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Discussion Starter #1
2006 GTO Automatic. Stock. 145,000 miles

4/2016, 102,000, replaced Spark Plugs with AC Delco AC Delco 41-110 and Spark Plug wires with AC Delco 748RR
9/2017, 119,000 replaced front O2 sensors with AC Delco part 213-1568

Need your opinion if my fuel pump needs to be replaced. I have been getting these codes:
P0171 Fuel Trim System Lean Bank 1
P0174 Fuel Trim System Lean Bank 2

Last night both got set and P0300, Multiple misfire

To spare the long read, I discuss the O2 troubleshooting efforts later in this post.

This morning I checked the fuel pressure. All measurements were done with the engine off. I tried to follow the FSM.

After sitting 11 hours idle the fuel pressure was 0 psi
Put the ignition on: 50 psi
Turn off ignition: 40 psi

Tried 2 other times with these results:
Ignition on: 52 psi
Ignition off: 42 psi

IAW the FSW, tried to bleed it down and check. The closet I got was 7 psi. Waited a few minutes and it down to about 5 psi.

Do you think I should replace the fuel pump? I have no reason to believe it has ever been replaced.


O2 Sensors:

Before Christmas got these codes:

P0171 Fuel Trim System Lean Bank 1
P0131 Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
P0174 Fuel Trim System Lean Bank 2

I replaced both O2 sensors with AC Delco 213-1568/GM 12569429.

All was good for a couple of weeks then I got:
  • P0171 Fuel Trim System Lean Bank 1
  • P0131 Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)
For Christmas I got Bluetooth Scan tool that works with my smart phone.

Driver side O2 sensor was dead at 0 volts
Passenger side O2 always moving between 0 to 0.8 volts

1/12/2020 Swapped O2 sensors between driver and passenger sides:
  • Driver side O2 (old passenger) always moving between 0 to 0.8 volts
  • Passenger was holding a steady 0.4 volts and bank codes were being set
A week ago installed a new O2 sensor on passenger side:
  • Driver side O2 (old passenger) always moving between 0 to 0.8 volts
  • Passenger side was holding steady voltage
Yesterday driving home got these codes
P0171 Fuel Trim System Lean Bank 1
P0174 Fuel Trim System Lean Bank 2

  • Driver side O2 now was holding a steady 0.3 volts
  • Passenger side O2 was holding steady 0.7 volts
Over the past couple I have done visual for obvious sources of vacuum leaks but I did not dig deep. I have new DENSO 2344668 O2 sensors on order but I think I may have a fuel pump problem.

Opinions?

Thanks in advance
 

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Then that's one dirty as smurf MAF.

Usually still will get o2 response as the ECM trims. You'll see some abnormally high fuel trims, and if they are high enough they will set the lean codes.

It would have to be so far out of wack that the ECM can no longer compensate by adding trim.

Even if was the case, the o2 sensor readings don't make sense. One is reading slightly rich, the other slightly lean.

I would do some data logging if you could.
 

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Discussion Starter #5
Then that's one dirty as smurf MAF.

Usually still will get o2 response as the ECM trims. You'll see some abnormally high fuel trims, and if they are high enough they will set the lean codes.

It would have to be so far out of wack that the ECM can no longer compensate by adding trim.

Even if was the case, the o2 sensor readings don't make sense. One is reading slightly rich, the other slightly lean.

I would do some data logging if you could.
Here are a couple of log files I was able to get today. Represent about 50 miles since I reset the PCM. I check the fuel pump pressure with the engine running and it was a solid 62 psi. Cleaned MAF and temporarily installed a known good MAF - no difference.

Thanks
 

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