P0171 Lean bank 1

bm2004x Sep 7, 2019

  1. bm2004x

    bm2004x Test Drive

    Messages:
    38
    Location:
    United States
    I have an 04 na 3.3L with 190,000 on it. Trying to figure out which route to take for parts. The lean code could be a ton of problems. I have a OBD2 scan readout of the Fuel trims for starters. The O2 sensors all seem to be within normal operating conditions. The Bank 1 seems to be the issue hence the P0171. Short term with start at 0 then drop to -25%. I think that is because the Long term is stuck at 35.7% no matter what, cold start/ idle, 2500rpm....etc. MAF sensor reads normal so not sure that is it. The issues are; possible vacuum leaks, fuel pressure drop, fuel clogs all make sense for numbers fluctuating out of range in Short term and Long term readings or even bad numbers being read on both bank 1 and 2. Im Lost.

    I should mention, the truck runs slightly rough at idle.... little shaky. Its perfectly fine when the load is applied. truck starts and runs. No excessive fuel consumption that i notice. truck has original O2 sensors, cats, MAF and injectors.

    going to try to spray some card cleaner around engine to measure the ST LT readings again.

    The odd thing is the LT bank 1 fuel trim being stuck at 37.5% no matter what.
     
  2. bm2004x

    bm2004x Test Drive

    Messages:
    38
    Location:
    United States
    Ok, I think i have some more diagnostic info. The Bank 1/ Fuel System 1 seems to be in Open Loop Fault mode and the bank 1 sensor 1 (upstream) seems to be staying right at .500V. not fluctuating like the other bank. bank 1 sensor 2 (downstream) also seems to be stuck at .320V but did move at least once to .310V at idle. Im thinking now i have bad O2 sensors?

    Have a pretty rich smelling exhaust so my guess is O2 sensors are fried with 190,000 miles on them. I guess ill throw some parts at it to see if that solves the issue? The computer reading Lean but has a rich exhaust smell must mean the injectors are working and making the bank 1 rich when it really doesnt need to be because of the failed O2 sensor.
     
    JamesN likes this.
  3. bm2004x

    bm2004x Test Drive

    Messages:
    38
    Location:
    United States
    So replaced the passenger side o2 sensors. fixed. The upper one was a pain because it started to back out the threaded bung thats in the cast exhaust manifold. My suggestion is to use 2 wrenches if you need to heat the piss out of the o2 sensor. One on the sensor and one on the bung.
     

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