2007 suburban 5.3 running rich

[jcwilliams]

I have a 2007 suburban 5.3 flex fuel engine. Has p0172 and p0175 both banks running rich.

 

Fuel alcohol is at 76% on regular fuel.

 

I've had two shops with snap on scanner not be able to get in there and reset that parameter.

 

Long term trim is pegged at -19%

 

I'm at a loss other than the dealership...

Any ideas?

Thanks

James

[Jsdirt]

I hear there's an alcohol sensor in the tank that fails. If you've never run E85, and are sure you have a tank of regular (someone hasn't borrowed the truck), that sensor could be the cause of the richness. If the computer expects 76% and actually burns regular unleaded at 10-15%, it'll run pig rich.

[jcwilliams]

I hear there's an alcohol sensor in the tank that fails. If you've never run E85, and are sure you have a tank of regular (someone hasn't borrowed the truck), that sensor could be the cause of the richness. If the computer expects 76% and actually burns regular unleaded at 10-15%, it'll run pig rich.

From what I've read starting in 2005 GMC vehicles measured the alcohol % based on fuel level in the tank o2 sensor voltage and canister flow....

I called the dealership with the Vin and they don't have a flex fuel sensor or a alcohol sensor listed for it...

[Jsdirt]

Was just reading that on ones without the sensor, the fuel level sensor is part of the algorithm calculation of alcohol content. Also, short trips after switching from E85 to regular, or vice-versa, will cause issues too, since the computer can't learn the alcohol content - needs a bit of time to calculate it, apparently.

 

The computer will attempt to relearn alcohol content after detecting 3 gallons or more of gas added to the tank. Could try topping it off & going for a long drive, or, if you don't have an emission test coming up soon you can disconnect the battery for a half hour or so, and reconnect, and see what happens. Maybe it will default to regular.

 

This guy had the same truck, same exact problem - some good info here: http://www.obd-codes.com/forums/viewtopic.php?t=9419

[jcwilliams]

Was just reading that on ones without the sensor, the fuel level sensor is part of the algorithm calculation of alcohol content. Also, short trips after switching from E85 to regular, or vice-versa, will cause issues too, since the computer can't learn the alcohol content - needs a bit of time to calculate it, apparently.

 

The computer will attempt to relearn alcohol content after detecting 3 gallons or more of gas added to the tank. Could try topping it off & going for a long drive, or, if you don't have an emission test coming up soon you can disconnect the battery for a half hour or so, and reconnect, and see what happens. Maybe it will default to regular.

 

This guy had the same truck, same exact problem - some good info here: http://www.obd-codes.com/forums/viewtopic.php?t=9419

Yea I've read through that forum also.

I'm in Ohio so no emissions testing here. I've tried resetting computer with disconnecting the battery and fuel trims reset for a while then went back to -19 again. Alcohol % I can't seem to get reset. Since I've been messing with it its been through on long trip to Michigan and 3 tanks of fuel in 2 to 3 weeks so if it was going to reset I would of thought it would have done so by now... Idk I'm lost.

[Jsdirt]

I hear ya. Gotta love electronics.

 

Has to be something between the fuel level sensor, o2 sensor, or EVAP system ...

 

Sorry I wasn't much help here. Thanks GM!