Lately my car is running like crap, it hesitates if I push the throttle at half or more after 3000 rpm.
I linked it to a scanner and the O2 sensor says it runs lean but when I checked my spark plugs they were covered with black stuff, moreover I can smell fuel from my exhaust.
Wouldn't that mean that my car runs rich?
I changed the spark plugs and it runs better but still hesitates after 3k.
BTW I had sometimes a code 13.

Is my O2 sensor bad?

P.S. I know I need a custom chip to have it run good but I just want it to stop hesistating after 3000 rpm.

Thanks in advance for your help.

 

Unplug your battery for an hour and run the car. Tell us if it drives the same or different (better/worse) above 3000rpm. Make sure you test it within the first few minutes of starting the car - the whole idea is to avoid the ECM going into closed loop mode.

If it runs great for the first few minutes, then goes into closed loop, and proceedes to run like crap, you've definately found your culprit (bad O2).

 

In fact it started acting like that after I changed my intake manifold.
I thought it because it was running lean with the new amount of air so I put 350 injectors and it was running worse with those.
1 day after, the car would barely run so I changed the spark plugs which made it run a bit better.
I put back my stock injectors too.

 

spark plugs can be one reason yes, but the O2 can make your car run just the same as crappy spark plugs would. Change both parts there both inexpensive. Whens the last time the O2 Sensor has been changed?

 

This same kinda thing happened to me last week in even less time. I damn near went crazy trying to figure out what the hell it was. I went over all my vaccum lines, plugs, wires, distributer... and I was near to replacing the ECM and a whole bunch of sensors. The car just kept landing on its face. It felt like a fowled plug (or two), but I'd already been over all that. Believe it or not I found out the plug wires were arching between each other and the chassis. I had discounted this as a possibility at first because the wires are MSD Superconductors and only a year old, but there it was. I raised the hood Sunday night and it was like a christmas tree under there. 12 feet of convoluted tubing fixed it for now, until I can get the new wires.