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]

15771

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?

[4wheelin]

Thats more like what I'm thinking and seeing. The engine is 8.5:1 I've been told by the builder and the cam is 235/245 on 116. I did have Iridiums in it but am now using NGK TR plugs. Were you reading rich or lean? It seems to me like its very inefficient at that point

[Woodchukka]

I could not give you an AFR as I did not have the gear to measure at the time however definitely very very rich. Idle dropped from 750 - 800 down to maybe 400. Engine would only barely idle black smoke billowing from it (with an inspector and cop asking me questions). I think the VL's standard compression was 7.8:1 (which mine was). NGK rep said he had never heard of it before however spoke to a tuner and they had the issue often and said that if you use the iridium's you needed to go 1 or 2 heat ranges hotter (depending on engine) as they would foul at low loads every time. He said standard compression they were fine however lower compression turbo applications he said to avoid them. After a lot of searching through the VL's fuel and ignition circuits and finding nothing of value (in tank lift pump U/S but fitting new one did not help) I gave up and fitted $12 worth of new spark plugs (only ones I could get on a Sunday arvo. Was running NGK-R's) and problem was forever solved (did this before I spoke to people). The plugs were all fouled to the same degree and it was like they had been painted mat black.

[4wheelin]

I'm not running Iridium plugs now and still have the issue, shame you didn't see the mixture. I think it may be somehow related to the largish cam and lower compression, I have customers with VL's that run 9's on ETs with low comp and big cams that don't have this issue though so still confused. The mixture is definitely not rich by AFR's but is visibly smokey and fouls plugs. I believe it is an efficiency thing.

[Woodchukka]

Yeah only got my hands on that sort of stuff recently. To ask the silly questions the fuel pressure is ok and the injectors are not leaking? Maybe try hotter plugs? Hope you figure it out soon.

[4wheelin]

Fuel Pressure is good, you'd. I did go from 7-6 in the NGK, catch 22 too cold when part throttle too hot under full load

[Woodchukka]

I don't claim to be a guru on the matter however I see it best to at least try the original heat range with a plain jane plug (my issue was fixed with a cheap set of champion plugs) and see if it fixes the low load fueling issue. If it does then attention can be turned to the issue that they may be too hot under load however I have found that usually these issues are best restarted from a known point. In this case the standard heat range. Wind up slowly and see how hotter plugs hold up which likely means pulling them after a run or two.

[joecar]

For boost you shouldn't really be running platinum/iridium plugs (the tip is very fine and does not shed heat very well)...


try something like NGK TR6.

[4wheelin]

Not running Iridium.

[gagliano7]

I had a coil go bad that would work fine under full throttle but idle and part throttle coil didn't work correctly. I took a temp gun and checked each header temp and found #8 was 180 * cooler than the rest. Replaced coil and been good ever since.

[FirstGenThree]

Might it be worth running a lower octane fuel (and staying out of boost) to see what effects it has on this issue? Just for reference, have you checked compression to see what this engine cranks at with such a large cam/low static comp? Also if you're still concerned about the exhaust being restrictive, check the pressure, if you don't have the tools a local exhaust shop should have (for the purpose of checking for a plugged catalyst). With all the issues so far, this hasn't "made oil" has it? If it were running rich enough to get significant fuel passed the rings the cylinders could be getting washed down. Simple to check the oil and make sure it isn't overfull nor smells like fuel. Don't overlook the basic mechanical stuff just because it's a hipo setup. ...Just some ideas that may give insight as to if this really is a tuning issue or something else.