As stated, i have the stock D16A6 in my '90 CRX Si. It's been smoking a very dark grey/black for a since i got it almost a year ago at high rpms(noticable above 5000) in free rev, or when i go WOT in gear. Its increased since I've put on a header and high-flow cat, obviously. I've put new Denso iridium plugs, MSD plug wires, new battery, its supposed to have a new dist. cap and rotor. I'm thinking it could be an oxygen sensor going bad b/c its kinda running rich, but its not tripping any codes. Also adjusted my timing from what i believe was 4º retarded to about 1-2º advanced. Any help is greatly appreciated.

 

black is unburnt fuel, running rich. hows your milage? i would try the o2 first, should hopefully solve it. youve been driving like this for a year???

 

my grandparents sentra burns a quart of oil every 60 miles, has really bad black/dark grey smoke... you change your oil regularly?

 

Yea, it's gotten a little worse since I've had it, but it's mostly at high rpm. I have noticed the gas mileage kinda going down some, but I haven't been keeping track too much lately.

 

Black smoke is running rich, blue is oil. Try changing your O2 sensor, it's easy to do and it's like 10 bucks.

 

well, i think u need a full tune up.. change of oil, and while your at it, try checking your rings and pistons to see how faaked up they are. if it is a high mileage engine, it would definetly benifit from a re-ringing. try getting some b-12 chemtool and dump that in an empty take and filler up. also put it in the oil fill and run it for 5 mins at ilde. then drain the oil and see how much crap falls out the drain hole.

you should also try changing the pcv valve and maybe your fuel filer and charcol canister.