Where are you reading the AFR, and how do you know if it is closed/open loop? Disconnecting the O2 sensors should have given you a code.

 

It did give me a code and I am reading it off from the Hypertech Powerpac!

 

I was going to have it repainted soon, but I would like see some good gas mileage before I start dropping all that money in it, I was also considering dropping a 402 in it but if there is something wrong I don't think it would be a good decision!

 

for one your afr is not by any means accurate, and if you're considering a 402 i wouldn't be too concerned about fuel consumption by your 5.3.

 

Has anybody changed the fuel filter on the flex fuel truck and where is it, also I wonder if I can have the flex fuel option shut off in my computer?

 

Why don't you talk to a tuner? And why did you buy a Flex Fuel truck?

 

Filter is in the gas tank, it shouldn't need servicing for a good long time

 

I noticed you have in your sig that you have a 180 degree thermstat. These trucks come stock with a 210 thermostat. Running the 180 will make your truck run richer. Richer means bad gas mileage and fouled out O2 sensors. Plus if your gonna put a 408 in you might as well forget all about miles per gallon and start thinking gallons per mile.

 

Agreed on the 408 mileage. But Your Hypertech is NOT accurately reading the AFR unless it has a wideband that can hook up to the exhaust. So you can throw your AFR reading out the window.
You should talk to a local dyno tuner that can hook up to it with real tuning software and they can hook up a wideband and tell you more than that hypertech ever will.
With your 02's unhooked, that thing should have sounded like it had at least 3 fouled out plugs.

Filter is in the tank and is a lifetime filter. so that shouldn't be an issue. As far as your "Flex fuel Option" there is no such thing. The truck just came out with larger injectors so that it can run E85. Your PCM will have 2 seperate tune settings. 1 for when It detects E85, and 1 for when it detects Petrol. It's not really something that you just shut off.
I'm sure a tuner can tune around it, but no reason to.

 

This will technically only be true if the engine isn't getting up to 210 degrees. If it is in fact operating at 180 degrees, the PCM could be feeding it more fuel to help it warm up