I need help tuning my LT1 383 in my 95 Z28
I have TunerCAT.
My tune was done by MadZ28 (Ion).
It seems to be quite rich across the board....several black plugs, nasty smelling exhaust.

My question is this:
Using TunerCAT, which tables do I have to adjust to lean the mixture across the board ?
How much should I change the values (as a rough starting point) ?
Which way should I move the numbers ? Up or Down ?
I'm not too concerned with open loop, but am DEFINITELY concerned with closed loop as I drive 120miles round trip (80% freeway at 80+ mph) to work each day, and premium is not exactly cheap !

Any help is greatly appreciated.

Engine specs: 383 all-forged, mild ported stock heads with full bowl blend & comp valve job, LT4 hotcam kit, !CAT, 3.5" exhaust with 2-chamber Flowmaster, New Accel Opti, new MSD coil & new ignition module, MAC mid-length headers.

 

Assuming you don't have a check-engine light that might be indicative of running in open loop all the time, in closed loop the PCM will self-correct the fuel mixture. If the PCM gets outside the range of its ability to maintain a proper fuel mixture, this would cause a trouble code and a check-engine light, unless that diagnostic was disabled.

You don't have cats anymore, and you're running a moderate cam, so this is most likely the cause of the smelly exhaust. With my 350 LT4 conversion with the HOT cam, and no cats, I get rich smelling exhaust at idle, and my tune is pretty much spot on. So, I wouldn't put much weight into this symptom.

Now, the blacked out plugs is a different issue. Keep in mind when you go WOT, your PCM switches to open loop, and uses pre-set parameters for calculating fuel requirements. Most mail-order PCM tuners tend to err on the side of rich because it is impossible to know what the optimal fuel parameters at WOT should be without an analysis of the exhaust at WOT. I purchased a mail order tune for my setup and my fuel mixture was pretty far off at WOT (on the rich side). I picked up 16 HP and 50 LB-FT of TQ by fixing up the WOT fuel mixture.

If your WOT fuel mixture was WAY off, this could cause plug fouling. The only way to know for sure is to do some data logging with wide band O2 sensors, or go to a dyno that has a wide band exhaust gas analyzer (most do). You have made fairly extensive modifications to your engine and it would be difficult to get a mail-order tune that is spot on.

If you have a means of data-logging, I would suggest getting O2 voltage readings at WOT as a start. You should see around 880mv. If it is higher then this, you are too rich, and lower means you are too lean.

You should also try to determine if the plug fouling is happening during non-WOT conditions (e.g. replace the plugs, drive around for a half hour or so, then check them).

 

I should also add that tuning based on in-vehicle O2 sensor readings is not guaranteed to be accurate. The reason the PCM switches to open loop during WOT is because the type of O2 sensor that the factory uses does not work reliably during WOT throttle conditions. However, the O2 sensor readings can be used as a general indicator of how close your WOT fuel mixture is.