high. The engine is quite inefficient at part throttles, it takes a lot of timing with no detonation, 35 degrees at 2000 rpm at atmosphere. Open to any suggestions. Can't really post a log or the tune as its tuned in HP, I have both, this was already tuned before it came to me with HP but wasn't scaled and had a different engine.

Any thoughts appreciated

[gpr]

If an engine miss fires or is running extremely rich it will put raw fuel and air into the exhaust. O2 sensors will pick this up as reading lean because it is seeing oxygen that isn't being burnt.

From my experience running an 02 sensor in conditions like this for very long is not good on them and will start reading incorrectly. I would try and get the tune as close and reasonable as possible, probably even error on the lean side. then put a new o2 sensor in and try it again.

[4wheelin]

Yes I agree, problem is the vehicles o2 sensors and my wide bands are all in agreement and with the bidirectional control if I push the mixture leaner their is a significant power loss. The tune still behaves the same in open loop.

Cheers

[slows10]

Without a posted log, it is just guess work. Post a log with all the required pids and also showing the wideband.

[4wheelin]

I can only post a log in HP

[joecar]

With your HPT log, can you display LTFT's, STFT's, and HO2Sx1 voltages, along with wideband AFR (or lambda), and take a screenshot of that and post it here.


What fuel are you using...?

[4wheelin]

Yep I can, I don't have a log with wide band as I've been using the wideband on the dyno, the vehicle is on BP98 Its a short log with a power run and the long term fuel trims are disabled, its not a specific run of the problem area though where I get the fouling.

[picnic_george]

It sounds like a coil problem or spark plug problem. Maybe you're blowing the spark out and not burning the fuel under boost. Have you tried another set of coils? What plugs are you running and what gap?

[4wheelin]

I though possibly ignition too but it dosen't miss under full load at 6400 rpm, only part load, it misses when you drive casually and under full noise initially but clears after a number of runs and won't miss a beat untill you cruise it again at part throttles and light (light but above cruise, light acceleration) throttle. The plugs foul all the way down the carbon, I can then do some full noise runs and get them to clean up.

[Woodchukka]

I had an issue like this with a turbo charged RB30. It ended up being caused by a combination of the new iridium plugs I installed (took about 100km to play up badly) and the lower compression of the engine. It caused plugs to foul (jet black) then that caused poor low load performance and lots of black smoke from exhaust. Even had enough fuel going out of the pots to burn in the manifold and start to spool the turbo very early. So what plugs are you running and what is the compression?