1996 F-150 4.9L

So I did a drive cycle after changing the battery and no lights are coming on. But I'm failing my emissions tests in Oregon.

I'm getting p0133, p0420, p0171, p0174 warning lights. So, in that order: O2 Sensor Circuit Slow Response - Bank 1 Sensor Sensor 1, Catalyst System Efficiency Below Threshold - Bank 1, System Too Lean - Bank 1, System Too Lean - Bank 2.

Originally it was all my O2 sensors failing, which of course was faulty. Had the computer replaced, and one O2 sensor. Worked and passed DEQ. Now I'm at a loss. I replaced another O2 sensor and that didn't fix it. Ran it hot for an hour before testing. Like 70-80mph on the highway to get er cooking.

Not sure what to do. Any tips for a rookie? I've done a lot of basic stuff (new solenoid, changed starter, changed alternator, swapped some battery cables, etc.). But I can't seem to figure out why I'm failing emissions. Got some injector stuff to put in, just haven't done it yet.

Thanks folks!

 

There are plenty of different issues that can cause oxygen sensor codes to show up. I would start by pulling a few spark plugs and see if they indicate a lean condition. If they do, then find out why it's lean. If they don't, check for exhaust leaks and electrical problems with either the o2 sensors, or their circuits. And don't assume that anything is good just because it was recently replaced.

 

Most likely your catalytic converter is toast because the truck has been running lean. However, you need to verify the lean condition is present because its possible the oxygen sensor is getting faulty data due to an exhaust leak (EGR or Exhaust Manifold possible). If you confirm it is running lean, either by checking the plugs or the fuel trims, you'll have to figure out whether its getting too much air, not enough fuel, or both. You'll need a vacuum gauge and a fuel pressure gauge.