Flex Fuel Sensor Not Accurate

[SiriusC1024]

OP recognizes the problem. I've offered two solutions. Getting the part I listed from the source I listed is what I'd do. You guys do what you want.

[TAPyvehc93]

Without seeing the tune and corresponding data log/s it's just throwing crap against the wall to see what sticks.

That being said, unless the tune was dialed in properly, 93 first and completely, then E85, you can't expect the trims to work 100% on point. They ARE fuel TRIMS after all and they're designed to take up the fudge factor. Your trims being off -10% ain't nothing to be sweatin. OE calibrations are lucky to be that close.

Really? I thought it didn't matter what kind of fuel you used when tuning the VVE and MAF as long as you had a actual ethanol sensor installed and enabled in the tune. I did however top off with 10 more gallons of pump 93 today and my content went from 17% down to 12% so I'm starting to think you are correct. The sensor is probably correct, and I just need to retune it with 93 and see how that works. It seems like the lower the ethanol content gets from 68% (which I tuned it with) the more my fuel trims go negative. I'm sitting around -15% now. I just don't understand why it would matter though? If I tune it on 93 wont my fuel trims be off just as much but in the opposite direction when adding e85? I know what you're saying about fuel trims being there for a reason and don't sweat it but they are off just as much when getting into PE. Its wasn't just a part throttle thing.

[edcmat-l1]

E85 is your FLEX fuel. Meaning, it (the calibration) is based primarily on petrol. You need to dial it in completely on petrol, then add your E and adjust E related tables and settings ONLY.

[hjtrbo]

Flex fuel is a good way to weed out injector data. For example, if you're dialled on 93, then fill up on E85 and stoich settings are correct, it should just work +/-5% or there abouts. Any thing significantly more than that you probably haven't got correct injector data. That also assumes good fuel pressure and IDC < 90%.

[sgod1100]

Really? I thought it didn't matter what kind of fuel you used when tuning the VVE and MAF as long as you had a actual ethanol sensor installed and enabled in the tune. I did however top off with 10 more gallons of pump 93 today and my content went from 17% down to 12% so I'm starting to think you are correct. The sensor is probably correct, and I just need to retune it with 93 and see how that works. It seems like the lower the ethanol content gets from 68% (which I tuned it with) the more my fuel trims go negative. I'm sitting around -15% now. I just don't understand why it would matter though? If I tune it on 93 wont my fuel trims be off just as much but in the opposite direction when adding e85? I know what you're saying about fuel trims being there for a reason and don't sweat it but they are off just as much when getting into PE. Its wasn't just a part throttle thing.

I had the exact same thing happen with my ctsv. Had my car dialed in on 93. I usually run about 55-60 blend and once I filled up with 93 to store it for the winter my trim went pretty negative (more than -10%). My stoic table is correct and I know my injector data (ID 1050s) is correct. I'm in the same boat as you. I'm not sure what table(s) to adjust that are just related to E (stoic table maybe?), but I would think that table needs to be left alone.

[hjtrbo]

Give your a blend table a bit of a tickle and see how it goes. If you're forever chasing your tail with different blends then it's an indicator that injector settings should be revisited.

[sgod1100]

Give your a blend table a bit of a tickle and see how it goes. If you're forever chasing your tail with different blends then it's an indicator that injector settings should be revisited.

Is that table something pretty regular to tweak while running an e blend?

[edcmat-l1]

Is that table something pretty regular to tweak while running an e blend?

Yes. Once your base calibration is done, this is where you should bring your trims back in line on E if they're off. And you use your alcohol PE to adjust your WOT A/F on E. The idea is you don't want to touch your base calibration once it's done.

[sgod1100]

Yes. Once your base calibration is done, this is where you should bring your trims back in line on E if they're off. And you use your alcohol PE to adjust your WOT A/F on E. The idea is you don't want to touch your base calibration once it's done.

good deal, thanks for the info. So, in a perfect world would I apply the error that I'm seeing from my trims to the stoic table in the percentage area(s) that I'm running?

[Alvin]

Is that table something pretty regular to tweak while running an e blend?

I've had to do this occasionally.

I always tune first with 93. Thoroughly. My thought is if the stoich table is off I at least want the E0-10% to be as accurate as possible because that is when the car is in most danger for knock.

I've had to go a bit richer than what is technically stoich correct AFR to keep fuel trims and wide open fueling in line on a handful of cars when E content is high.


I've seen some tune shops offer E85 tuning but don't ask you to come in with 93 and fuel cans of E85. The customers are getting short changed IMHO. The car really needs to be thoroughly done on 93 then moved to E85. You need to find proper timing for both.

[edcmat-l1]

I've seen some tune shops offer E85 tuning but don't ask you to come in with 93 and fuel cans of E85. The customers are getting short changed IMHO. The car really needs to be thoroughly done on 93 then moved to E85. You need to find proper timing for both.

Same here. Bring your car with 1/2 tank of 93 and 10-15 gallons of E. Once the 93 tuning is done if there's any fuel left in the tank it gets pumped out so the E content is as high as possible.

[edcmat-l1]

good deal, thanks for the info. So, in a perfect world would I apply the error that I'm seeing from my trims to the stoic table in the percentage area(s) that I'm running?

Yes, kind of. Doing it that way will get your single cell in the stoich table correct but you want the sliding scale correct so the better way to do it is change the 100% cell by XX amount then interpolate across the entire table. Until your target cell is correct. In theory that will correct the entire table.

[SiriusC1024]

Calibrating the sensor and applying adjustments to the AFR table. Like I said. Makes a lot more sense than taking sensor accuracy for granted and saying "those dam tubes always read a little high."

[SiriusC1024]

Changing the 100% cell for a baseline of 93 works, but it could be more accurate. 93 might (probably) contain ethanol already. It's likely closer to E10 than E0, but regardless it'll be in between. Can't be sure.

Now if only there was a way to tell how much ethanol is in our premium gas...
pump e.png

...perhaps some sort of apparatus, device...a technical implement...
tester.png

...hmmmm
thinking hard about it.png

[sgod1100]

Thanks for all of the info guys, I appreciate it.

[edcmat-l1]

Changing the 100% cell for a baseline of 93 works, but it could be more accurate. 93 might (probably) contain ethanol already. It's likely closer to E10 than E0, but regardless it'll be in between. Can't be sure.

Now if only there was a way to tell how much ethanol is in our premium gas...
pump e.png

...perhaps some sort of apparatus, device...a technical implement...
tester.png

...hmmmm
thinking hard about it.png

Yes, and with a working E sensor it's targeting roughly 14.1:1 at 10% Ethanol. What's your point?

[sgod1100]

So, for example if I have my 93 tune dialed in then I add E to around E60 and now my trims are 10% lean. Would I increase the 100% E stoic value number 10% to match the leaner value i'm getting (perfect world of course)? Or am I an idiot and have that backwards?

[blindsquirrel]

I think you'd increase the 100% cell by however much it takes to put the 60% cell at the right spot, when the table is interpolated. If I'm understanding what's been said earlier.

[SiriusC1024]

You would run 93 and measure the ethanol content with the tester. That percentage would be your baseline along the AFR axis accounting for what the sensor reads, and the stoichiometric ratio matched to the math.

So if you're testing 5% E, but the sensor indicates 10% E, then you'd put the stoichiometric ratio for 5% in the 10% column. That's the new baseline.

From there proceed like edcmat-l1 mentioned, but also test your "full e85" mix at the end.

[SiriusC1024]

Yes, and with a working E sensor it's targeting roughly 14.1:1 at 10% Ethanol. What's your point?

My point it to verify the sensor. I agree with your method.