2015 E92 ECU not adjusting for Flex Fuel?

[TriPinTaZ]

I'm tuning a cammed 2015 Silverado with a 6.2L. Everything is great and as expected on 93. But as soon as we start adding Ethanol Content the fuel trims start increasing meaning the truck is lean. By the time we get to E70, the trims are maxed out trying to add 30% fuel and the truck sputters because it still isn't getting enough fuel. Adding fuel in the tune on E70 starts correcting the issue.

I've tuned countless Gen V cars for Flex Fuel, all of the tables and configs are correct. But it actually seems like, even though the ECU is reporting the proper ethanol content via VCM scanner, that the truck isn't actually adjusting the volume for the ethanol content.

I remember hearing about early E92 ECU's having issues with enabling flex fuel but I've never run into an issue or looked into it much. I'll probably go do that now. But if anyone has run into a similar issue please share. This truck runs great until we start putting Ethanol in it.

[Ben Charles]

Does stoich change?

[TriPinTaZ]

Nope, it just goes lean until the fuel trims try to bring it back. I tune in Lambda so stoich is always 1.0. By the way this is at part throttle, not WOT, so we aren't running it out of fuel. Everything in the scanner reports like it should except it just goes way lean on E like the ECU thinks its still trying reach stoich on E10 gas. The ECU is reporting the correct Alcohol % and Ethanol Content %(which is what I think the ECU uses to choose the stoich from the stoich table. It adds Flex Fuel timing like it should and everything.

I'm scratching my head here. Basically, the ECU says it knows its on E70 but the fueling is like it is still on pump 93.

[5FDP]

Dumb question, is the stoich table itself in the tune set to change or does it say 14.10 for all cells?

[TriPinTaZ]

Dumb question, is the stoich table itself in the tune set to change or does it say 14.10 for all cells?

I changed it like I do for all Flex Fuel tunes. Take a look at the file if you'd like. I was hired to clean up the tune from a shop that does a bunch of trucks. I wont call them out but they pretty much ghosted this guy after they tuned it and it left the shop. I fixed the stalling and drive-ability. But he did have stumbling issues on high Ethanol content before I got involved. It is just today that I figured out the truck isn't compensating for the ethanol like it should be. Maybe the shop had no idea either and didn't want to deal with it. This shop does a bunch of trucks so seems odd.

Here is a file and a log, not everything is how I would tune it, but I was only fixing issues rather than trying to rebuild it. I did blow away the previous tuners Flex Fuel stuff and tuned it my way. This allowed the owner to run up to E40 without stumbling but I think I just allowed the fuel trims to help as the previous tuner disabled them.

SBTffa.hpt
Silverado cold stumble2 E70.hpl

[TriPinTaZ]

I actually just checked the DTC's and noticed the previous tuner didnt enable the codes for flex fuel sensor circuit low/high. I don't think this has anything to do with it but I'm going to enable them and test.

[GHuggins]

I made some changes - just copy all, do a quick re-tune on the MAF and see what happens. I know your probably going to think all of the changes in this don't make a lick of sense, but for whatever reason on the gen5's I've tuned alcohol on, these "non alcohol" settings have worked good. In fact it usually takes them about an 1/8 mile of driving, but they do at least adjust fueling for the alcohol after that. I would "think" your sensor wiring is right since your seeing the percent change in the scanner, so don't think that's the issue, but weirder things have happened... I made some changes to your fueling, both high pressure and timing not to mention your flex settings - these are all currently working pretty well in other 6.2's.

[TriPinTaZ]

Thanks G. You would think this is going in the opposite direction by disabling Flex Fuel. Is your theory here that these trucks actually need to use the "virtual" logic even though there is a sensor installed into the factory harness? The owner wants to be able to changes fuels on the fly.

PS, I didn't do the install but the sensor is plugged into the factory harness hidden under the truck. Seems to be common for the trucks.

[kevin87turbot]

Wow. That's something to keep in mind on these. I've converted several GEN 5's to Flex Fuel and have never run across this issue on them, but I'll remember this thread if I do.

[GHuggins]

Well, let me know if it fixes yours. Actually that flex tune is using DI fueling in combination with still using the "added" sensor as a "virtual" stand in. It will still adjust for the ethanol content, it just doesn't do it instantly - it takes about 3 or 4 minutes or an 1/8 mile of driving. I've actually ran into this problem more on the newer camaro platforms over anything else. They run pretty good with the DI fuel settings. The above tune has the changes applied to your posted tune.

[TriPinTaZ]

Well, let me know if it fixes yours. Actually that flex tune is using DI fueling in combination with still using the "added" sensor as a "virtual" stand in. It will still adjust for the ethanol content, it just doesn't do it instantly - it takes about 3 or 4 minutes or an 1/8 mile of driving. I've actually ran into this problem more on the newer camaro platforms over anything else. They run pretty good with the DI fuel settings. The above tune has the changes applied to your posted tune.

That is exactly what I was wondering if it would do. I spoke to the owner last night and advised him of the new plan. Since we're not on the dyno anymore I am having him install a wideband in the truck so that we can capture that data as well and ensure it is still safe at WOT. Once he gets this done I will load the file and start adding ethanol. I'll report back with my findings. Either way, I appreciate the help, sir!

