06 GMC Yukon 5.3 flex fuel p0172 p0175 codes

[Keele8]

I have an 06 GMC Yukon 5.3l engine, with the flex fuel option. I'm getting a p0175 and p0172 codes. I have read a ton of info on these codes. Cleaned the Maf sensor, no change, replaced the Maf, no change. Fuel pressure is 62 and holds pressure when engine is turned off. Short term fuel trim is 0 to - 2 at idle. Long term fuel trim is -90 to -100. Air fuel ratio shows 11.1. O2 sensors seem to be switching fine. Map sensor shows correct readings, coolant temp is good as well. Can't find any vacuum leaks. Put injector cleaner in tank. Taken it to a mechanic as well, they have no idea what's wrong. When driving it feels like I'm always driving in a head wind, sometimes the idle is rough other times it's not. Seems to run better with the Maf unplugged. Gas mileage has gone down a lot as well. Any ideas?

[Artey72]

Catalytic converter stopped up.

[Keele8]

Not sure how you check that but the mechanic shop I took it to said the cat is fine.

[Artey72]

Well... You can pull o2 sensors and see if it changes anything. It can't burn the fuel if it can't get rid of the exhaust thus the rich codes. I bet if you go to wide open throttle while driving you would end up with mass airflow code. It sounds like to me it just can't breath.

[Keele8]

I've had it at wide open throttle multiple times. The only codes that will pop are the two codes listed, indicating a rich condition. Also got a new air filter when the maf was cleaned. Everything is s stock on the car, no aftermarket filter or anything. Everyone I talk to is baffled.

[txab]

Since you've got a flex fuel vehicle, read through this.

 

 

http://www.gm-trucks.com/forums/topic/78169-e-85-refueling-events/

[Keele8]

Great info, I appreciate it. I've never used e-85 so I'm not sure I'd this applies to my vehicle or not?

[Artey72]

I say again ...exhaust. If it were in my stall with said complaint and symptoms, I would be putting converters on it.