poormxdad

Gentlemen,

I have been running 14.7 as StiochiometricAFR in the General Setting Tab for Tuner Studio since I had no problems getting 93 octane without ethanol. A large portion of my AFR Table below 100 kPa is also set to 14.7. I'm using "Incorporate AFR Target" for calculating fuel. Unfortunately, these days, it's harder to find non-ethanol gas, even at the track. I know that although gasohol can contain up to 10% ethanol, it's usually lower than that.

What is the current recommendation for stoich for a track car assuming limited availability of clean 93?

Thanks,

afm

iTrader: (3)

I do not have an answer for “by how much should I change my fueling.”

That being said, whatever the answer is, it is not typical to change your target AFRs to account for this difference. The typical way to correct fueling would be by scaling req_fuel alone.

O2 sensors measure lambda, not AFR. So a car running e85 with a standard AFR gauge will still read 14.7 at stoich. You can change the gauge face or display to match, but most people find that confusing.

As a result, most people just live in the “take 14.7:1 to mean lambda=1” world and would only scale up req_fuel to account for small fuel composition differences.

poormxdad

Thanks. Do you have a recommendation for what I should use as stoich when running available E10?

patsmx5

iTrader: (16)

If that number is off by say, 2%, it won't matter in the long run as that's just the starting point in the calculation.

Once closed loop fueling is running, it uses the O2 sensor feedback to judge if it's rich or lean of target AFR and will remove/add fuel as required to hit target. So either way, you end up at target.

You could type in a stoich ratio of 13 instead of 14.7 and eventually the car will drive the same as if you typed in 14.7, just there will be more error in your initial fuel calcs until the closed loop tuning brings that error to zero.

patsmx5

iTrader: (16)

If you want an exact number, I believe 6% is a common ethanol value, so lookup stoich for 6% and use that as your starting point.

poormxdad

Alrighty then... let me ask it a different way.

Forget the stoich number in General Settings. For discussion purposes, let's say I can only get E10, and it's truly 10% ethanol. Stoich for E10 is ~14.1. If I had previously set up my AFR Table for ethanol-free fuel, wouldn't I want to update the table now for E10? Here's my table.



I'm concerned that much of my table is 4% too lean given the ethanol, and perhaps I should make changes throughout.

The car is tagged, but HPDE-only.

Thanks,

Ted75zcar

iTrader: (2)

no, that table should not be changed if you are using 14.7 as the stoich value in "General". As mentioned previously, the MS doesn't work in AFR, it works in Lambda and then translates it to AFR cause it is easier for people to understand. What you need to adjust is reqFuel (the calculation utilizes a separate instance of a stoich value IIRC).

poormxdad

Ted,

I believe the answer is Yes--I need to update the table AND the StoichiometricAFR value in the General Settings tab. My issue is that all the research I've done says "up to 10% ethanol". Sunoco's website even says "up to 10%". I wanted to know what other folks who were running 93 octane gasohol on track were using for a stoich number.

After a couple of beers, it seems like setting the tune up for some amount of ethanol but running ethanol-free gas when able, is better than the reverse. Pat's suggestion of 6% seems reasonable. For 6%, I calculate stoich at 14.358 or ~14.4. Then the question for me becomes, do I reduce my entire AFR table by 0.3, or is it rich enough up top the way it is?

DNMakinson

iTrader: (3)

Just log your EGO for a while and if it is running, say, 103% on average, due to the addition of the methanol, then multiply your entire VE table by 1.03 and call it a day.

Or, as mentioned above, adjust your Req’d Fuel by 1.03 and pick up alll your cranking, etc values as well.

Basically, you have a situation where your injectors just got slightly smaller, so that could be the best approach

DNM

Ted75zcar

iTrader: (2)

side note, I think Phil must have made some changes to TS, as I am almost certain these two locations for stoich weren't linked in older versions. Could be wrong.

Edit: and DNM's suggestion works as well, the table feature in MLV can help visualize the steadystate EGOcorr IMO, and I would still be adjusting the reqfuel by steadtyState_EGOcorr/100

poormxdad

Gents,

I don't understand how that would work. If I add 3% fuel but leave the AFR Table alone, won't EGO just remove the extra fuel if the tune is hitting the AFR Target?

Now for the $64,000 question. Since I'm using Incorporate AFR Target, if I change the stoich value in the General Settings Tab, and I change the values in the AFR Table accordingly, will the MS automatically adjust the fuel to meet the new AFR Target WITHOUT me having to update the VE Table?

Thanks much for taking the time,

Ted75zcar

iTrader: (2)

I think what you are missing is the connection between AFR and the function of the WB sensor. The WB doesn't measure AFR, it measures lambda, and then TunerStudio and the MS calculate an AFR value from lambda. This is only valuable as a human readable/understandable number. If you have a gasoline WB gauge and you change that stoich value in general along with scaling the AFR table, the gauge and the TS value will not match. For gasoline, lambda = 1 is equivalent to AFR 14.7. The MS fuel algorithm (with incorporate) divides the stoich value in general by what is in your target table to produce a lambda modifier value that is then used to scale the delivered fuel in the fueling equation. EGOcorr divides the actual measured value by the target value and that value is also used to scale fuel in the fueling equation.

