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Randon Thought: Flex Fuel?

Explicit_Spade

Explicit_Spade

Perma-Banned! JK LOL
If I were to set everything up for E85, but wanted the ability to run gas without having a laptop with me to switch tunes could this be done?

What if the high octane settings were for the 85% ethanol and the low octane settings were for 91+ octane gasoline.
 


Explicit_Spade said:
What if the high octane settings were for the 85% ethanol and the low octane settings were for 91+ octane gasoline.
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I would love to know this as well, cause I would consider it. I have "heard" that our 3800 tunes only use the high-octane table, and that they do not sense octane content. Not sure if that is true though. Would need some more experienced folks to chime in on that.
 
That's how the flex fuel cars it. I'm sure there's more to why the pcm switches to the low octane table, more knock of something..
 
They go to a low octane table when knock is present and in a way mixes both tables together to pick a timing number to use. Otherwise without knock it uses the high octane table.

3800 computers do not sense alcohol content in fuel, they are too stupid to do that. Flex fuel vehicles either have a virtual FF sensor that uses the o2 sensors to sense a change in oxygen in the gases, then it guesstimates a alcohol content to use. Then the computer has 2 other timing tables along with adders and multiplers for alcohol content. It's far more complex that anything these cars could handle. The other way is a real flex fuel sensor to measure alcohol content, that too uses the same tables but is far more accurate.

If you owned an early LS1 car there is a company that installs a 2nd "memory stick" in the computer that will allow for 2 seperate tunes on the same computer. You just have to flip a switch to swap between the two.
 
This is all theory, but... on an e-85 tune, wouldn't 91 octane/ E10 fuel cause knock and would force the PCM to revert to the low octane table?

Stoich for 91 Octane/E10 would be (14.7 x 0.90) + (9.00 x 0.10) = 14.13 AFR.
Stoich for E85 would be (14.7 x 0.15) + (9.00 x 0.85) = 9.855 AFR.
Stoich for winter/blend E70 would be (14.7 x 0.30) + (9.00 x 0.70) = 9.310 AFR

With that being said, if you set the AFR for E85, once the gasoline is noticed as causing KR by the PCM (which will happen due to the lower octane) and it reverts to the gasoline/low octane tune, the car would just run rich.

Who has a stock donor car locally that I can try this on? lol
 


I cant remember what thread I read this on but arnt we able to run a mix blend of E85 w pump gas around 30% for E30 without creating any adverse effects? Are there any advantages to running this mixed blend or Is one just wasting time doing so?.....
 
Wouldn't you need to also change the fuel tables? Not sure how you could accomplish that without flashing every time you switched fuel.
 
I'm running a 40% 91/E85 blend now. it is a bit of a fuss to calculate the ratios and use a gas can at the pump. All I have done is tune the mass air flow sensor because ethanol makes the car run leaner. I am planning on switching to pump E85 in the next couple weeks. the problem I run into is that the gas station that sells E85 is 90 miles away, so I will be using gas cans to keep the car filled up. I don't drive the Grand Prix everyday, so it should be fine.

to the original poster: it is a simple thing to have multiple tunes saved with hp tuner, and switching back and forth would only be a matter of draining the gas tank, filling up with the desired fuel, and then loading the associated tune.
 
Or have a spare pcm with the e85 tune and you can just swap pcms. You would have to wait for the shifts and fuel trims to learn again tho.
 
Just carry an extra pcm in the trunk set for the alternate fuel and when you fill up, swap the PCM's...

done...
 


This could possibly work, but not that great. The change doesn't happen immediately.

But, the problem is, your fuel trims won't be able to change fueling enough.

Also, running e85 (unless you aren't really using it) and then going to 91, will be pretty hard on the motor with all the knock it will see.
 
Explicit_Spade said:
This is all theory, but... on an e-85 tune, wouldn't 91 octane/ E10 fuel cause knock and would force the PCM to revert to the low octane table?

Stoich for 91 Octane/E10 would be (14.7 x 0.90) + (9.00 x 0.10) = 14.13 AFR.
Stoich for E85 would be (14.7 x 0.15) + (9.00 x 0.85) = 9.855 AFR.
Stoich for winter/blend E70 would be (14.7 x 0.30) + (9.00 x 0.70) = 9.310 AFR

With that being said, if you set the AFR for E85, once the gasoline is noticed as causing KR by the PCM (which will happen due to the lower octane) and it reverts to the gasoline/low octane tune, the car would just run rich.

Who has a stock donor car locally that I can try this on? lol
Click to expand...

You can't just go putting in different Stoich settings into the PCM. It will always run Stoich no matter what as the O2 sensor only reads Stoich. So when the car is running correctly on E85 it's running at 9.8:1. All I needed to do in order to run E85 on my 05' was change the IFR table by 34%. I have my wideband set to read on a gas scale because when talking to people they don't really know rich/lean on a E85 scale so it's just easier to state you are 12:1 or 15:1 than it is to say you are at 6:1 or 10:1. Just seems more people understand gas over E85.
 
J57ltr said:
You can't just go putting in different Stoich settings into the PCM. It will always run Stoich no matter what as the O2 sensor only reads Stoich. So when the car is running correctly on E85 it's running at 9.8:1. All I needed to do in order to run E85 on my 05' was change the IFR table by 34%. I have my wideband set to read on a gas scale because when talking to people they don't really know rich/lean on a E85 scale so it's just easier to state you are 12:1 or 15:1 than it is to say you are at 6:1 or 10:1. Just seems more people understand gas over E85.
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no its whatever you set stoic in the pcm is hat it will command. raping ifr is completely unnecessary if the right Stoich Is input.
 
The O2 can't read anything other than Stoich anything on the rich or lean side is just a guess this is why we run a wideband. I guess I could see that if you punch it in as a different amount, but it didn't seem to work on my 05'. Then again skew doesn't work either.
 
It may command whatever stoich is, but that's not necessarily what it will run. For instance, you can change stoich to 17.0 on a stock car, but the trims will correct it to actually run at 14.7.
 


GTPpower said:
It may command whatever stoich is, but that's not necessarily what it will run. For instance, you can change stoich to 17.0 on a stock car, but the trims will correct it to actually run at 14.7.
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trims will correct to whatever stoich is set too.
 
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