[sevinn]

I feel like I missed something here, just setting it to virtual would make the sensor useless would it not?

[TriPinTaZ]

I feel like I missed something here, just setting it to virtual would make the sensor useless would it not?

I think the issue with this early e92 ECU may be that the sensor itself does everything a normal flex fuel tune would need it to do EXCEPT actually adjust the volume of fuel needed. So by leaving the sensor plugged in and reporting to the ECU, you will be able to use the flexible timing logic etc. But by leaving it set to "virtual" you allow the ECU to use the O2 sensors to detect the large change in stoich to adjust for fuel volume. I've heard of the newer Ford ECU's doing this but they use wideband sensors. I suppose the same logic can be applied to narrowband since they are always trying to maintain stoich, but they wont adjust for fueling at WOT like a wideband ECU would. I believe the Ford GT350 ECU works this way and you can run Ethanol without a conversion.

[GHuggins]

Well, I think the OE is getting a little trickier trying to make things harder on folks like ourselves to be honest. Don't know how many on here tune multiple platforms, but I've personally been noticing the OE REALLY "construing" tables and then using multipliers or other means elsewhere in the tune to "normalize" things out. Mopar is probably the most noticeable for this especially on their 10 to 12ish yr models - just look at one of their VE tables and tell me how that looks right or even GM on the genV's where they have HUGE fuel pulls or cuts right around where the MAF typically prioritizes yet they'll still run right with the MAF dead, so explain that one - must be something else contributing right?

Same goes for the E85 tables setup from factory on these gen 5's - they leave stoichio set to 14.1 even though they're designed from factory to be a flex fuel vehicle, so where are they making the adjustments for fueling? Must be in the DI or like tables right? Well, that's how I looked at it anyway and started digging from there.You do have to set it to use the sensor instead of virtual per say, but leave the "typically changed" key components alone...

[Camaro6]

Although I don't care for the supplied tune which OP already mentioned, I changed it some for OP. I've had early E92 not work correctly on flex fuel if all the o2 sensors are unchecked, didn't matter if they are "no report." Crazy to me, but could be because the oem virtual uses fuel trims to figure itself out. Figured I would change it to what normally works for me, and he can give it a try. Also, "write entire" when loading it as I've had that happen once or twice on early ones and doing that cleared it up.

[TriPinTaZ]

Although I don't care for the supplied tune which OP already mentioned, I changed it some for OP. I've had early E92 not work correctly on flex fuel if all the o2 sensors are unchecked, didn't matter if they are "no report." Crazy to me, but could be because the oem virtual uses fuel trims to figure itself out. Figured I would change it to what normally works for me, and he can give it a try. Also, "write entire" when loading it as I've had that happen once or twice on early ones and doing that cleared it up.

You know, being this truck was tuned by an alleged reputable shop, I never stopped to look at the DTC's for the O2 sensors. The previous tuner turned off LTFT's and disabled all O2's, I noticed the LTFT's but never the DTCs. I'm still waiting on the owner, but I'll report back with my findings on all of the suggestions here. I appreciate the assistance from all of you.

[sevinn]

You know, being this truck was tuned by an alleged reputable shop, I never stopped to look at the DTC's for the O2 sensors. The previous tuner turned off LTFT's and disabled all O2's, I noticed the LTFT's but never the DTCs. I'm still waiting on the owner, but I'll report back with my findings on all of the suggestions here. I appreciate the assistance from all of you.

That's probably going to do it.

[GHuggins]

Hmmm. I've personally never had a problem with disabling rear O2's for deletes on these, BUT I've never killed LTFT's - don't see why you would want to really... Everything's always worked for me unless the E85 settings just "allow" me to work around the O2 issue?

[TriPinTaZ]

Hmmm. I've personally never had a problem with disabling rear O2's for deletes on these, BUT I've never killed LTFT's - don't see why you would want to really... Everything's always worked for me unless the E85 settings just "allow" me to work around the O2 issue?

I haven't had a chance to test your stuff yet. I'm making the owner install a wideband for safety. The previous tuner disabled the Primary O2's as well. I always disable the rear and never have had an issue there either.

[Camaro6]

I haven't had a chance to test your stuff yet. I'm making the owner install a wideband for safety. The previous tuner disabled the Primary O2's as well. I always disable the rear and never have had an issue there either.

Front O2's I'm pretty sure need to be working for flex fuel to be active since I don't recall the vehicles changing much on E content until up to temp when I'm on the dyno and put E90 in them. Some Gen V I have to plug in the rear 02's to eliminate codes even if it's set for no report after a forced update on the HpT OBD2 device. Rear O2's can be out of the exhaust and tied up out of the way, but plugged in to complete the circuit.

Here in IL I have to check DTC "SES" otherwise the car will not report "completed" on the self tests for emission purposes. I've noticed some vehicles will not heat the o2's if the heater DTC "SES" isn't checked also. They warm up much faster with it checked. That's my .02 and hope it works for you with GH or my changes.