VE table changes for changing B3601 from 14.12 to 14.68

[Gregs]

I want to change from running E10 to running no ethanol fuel. Be it right or wrong I have B3601 set at 14.12 and I want to change it to 14.68...I know the whole E10 argument and don't want to get into that right now. My head is thinking in these two directions right now and I was wondering if I could get some advise.

My first line of thought is that I'm going to need to change my VE table by some scalar because I'm changing my fuel by a certain percentage.

My second line of thought is that the VE table should not have to be changed because it is a theoretical table of the engine's ability to flow air and that the engine will flow the same amount of air regardless of whatever fuel I'm running.

could someone step in and try to straighten me out?

[WeathermanShawn]

Great question.

I still don't get it either and why it is important to change B3601 from the Manufacturers Spec.

Seems if you tuned closed-loop, stoich will be determined by your overall STFT and/or LTFT distribution. My confusion is how is the laymen going to know what stoich is for a particular blend of gasoline.

My hunch is changing B3601 will require some form of re-tuning of the VE Table (depending on how you originally tuned it).

But, I do not know either. We will see what the engineers/advanced tuners can share with us..

[joecar]

When you tuned your VE table:
- what fuel were you using...?
- what stoich AFR was your wideband based on (or were you using lambda/eqr)...?
- what was B3601...?

Generally the VE table stays the same (the fuel's stoich AFR does not change the engine's cylinder VE/airmass ) and the changes are in B3601 and B3605.

[joecar]

Hi Shawn,



I still don't get it either and why it is important to change B3601 from the Manufacturers Spec.
This affects the fuel mass final calculation just before trims are applied.


Seems as if you tuned closed-loop, stoich will be determined by your overall STFT and/or LTFT distribution. My confusion is how is the laymen going to know what stoich is for a particular blend of gasoline.There are published tables: E00=14.6-14.7, E10=14.1-14.2.

When running different fuel, several things must be done:
- B3601 set to fuel's stoich;
- B3605 may need minor tweaking for WOT, this is easier to do in EQR units (EQR is 1/Lambda);
- Wideband must report either lambda or AFR corrected for fuel's stoich (i.e. calc pid to multiply by 14.2/14.7).

Lambda and eqr are regardless of fuel, and suitable WOT lambda or eqr is very close for most fuels.

AFR and lambda are related like this: AFR = lambda * stoich_AFR

This is why it becomes important to work in eqr and/or lambda instead of AFR (use AFR only to aid mental units conversion, not for VE/MAF correction).

[Gregs]

When you tuned your VE table:
- what fuel were you using...?
- what stoich AFR was your wideband based on (or were you using lambda/eqr)...?
- what was B3601...?

Generally the VE table stays the same (the fuel's stoich AFR does not change the engine's cylinder VE/airmass ) and the changes are in B3601 and B3605.


-I was using 93 octane E10 fuel for tuning
-I have my lc-1 set up for lambda
-B3601 was 14.124139

[Chevy366]

There is more to Flex Fuel than B3601 , there are some 14 tables that are used to compensate for Ethanol Content .

[Chevy366]

Do a run and see if the VE BEN factor MAP is still within the 1.00 (+.- 2) , if not re-MAP .

[joecar]

-I was using 93 octane E10 fuel for tuning
-I have my lc-1 set up for lambda
-B3601 was 14.124139Ok, you had corrected your VE independently of fuel type (since you used lambda and set B3601 appropriately).

In this case, when you switch to E00 you should be able to set B3601 to 14.63-14.68 and your VE is good as-is.

[Gregs]

Ok, you had corrected your VE independently of fuel type (since you used lambda and set B3601 appropriately).

In this case, when you switch to E00 you should be able to set B3601 to 14.63-14.68 and your VE is good as-is.

that makes sense. i'll report back.

[gmh308]

Your second line of thought is pretty accurate. The VE of the engine wont change because the fuel is different. As long as you set/log your VE with the same fuel it should be accurate.

The trims will look after the changes from E0 to E10 and back. Typically the LTFT trims in current GM cars/trucks can handle 20 - 25% change in fuel flow. STFT's can handle same or more but if they push the LTFT's to the calibrated limit they will pop a lean or rich DTC. In a late model the trims general adjust after a fuel fill within 2 - 3 miles.

Running E85 or E100 does have an influence on VE relative to E0 but it is arguably a trival effect. 50% increase in fuel flow at E85 does displace "some" air. Splitting hairs to worry about it. On a top fuel engine the liquid does need to be taken into account as there is not much room left for air :).

[Gregs]

well here's my update. I filled up with the 93 non ethanol and i left my e10 tune and i was having ltfts around -8. I put the E0 tune in and ltfts went to around -2. they are still moving around a bit i'm waiting for them to settle down right now, but it seems like everything is fine.

[joecar]

Thanks for the update. :)