2008 Escalade P0455, P0172 & P0175, pulling my hair out.

[93M6Formula]

Also, I did a compression check the other day just to check, passed perfectly with basically all 190 PSI. But I noticed the plugs were all super clean, would they not be sooted up and black if it was running rich? Thye have about 2K miles on them. I also can't say it's actually blowing black smoke and I don't really smell fuel either. Could this be a false rich condition?

 

[B-train]

All the codes listed lean towards too much fuel in the engine and is messing up the desired burn ratio the PCM is looking for. I would highly suggest the vent solenoid in the engine bay (driver side by fuel rail). I think what is happening is your fuel tank is heating up as you drive and that pressure is just venting right to the motor.

The system is designed to do this as needed to make sure the tank doesn't over pressurize. Your plugs look fine as well. If the were sooted up from too much fuel, you'd REALLY know it by the way it would run/not run.

 

[93M6Formula]

All the codes listed lean towards too much fuel in the engine and is messing up the desired burn ratio the PCM is looking for. I would highly suggest the vent solenoid in the engine bay (driver side by fuel rail). I think what is happening is your fuel tank is heating up as you drive and that pressure is just venting right to the motor.

The system is designed to do this as needed to make sure the tank doesn't over pressurize. Your plugs look fine as well. If the were sooted up from too much fuel, you'd REALLY know it by the way it would run/not run.

The confusing thing is, for a week or so I capped off that port on the intake so the EVAP was venting to atmosphere and nothing changed in that time.

 

[B-train]

So, I read through the thread again. Since EVAP didn't seem to be an issue, you replaced the fuel pump, and put in different pistons that you aren't sure of the compression ratio of: have you tried just running 87 octane? Both of my Denalis say "premium" recommended, But I rarely do it. I get smoother running with premium, bit not really any better fuel economy to justify the cost. At different altitudes, it actually runs better with lower octane fuel. Food for thought. I'm out-of suggestions w/o actually seeing or driving it.