I have a '91 Pontiac Sunbird. Modified 2.0 OHC TBI. When you start the car 1. It starts and fires fine but just keeps turning over. 2. when you floor it however it starts to start running but bad and when it does finally fire and you rev it it will shoot al alot and i mean alot of black smoke out of the exhaust and occasionally white smoke, then occasionally it will idle down and idle fine. NO i don't have the can seen on there anymore know that wasn't helping matters. It also feels like it has no power. I was told that it may be the Catalytic Converter but i don't want it to be as this is expensive. Could it be there is another oxygen sensor under there by the cat. that has gone kaput or...Please help I don't know if this is bad or just not good.

There isn't another O2 sensor behind the cat, and if there was it wouldn't affect performance anyway. Have you done any work to the car lately or did this just happen on it's own? Has it been gradually getting worse or did it just happen overnight? Check obvious things first (like spark plugs, plug wires, fuel filter.. ect.) and then go from there. Pull the codes out of the computer if you can. If you try to explain the problem a little better I might be able to help a little more also.





You can't outrun the radio.

ok thanks. I was told the cat needs replacing the and i know it has needed a 'tune-up' since i bought it. I am going to try that.
Thanks

have you checked the vaccum hose going to the map sensor, I usually trouble fuel filter, vaccum hoses, Then look into see if you got an check engine light on.