Running a little rich...

[Billy Mild]

Those black spots are coming from the ZR-1 when it is started up cold. I have also noticed it smells a bit rich too. The car still has cats, Borla axle back and deleted center resonator.

I have heard it has a custom tune, but he chip appears to be stock.

[A26B]

If that continues at startup, it may be an injector housing gasket leaking coolant into an adjacent cylinder.

[Billy Mild]

Originally Posted by A26B

If that continues at startup, it may be an injector housing gasket leaking coolant into an adjacent cylinder.

Not the answer I was expecting. Which injector housing gakset, housing to the head, or plenum to injector housing?

[A26B]

To the cylinder head. The top side gasket of the injector housing is normally referred to as the plenum gasket.

[A26B]

Afterthought: if the injector housing gasket is the source of a coolant leak, it will be into any of the front 2 cylinders on each bank, i.e., cylinders 1&3, 2&4.
A quick & simpler check would be performed on a cold engine after full warm up. Remover the plugs on the cylinders mentioned, pull the fuel pump fuses( both primary & secondary). Have someone crank the engine over & look for coolant blowing out of a cylinder. It won't be continuous, just a quick puff.

[RussMcB]

Probably silly thought: I wonder if someone could analyze that soot and tell its source (coolant/water, fuel, ...)

Maybe looking at the plugs would provide more clues, especially if 1 or 2 look odd while the others look good.

[A26B]

Originally Posted by RussMcB

Probably silly thought: I wonder if someone could analyze that soot and tell its source (coolant/water, fuel

Sure, get some on your finger & stick it on your tongue. Sweet - coolant if anti freeze present, fuel-you will know, nasty.

I could never see it on the plugs because the amount was small and it only appeared in the exhaust at cold startup.

[XfireZ51]

The plugs could also look steam cleaned.

[Paul Workman]

Originally Posted by XfireZ51

The plugs could also look steam cleaned.

Yeah! Nothing like coolant blowing a hole through a thin (ported) spot in the injector housing to steam clean the entire top-end!! (ask me how I know...)

[Billy Mild]

Another pic.