Theo Tash

So I recently finished building my 2012 Express 3500 cutaway dually 6.0 flex fuel. I found an ad listing a FREE Chevy Express van so I talked myself into checking it out even though it was over 2 hours away and I was ready for bed, But sure enough when I arrived there was the van with the keys in it just like the add stated. It was at a transmission shop that had the vehicle for over a year never got paid for the work so he removed the transmission and kept it the following parts were all missing: the transmission, two catalytic converters, two upstream oxygen sensors, one downstream oxygen sensor the transmission crossmember, the drive shaft, I replaced the transmission with a GM factory rebuilt unit with less than 5,000 miles on it, the catalytic converters and oxygen sensors were replaced with the least expensive parts that I could find on RockAuto. And the drive shaft from a salvage yard halfway across the country. I removed the box Truck body, purchased and installed an aluminum/fiberglass utility body. It was plenty of hard work but I feel very fortunate to have been able to complete it and I now have this awesome truck to show! I'm very excited to put it to good use so please believe me when I say any feedback is thoroughly appreciated. The one thing that needs resolution is the fuel economy. Running regular 87 octane gasoline with mixed driving the economy is under 5 miles per gallon. I found a 3 pin connector in the harness underneath the driver side of the vehicle which has nothing plugged into it. The connector matches online images of the flex fuel sensor. If the previous owner removed the flex fuel sensor the fuel lines would show some kind of visible splice or reconfiguration, I don't see one that is readily apparent but during the build as I was reattaching fuel lines the routing and connections did seem a little jumbled. I'm certain I put everything back the way that I received it. Since I've had it I've never connected a fuel filler neck and gas cap pluss left a return line disconnected at the fuel pump. There's no fuel escaping from the end of the line while the truck is running not sure if it's a a fuel return or for vapors. But I did reconnect it and ran the truck a couple days but still I show no check engine light or pending code for an EVAP leak even with no gas cap.

Perhaps buying a new flex fuel sensor, figuring out where it's supposed to be installed and rechecking the fuel economy after running it for a while is probably the easiest thing to do,
After contacting the local GM dealers and all of the local Parts suppliers and checking online this sensor is out of stock and unavailable. I understand it's part number to be 13577394. Regardless the parts availability there's the opportunity to learn what's actually going on here. Also the nearest E85 pump is 20 mi away from me and I would use 4 gallons of gas to reach it with my current fuel economy). I'd like to explore the possibility of eliminating the flex fuel related components, systems and or its associated programming.

Questions:


​​​​​​With the flex fuel sensor missing or disconnected what does the PCM see?

With no signal data on fuel composition (Ie. alcohol / gasoline proportions) being received by the PCM to what settings will the PCM default the fuel injection and timing? Will it use the gas settings or the e85 settings or is there third "limp" mode?

​​​​​​There are no e85 pumps in my area so I'll probably never use the flex fuel capabilities. The flex fuel injectors as I understand are larger, have four orifices instead of two and have the ability to flow greater volume of fuel. So one thought is that the injectors are flowing the regular gasoline that's in the tank in quantities meant for e85. is there a replacement fuel injector that will physically fit and connect and that has the two orifices/the lower flow rate of the injectors used in non flex fuel/gasoline only engines? (Maybe there's a way to fool it into getting better gas mileage)

Back in the engine bay, under the dog house, the evap purge solenoid sits on top of the engine mounted on the fuel rail.
There's a hard plastic line connecting to the solenoid. This connector is essentially a T fitting, it had nothing on it when I received the truck. I capped the open port in the fitting. Is there another line that should be connected here?

mountainmanjoe

First I would run VIN to make sure it actually is a FF engine.
FYI, my 2013 is a FF model, and there is no alcohol sensor. The computer monitors the fuel trims for a while, and somehow calculates the fuel alcohol content from that data ... or it attempts to anyway. It's actually a very terrible system that gives me never-ending grief (there are bulletins and videos about it online). In my research, even FF owners who did have physical alcohol sensors , were not happy with them
My advice ... disable FF altogether. But you have to have it programmed out of the PCM before you can put normal injectors in there.


FF vehicles are supposed to run on any blend up to E85. That means E5, E10, E15 ... whatever. They're supposed to run on straight gasoline just fine.





it could be on the evap canister