I have a 2011 GMC Z71 with a 5.3L flex fuel AFM engine, 82,000km and it won't start properly cold. What happens is it seems to flood itself and will not start unless the throttle is pressed to the floor. Then will start, throw a puff of black smoke smooth out and idle at around six hundred twenty rpm. It starts and runs fine hot, uses no oil but is hard on gas now also. It sets two codes and freeze frame data shows it seems to set these codes just after it's started hot. The codes are P0172 and P0175, both banks rich mixture. It doesn't set the codes when the truck is cold in open loop mode, only in closed loop mode. My scanner shows all readings as normal except the long term fuel trim which reads -30% both sides (I can't remember STFT but I don't remember it as being off by much). With the engine off the ECM voltage shows 11.6 volts which seems a little low. Running it shows around 12.7. When it ws started cold once it showed MAF at 1.12 lb/min at 627 rpm which I thought was high but warm it dropped to .67 lb/min which I would say is normal for that engine at that speed.
One person I talked to thought the engine might think it's running on over 70% ethanol, there seems to be a history of some of these engines doing this. This engine has never seen more then 10% ethanol as far as we know, it has made two trips to Mexico and may have accidentally been fueled up with high ethanol blended gas. But it should have returned to low ethanol settings when it was fueled with regular gas I would think. There was actually a fuel pump issue on one of these trips. He added some oil to the fuel and it cleared up until last month when the fuel pump acted up again. When I put my scanner on it then there were ten codes including some for fuel flow and pressure issues and the two I listed above. The scanner showed 9psi KOEO and 0psi KOER, we replaced the fuel pump and now it shows 43psi most of the time with the pressure climbing to 60psi once that I noticed.
Anybody have these symptoms and solved the problem? If you have please let me know. Myself and at least three others I've discussed this with will greatly appreciate it.
Thank you.
One person I talked to thought the engine might think it's running on over 70% ethanol, there seems to be a history of some of these engines doing this. This engine has never seen more then 10% ethanol as far as we know, it has made two trips to Mexico and may have accidentally been fueled up with high ethanol blended gas. But it should have returned to low ethanol settings when it was fueled with regular gas I would think. There was actually a fuel pump issue on one of these trips. He added some oil to the fuel and it cleared up until last month when the fuel pump acted up again. When I put my scanner on it then there were ten codes including some for fuel flow and pressure issues and the two I listed above. The scanner showed 9psi KOEO and 0psi KOER, we replaced the fuel pump and now it shows 43psi most of the time with the pressure climbing to 60psi once that I noticed.
Anybody have these symptoms and solved the problem? If you have please let me know. Myself and at least three others I've discussed this with will greatly appreciate it.
Thank you.
