OBD2 Scanner for...

[Nordic]

I have an'08 GM vehicle - Flex Fuel. No doubt many of you have had this situation where the computer keeps upping the Alcohol % to where you get more difficult starting and more fuel consumption in general. I've had the local shop reset the fuel trim more than once but I would like to do it myself to save the cost over time. I ordered one scanner with hopes of compatibility to do this but not so. Obviously the very expensive scanners do it no problem. I'm looking for a recommendation on a lower cost unit that will effectively do the Alcohol % reset. Which one worked for you?

 

[scootergmc]

I've heard good things about the Topdon Topscan module (for the cost). I think it may do fuel composition resets for GM, but don't hold me to that.

 

[Sprint 6]

How about fixing what is actually wrong instead of just resetting? That system really isn't that difficult.

 

[JoeRappa]

The most common thing that causes the flex fuel to read higher than normal alcohol content is doing short fillups. What I mean is that if you fill the vehicle up before it is below a half tank or so it can make the alcohol content drift high more often. If it's doing it often enough that you want to buy a scanner, I bet that's what is going on. If not, there's probably something wrong with the truck.
So you know, I only see this problem on 2 types of vehicles. Ones owned by older folks that keep their tanks full and fleet vehicles, like cop cars that fill up at the end of every shift.
Joe

 

[UncleTom]

How about fixing what is actually wrong instead of just resetting? That system really isn't that difficult.

My sons truck did this and a guy changed the alcahol content. What usually goes wrong that makes them change?

 

[Sprint 6]

My sons truck did this and a guy changed the alcahol content. What usually goes wrong that makes them change?

As mentioned above, short fills and short drives are #1. The virtual alcohol content algorithm needs a minimum of 5 gallons during a fueling event, then it needs at least a 7 mile drive after. Inaccurate fuel gauges come into play.

After the above issues are addressed, then it comes down to intake air leaks or mis-read intake air. If the fueling conditions are met, on the 7 mile drive, the computer watches what the fuel trims do after the fuel fill. If the trims start to trend positive (adding fuel), the algorithm switches to the E85 table and sees if a point on that table starts stabilizing the trend. The point where the trims normalize (+/- 5% ish) the computer converts the map used into an alcohol percentage, stores that figure, and uses it to base fuel mapping until the next refuel event. If no map will correct the trims, then the ECM aborts the test and sets fuel trim codes.

So, it takes an understanding of what the system is doing, and why it is doing it. Any air leaks that introduce unmetered air, but not bad enough to set full blown fuel trim codes, will skew the alcohol learn. Intake gaskets leaks, stuck or dirty PCV, cracked air intake boots, etc. Exhaust leaks before O2 sensors can also induce this because leaks also let in outside air that can skew O2 readings. Other things that can cause this are dirty or inaccurate MAF sensors, missing or chewed up air filters, and aftermarket air intakes.

The diagnosis is straight forward. Test the actual alcohol content in the tank, reset the alcohol percentage, and test drive. Immediately after reset, monitor real time fuel trim. If the trims are higher than +5%, but less than +25%, you likely have an air leak or MAF misreading incoming air. For trucks, I come to a dead stop, WOT, at the 1-2 shift, the MAF should peak above 200g/sec. (5.3 V8s). If it is under 200, ypu have a dirty or bad MAF, or an air leak.

 

[cjunrau]

That is what I call to much computer in a car.

 

[GChief]

And they are not going anywhere, learning how they operate is more effective than complaining about it on the interwebs

 

[MarkB_MI]

Is this problem unique to flex-fuel vehicles?

 

[Sprint 6]

Is this problem unique to flex-fuel vehicles?

Yes. If they aren't sold E85 capable, they don't figure alcohol percentage. Non-E85 just continue to correct the trims until they are so far out a code set, but they can run into mpg issues with the same air leaks or MAF issues. All the parts are the same, other than the fuel pump and injectors. E85 uses alcohol resistant fuel pumps and higher lb/hr injectors.

And a lot of late model vehicles directly read alcohol through a sensor in the fuel line. Early ones used a sensor, too, but the mid-2000's gm's used the virtual system due to sensor cost. The sensor cost dropped greatly, so they went back to directly reading fuel content.

 

[560Dennis]

Interesting I have a flex fuel 2011 5.3 gmc

manual says the flex fuel will get less mileage but I never check the fuel economy, think I will. Post the results to compare to .

