My 98 z28 is sluggish in every gear when it's below 3000 RPM. It backfires and just doesn't have a lot of power. Once it reaches 3000 RPM it takes off and runs smooth with no backfiring. I used an OBD II tester and it says there is no activity in both o2 sensors so I'm going to replace them, but that can't be the only problem. Does anybody have any ideas as to what it could be? Thanks.

 

If it is the o2 sensors thats why the car runs like poo. You need to change them out.

You could have a blocked cat, or need new spark plugs but do one repair at a time to rule out what the problem actually was/is

 

I would definitely change the sensors first. Also, clean the mass airflow sensor. I cleaned that and it did run a little better. But my main problem (and yours sounds similar to mine) was the fuel pump. Had no power, backfired, ran horrible under 3000rpm.

 

start with your 02's, if that doesn't fix the problem pull a plug and check it out see if it is wet or anything. the best way to eliminate problems is start with what your scanner says. then I would say from there, if it doesn't completely narrow down the problem to start with the cheapest thing to fix and work your way to the most expensive. and don't forget to test everything before you buy something. 20 extra minutes spent testing/inspecting can save you a lot of time and money in the long run.

 

I changed the o2 sensors and cleared the codes. Then I took it for a quick drive and used the tester again... it's still saying both o2 sensors have no activity. I checked the wiring and everything seems intact. Does anybody have any idea what would cause this?

 

have you put a volt meter to the wires and make sure you have a completed circuit?