Replaced upstream oxygen sensor, car runs worse

QUICKTECH

MEMBER
2004 PONTIAC SUNFIRE
2.2L
4 CYL
2WD
MANUAL
120,000 MILES

I replaced the upstream o2 sensor with a new NGK 21045. Since the car has 120.000 on it I figured a new one would be a good idea. The next day car seemed to run great, better than it has in years. The day after it was hard to start and rough idle, loss of power, surging. I did not reset the pcm/ecu or disconnect the battery after install. No check engine light. What could be going on?

1 Reply

ASEMASTER6371

MECHANIC
52,797 POSTS

Good evening,

I would start by checking the fuel pressure. Low fuel pressure will cause this from a weak fuel pump.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

I attached some guides for you to check for low power.

https://www.2carpros.com/articles/engine-has-low-power-output

Roy

FUEL SENDER ASSEMBLY REPLACEMENT

TOOLS REQUIRED
J 39765 Fuel Sender Lock Nut Wrench

REMOVAL PROCEDURE

CAUTION: In order to reduce the risk of fire and personal injury that may result from a fuel leak, always replace the fuel sender gasket when reinstalling the fuel sender assembly.

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1. Remove the fuel tank (4).
2. Disconnect the wiring harness from the fuel sender and the fuel tank pressure (FTP) sensor.
3. Use the J 39765 in order to press down and rotate the retaining ring (1).

IMPORTANT:
- The modular fuel sender assembly may spring up.
- When removing the modular fuel sender assembly from the fuel tank, be aware that the reservoir bucket is full of fuel. The reservoir must be tipped slightly during removal to avoid damage to the float.
- Carefully discard the reservoir fuel into an approved container.

4. Remove the fuel sender assembly.

Image (Click to make bigger)