I think I have a dead manifold cat... :(

[Shizukesa]

Having some exhaust issues and I'd appreciate some advice.

O2S11 is jumping between 0-0.800
O2S12 is sat around 0.050
O2S21 is behaving like O2S11.
Just installed a cat back last week and it was fine for a few days then all of a sudden a drop in power and a quieter sound. I’m unable to scan O2S21 but I can see it in the live data as previously stated. Oddly... there are no engine codes. Any ideas? Failed pre-cat? Thanks!

[Mihanicos]

When the engine is not sufficiently warm, the ECM uses internally stored default values for the fuel trims. This is open loop operation.

When the engine is hot and a preset coolant temperature is reached and the O2 sensor is hot enough to give a good signal, the closed loop operation comes into effect and the O2 sensor is used to adjust the air to fuel ratio. The base line for both short and long term fuel trims is 0%.

Lean conditions are represented by positive values and rich by negative values. Fuel trims are generally considered good if they are within + or - 10%.

Most manufacturers will set a trouble code when the fuel trims either or individually achieve a value grater than 20% for a prolonged period of time. Wrong engine timing will influence the fuel trims.

 

Chris.

[Shizukesa]

On 4/28/2020 at 7:35 AM, Mihanicos said:

When the engine is not sufficiently warm, the ECM uses internally stored default values for the fuel trims. This is open loop operation.

When the engine is hot and a preset coolant temperature is reached and the O2 sensor is hot enough to give a good signal, the closed loop operation comes into effect and the O2 sensor is used to adjust the air to fuel ratio. The base line for both short and long term fuel trims is 0%.

Lean conditions are represented by positive values and rich by negative values. Fuel trims are generally considered good if they are within + or - 10%.

Most manufacturers will set a trouble code when the fuel trims either or individually achieve a value grater than 20% for a prolonged period of time. Wrong engine timing will influence the fuel trims.

 

Chris.

Hi Chris,

Thanks so much for this. Mine were within the 10% tolerance so I guess I'm just being a worry wart 🙂

[ColinBarber]

If there is a definite drop in power then something must have happened, and whilst it could be the pre-cats breaking up and partially blocking the exhaust that would be a bit of a coincidence. I would start my investigation with the things that has just been change e.g. has the back box failed and clogged?

[Shizukesa]

On 9/27/2020 at 9:25 PM, ColinBarber said:

If there is a definite drop in power then something must have happened, and whilst it could be the pre-cats breaking up and partially blocking the exhaust that would be a bit of a coincidence. I would start my investigation with the things that has just been change e.g. has the back box failed and clogged?

I already sorted it by replacing the main cat and rear o2 sensor 🙂 Everything seems to be fine now!