black smoke in exhaust - not a 240, but nissan just the same

[Syntax360]

So i sold my 240 to Nathan after it threw a rod and bought a 1986 Nissan 300zx turbo. The only problem w/ her is that sometimes (very rare, and only after car has been on for awhile) when i shift, i give it gas and nothing happens for about a second. i let off for a minute, and i hear the engine come back, turbo spool, etc and there's a puff of black smoke out of the exhaust system. It almost exclusively happens when changing gears. Any help would be appreciated. Thanks guys!

[Cyberkreig]

I dont know how to explain it exactly, but I bet you are running momentarily rich. You let off the throttle and air doesnt flow in to the chambers, but your still injecting based on turbo airflow..

[Syntax360]

i was thinking about the same.....like maybe the air filter is hellaciously clogged (havn't checked it yet....the engine bay is pretty dirty though....16 years will dot that) and when the engine isn't under load and there's just idle vacuum, it's barely sufficient to pull air through the filter. And when i'm shifter gear and i clutch in and hit a low RPM she doesn't want to breath hard enough, but is still shooting gas, and when she does catch her breath there's a small pond of gasoline waiting. Does all that make any sense? I'll check the filter tomorrow and keep ya posted!

[Nathan]

Yeah, you still have the cat on right? I'm guessing if you didn't then you might be seeing fire instead of black smoke at least I hope its just because of the overrun when you downshift. I'm glad everything went through and you got the car!!!

[Syntax360]

ya, it still has a cat....i'll get rid of that when i get the exhaust put on.....who knows when that will be....i'm hoping this rich problem won't clog the cat.....that's all i need

[Nathan]

Well, look on the bright side...at least the smoke isnt blue

[Nathan]

bump...anyone have any other ideas?

[Syntax360]

so i took it to a shop that has built more Z31 race cars than i can count, and it turns out there is too much fuel pressure @ idle and not enough at WOT. It's odd...u gas it and there's a sudden dip in pressure and then it goes back to the same spot it sits at. He said he wants to give the car a good workover cause there's a host of things not plugged in and there are a lot of vacuum lines not routed right. Hope I didn't buy another junker :-(