This cat can be skinned any number of ways. You have been presented with a few in this thread. As I have stated, the clear winner (IMO) in the absence of an ETH content sensor is to use reqFuel, this is the base value that is used for every fuel correction/modifier (with a couple of exceptions). I am flex, but I use a base stoich of 14.7. When I am running 100% gasoline, the 14.7 I see on my gauge and in my logs and on the TS dash is actually probably close to 14.7 lbs/lb. When I am running e85 manna-from-the-gods a reported value of 14.7 on my gauge, logs, and TS dash is actually closer to 10 lbs/lb.

Edit: and as a follow-up, if you change both the general settings tab stoich and scale AFR target, you will not be doing anything to the actual amount of fuel delivered, and in your case, will be lean open - loop. (14.7/14.7) = (14.2/14.2) = 1 = lambda.

poormxdad

poormxdad

I believe I may understand now. From the Help popup on "Stoichiometric AFR" in TunerStudio (emphasis added by me):

"The stoichiometric (chemical ideal) AFR for the fuel in use. This is only used when 'incorporate AFR target' is enabled. For gasoline use 14.7. For alternate fuels, alter this number, alter the AFR target table and set your wideband calibration appropriately."

Nothing I do will change the fact my older MTX-L with Bosch 4.2 sensor is calibrated for 14.7, unless I can recalibrate it using an "LM Programmer", which cost as much or more than a set of track tires.

Is that pretty much correct?

redursidae

Let’s address this again and maybe it’ll help. If you ignore the number in “General”, you’ll leave your AFR tables as is. This is because the table is really Lambda underneath, and Tunerstudio and Megasquirt are converting it to AFR for our brain. If you can only get E10 from now on, you’ll need to add more fuel to hit Stoich, and the best method in MS is to increase req_fuel.

If you put your MX-L in a car with e85 tuned perfectly, the gauge would still show 14.7 at stoich. This is because O2 sensors read lambda, the content of oxygen in the exhaust. Stoichiometric means a complete reaction, and we define that as 1 Lambda and this is true for all fuels. Your gauge just shows that as 14.7 because we humans read that easier. Megasquirt and Tunerstudio do the conversion in the logs and gauges by using the Stoich value in the General tab.

Yes, you will need more fuel when you switch to E10. You can increase your VE table or req_fuel, but req_fuel will also adjust AE, warmup, cranking, etc. hence why the answers above are suggesting you increase it.

What I would do as a starting point is to use the req_fuel wizard, and there use the AFR for your new fuel (E10=14.1). You should see the number increase. Then set your Stoich value under General back to 14.7 for the only reason that you’re used to seeing 14.7 as stoich. As we stated, the value in General is only for unit conversion. The ECU nor your sensor care about this value because they read Lambda. To drive the point home further, if you were using Lambda as your unit of measurement in the AFR table there would be no change, and you would adjust your req_fuel and be done. You can actually change this in project settings and see what we mean.

Verify that you’re hitting your targets after changing req_fuel and adjust further if needed.

DNMakinson

iTrader: (3)

“Verify that you’re hitting your targets after changing req_fuel and adjust further if needed.”

Though it is best to understand, it is not necessary to do so in order to obtain the desired result.

DNM

poormxdad

Then my instructions are to change the stoich number in the Required Fuel Calculator to 14.4 (or whatever) and see what it gives me for Required Fuel. In my case it goes from 3.9 to 4.0. Then, change stoich back to 14.7, but put 4.0 back into the Required Fuel box. Is that correct?

The problem with not understanding--and I still don't--is that I won't know if I'm doing something wrong. I believe I've grasped that my sensor is calibrated for 14.7, but I don't understand why I can't just richen up the AFR table in places I'm concerned about, let EGO do it's magic, take a log,and make adjustments.

Thanks to all of you for putting up with my slowness...

redursidae

Yes, this is the way.

No problem, it is a confusing topic. Just like your gauge is calibrated to 14.7, your AFR table is calibrated/scaled to 14.7 with the Stoich in the General tab. If you change your 14.7 to 14.4 in the AFR table (with 14.7 in the General tab), you're changing from 1 Lambda to 0.98 Lambda and run 2% richer, not stoich. A small but important distinction is that your gauge is calibrated to 14.7, not your sensor. The sensor reads Lambda, which is why this all works.

When tuning it is best to follow the KISS principle, and the least confusing you can make it the better. Leaving 14.7 in General and not touching your AFR table is the least confusing setting.

Trust us in this. You could just add pump gas, make no changes, and watch EGO adjust the small change. It will likely be such a small change that you think it's normal error, and this will happen as you fill up in different pumps throughout the year. To adjust for this change, update your req_fuel as stated above.

Reverant

iTrader: (10)

LM programmer is a free utility from Innovate. You only need a USB-to-serial cable and the cable from Innovate that converts the DB9 serial port to the 3.5mm socket. Maybe $20 in total?

poormxdad

Follow-up post.

I made the change in Required Fuel from 3.9 to 4.0. I've done three track days since. The car runs well. It seems smoother. The only problem I had was a long, cold temperature start. I reduced the fuel in the 100 kPa/700 rpm box in the VE Table and it was much better. I could probably take out a little more.

I've attached my current tune and a log from a 30 minute track session. Any comments would be greatly appreciated.

Thanks much,