18 mpg black smoke out exhaust

Ok I have a 1996 RS 420A auto.
I over hauled the engine (bearings gaskets honed the cylinders, new waterpump etc..) and put in crane performance sport compact cams, and JE forged high compression pistons (10.5), titanium valve springs. Everything else is stock.

I get 18 miles per gallon. Black smoke out of the exhaust in high RPM. And the car idles at 1000 RPM and sometimes it goes from 1000 - 2000 RPM. I replaced the O2 sensor about a month back. And i am still getting this problem. Could I have bought a bogus O2 sensor? Wires going to the sensor? Something else?


HELP!!!

Did you have the car tuned at all? Your running extremely rich.

something went wrong in the reassembly?

do a compression/ leakdown test to see...

what do you mean tuned? you talking about the computer?

you probably need to get the engine tuned or tune the engine especially with those new cams

please explain "tune" for me

please explain "tune" for me

There is a search feature on this site, use it.

When they say "tune", they are reffering to the changing of your cars computer, by hooking it up to another computer. From their they can do whatever, but in your case, they would change/modify the air/fuel ratios.

yeah a/f is way out. it could be a simple thing like a sensor, but then too since its been rebuilt, not saying that you dont know what your doing, but like timing could be off. but definitely since you have different cams it needs the computer reprogrammed. i know with saturns that when i hear this problem it normally points straight to the coolant temperature sensor. the cts helped my friends 420a idle better and ran better.

also those cams might make the car idle higher.

b4 you attempt to "tune" it, double check the physical parts of the engine, ie the compression/timing marks/ etc.

doesn't hurt to check for trouble codes too to rule out that coolant temp sensor as well... no signal to ecu from this thing & car's gonna be running in open loop or enriching the mixture to try to get a reading of "warm"