 

[Sprint 6]

Interesting I have a flex fuel 2011 5.3 gmc

manual says the flex fuel will get less mileage but I never check the fuel economy, think I will. Post the results to compare to .

There is less Btu/gal of ethanol than gasoline, so less mpg. Thing is, though, ethanol Btu and octane is consistent, gasoline Btu varies based on region, season, etc.

Ethanol is actually a better fuel than gasoline. I wish we would revamp our production process, and build dedicated engines for it, like Brazil.

 

[adediesel]

is this a cold wx problem? or does it happen year round? I would try e15. but I not educated in fuel trims and I have had four flex fuel vehicles and never had a starting problem or other issue that I know of.

 

[Hobo,NC]

This chart is nice to have. To quickly check MAF record MAF at WOT at 5000 RPM divide by 40 you should come up very close to engine displacement.

 

[560Dennis]

Saw this kit installed on Sams Garage .

ProFlex DXI: Adaptive Flex Fuel System for Direct Injection

PROFLEX Commander is a bolt on performance flex fuel system allowing your vehicle to make big power with ethanol, such as E85, right out of the box. No tuning needed!

www.advancedfueldynamics.com

 

[Nordic]

I have an'08 GM vehicle - Flex Fuel. No doubt many of you have had this situation where the computer keeps upping the Alcohol % to where you get more difficult starting and more fuel consumption in general. I've had the local shop reset the fuel trim more than once but I would like to do it myself to save the cost over time. I ordered one scanner with hopes of compatibility to do this but not so. Obviously the very expensive scanners do it no problem. I'm looking for a recommendation on a lower cost unit that will effectively do the Alcohol % reset. Which one worked for you?

Thanks for everyone's input and opinion. I will sum this up a bit from my viewpoint. First of all i should say that I have been very pleased with my vehicle especially the first 8-10 years with no hiccups from the fuel trim. The scenario holds very true about driving habits and fuel fill ups. The Alcohol % started going up after retirement. We now live on the edge of a small town, most of our local trips are 5-10 minutes and then time to park. The price of gas is significantly higher in our little town than when we go the big city, therefore I always fill up gas for the advantage of cost saving, even if the tank is only half empty. So, like Sprint 6 suggests, fixing the real problem would be fixing ME and my habits. That said, I'm not going to drive 7 miles each time and fill up with expensive gas to keep the vehicle computer happy!! This is where the Flex-Fuel idea fails. Being that, doing the fuel trim reset is relatively simple, it is a cheap fix to do myself but I just need a reasonably priced OBD2 Scanner that will effectively do the reset, which was the original intent of this topic. We have a very good local auto repair shop and they are the ones that have done the fuel trim reset up to this point. It is now due to be done again, but we all know which direction rates are heading. In addition to lack of smooth cold starts it does use about 10% more fuel when the Alcohol % is too high.

 

[GChief]

they are the ones that have done the fuel trim reset up to this point.

How much do they charge? How often do you have it done?

There is probably a good reason in those answers to maybe raise the "budget" and get a "better" scanner that will do that function and more.

 

[Nordic]

How much do they charge? How often do you have it done?

There is probably a good reason in those answers to maybe raise the "budget" and get a "better" scanner that will do that function and more.

I don't remember what the charge was the last time and I may have had some other work done in addition at the same time as well to make the bill higher. Someone recommended a scanner in the $200 range which would pay itself back fairly quickly, considering some more sophisticated units cost $1000 and up.

 

[Sprint 6]

I still bet you have a MAF problem or PCV vacuum leak causing your issue. I have several customers that short trip these trucks without issue. If you're putting gas in it in another town, you've got the fill procedure down. And the after fill alcohol learn only matters if you're switching between E10 and E85. If you're staying with one or the other, if the learn aborts, it doesn't matter. The fact your alcohol percentage creeps up tells me you are getting it into learn mode, otherwise it wouldn't be an issue. You have a repairable problem.

 

[MarkB_MI]

I'll note that nobody has answered the original question.

I use the ODBLink MX+ scan tool, which works with a separate app called OBDLink on my phone. I also have a subscription to Gretio, which is a third-party app specifically for GM vehicles that works with the MX+. I have no idea if either OBLink or Gretio provide the ability to reset fuel alcohol percentage. I do know that if you clear all the problem codes with OBDLink, it pretty much resets everything in the ECM, which I assume would also reset the fuel content. YMMV.