Was following my daughter and her 69 Charger 440 home the other day and noticed black smoke from under car, not excessive but noticeable. Freeway speed. It's the original engine, 130Kmi, never rebuilt and never abused (I know the previous 2 owners). 440 starts and runs good, idling a bit rich. Gonna put the AFR gauge on it to quantify. No smoke at all at startup/idling.

Got home and noticed a leaking power steering cap, so thot maybe at speed PS fluid was mixing with hot engine. Anyway, fixed that but smoke persists. Rear bumper/lower rear panel is a bit sooty.

Some sort of PCV issue or ???

idling a bit rich

Clue

'Some sort of PCV issue '

that would be my first thought. pull it and shake it, you should hear a rattle. if not then it's clogged and needs to be either cleaned or replaced. repro ones are pricey if that matters to you.

are you able to smell the exhaust? if its rich it can burn your eyes and of course leave black soot.

black smoke is running rich.

bluish grey smoke is burning oil

white smoke (steam) is burning water/coolant

I don't know about a rich idle.
As the black smoke was seen while following the car.
Maybe a miss fire.
My guess, the carb. needs attention.

PCV is clean, looks ok, rattles. Some oil puddles after sitting for awhile, and lower engine/trans area is pretty oily. Could this be the "smoke" after engine/trans warm up?

pull a spark plug & see how it looks.

Quote"Some oil puddles after sitting for awhile, and lower engine/trans area is pretty oily."
Heavy oil leak on hot pipes could be black.
I don't mean to be a smart Alec but...
Clean it up and solve your oil leak problem first,
then see if your black smoke still there.
You don't want to run low on oil looking for a problem that might not exist.

agreed, possible rear main seal/sending unit IMHO

No offense taken, you are correct...just trying to get a sense of how to tackle this.

Rear main was recently replaced by daughter and boyfriend (heart surgeon who knows his way around engines). I removed 727 view plate and case/converter was pretty clean...wouldn't this area be soaked if rear main leaked? OTOH don't know where this much oil on the floor could come from except for the rear main.?.

Sending unit area looks dry. There is about 50yrs of accumulated grime on the engine block, seaping areas on valve covers and oil pan. Probably need a good pressure wash, then some new valve cover/pan gaskets as a start.

While I'm at it, decision to be made on whether to rebuild orig 440 given age and mileage. I guess some cylinder pressure checks would be a good start (along with checking the plugs).

Check to see if the seal around the trans dip stick is sealing, or leaking.

As said I'd confirm/elim any external leaks. Might be a carb issue: leaking needle/seats or less likely partly waterlogged float(s). once any leaks are eliminated does it appear to be blue or black smoke (or both)?

First thing to check would be the choke. If it's got a vacuum choke pull-off it may be blown. Wire the choke open and see if it clears up.