98 Blazer 4.3L 4wd, throws DTC P0131....low voltage, bank 1 sensor 1. This is after replacement of the fuel regulator and plinum gasket, fuel filter, plugs, cap, rotor, MAP sensor, Throttle Pos sensor, and all three (left bank, right bank pre-cat plus single post cat) O2 sensors and two trips to the shop. Fuel pump holds good pressure and is in spec. I can clear the code and it comes back after about 15 miles of driving.

The first trip to the shop was because it would just up and die and it turned out to be a bad pin connector on the coil. After that trip, it started throwing the P0131 code but still ran okay. I took it back and they said to replace the O2 sensors. I replaced the two pre-cats and it started running really bad and blowing black smoke. I then replaced the after-cat and it ran way better (no black smoke) but still throws the code. It now idles a bit rough.

I removed the cat, it is not blocked and the ceramic was not broken and I cannot hear any exhaust leaks in the exhaust manifold.

My thoughts:
1. A plug has fowled due to the rich mix
2. Wiring to the left bank cat
3. Replace plug wires?
4. Ignition control mod......could this be a problem?
5. Coil going bad?
6. Water Tempurature sensor....could this create a rich mix?

Thanks for the comments.

 

P0131 means the bank 1 sensor 1 is returning too low a voltage. Check the wiring for an open or short to ground maybe?