E85 Economy questions
 

Running E85 (OFT Tune) on stock car.

Have been using the in dash readout to measure economy on petrol vs E85

I realise it may not be totally accurate but its a consistent measure so should be good for comparision.


Have noticed it says I am getting same economy on E85 as I was on petrol .

This seems strange as I thought Ethanol had less energy per litre than petrol, so was expecting 15 % or so more fuel use on E85

I would assume that the in dash readout derives its figures from measuring distance travelled vs volume of fuel calculated from injector opening times and injector flow rate.(or their is a flow sensor) ?

So would E85 fuel flow at a different rate through injectors than straight petrol ?? or somehow be causing the flow sensor to read incorrectly.

Or am I actually getting similar economy to petrol

Economy was measured on several trips to work on same route early morning just cruising. It does seem to use more during more spirited driving but hard be consistent with spirited driving.

When that 'E' light turns on,

How many miles did you drive on a tank of E85?

How many miles did you drive on a tank of 91,94,whatever you use?

For me, I would fill up between 250-300 miles on 91 octane (in California)
and on E85, I fill up between 150-200 miles. Of course, I drive it a lot harder on E85 because the pick up is more immediate and it is hard not to drive it more aggressively.

Depending on the ethanol content that may be true. Big the ethanol content is low that means there is more petrol in your ethanol giving it better gas mileage. The e85 stations are about 79%ethanol where I fill up and the gas mileage has gin down from 26 mpg to 17-21mpg depending on how you drive.

i think it has to do with how OFT uses an injector scaler hack to compensate for E85 fuel density. if the actual requested volume isn't increased, but rather 'tricked' into dumping a lot more fuel than it thinks it is through the scaler adjustment, then the calculation the ecu is using to calculate fuel mileage wouldn't be effected.

am i totally off-base here? it seems reasonable to me... as i noticed the same thing when i was using a scaler hack on BRZEdit.

James nailed it. You can't trust the in dash display if you are running a tune. Manually calculate it.

I wouldn't call it a hack, since injector scaling is an integral part of all stock roms. All you are really doing is adjusting the scaler value. I assume the readout if off because the math for the readout is based on the stock values. Not sure if that is pulse width, opentime, etc..

well hack isn't to be taken as a derogatory term... it's just the definition of making a system do something it didn't intend to do. or pretty much exactly what this is :).

the 'non-hack' would be to change what it is intending to do... i.e. increasing requested fuel volume.

but yeah... semantics.

Thanks guys,

Sounds very plausable that the E85 tune is upsetting the maths the ecu uses to calculate dash display readout.

Think thats satisfied me :thumbup:

Well... if everything is calculated correctly it should work just fine :P Messing with tables and letting the ecu think it is injecting .5ml when it is injecting 0.7ml will throw it off. The ecu uses injected volume for calculation as far as I know vs some vehicles that use intake g/s vs afr.

If you have a flex fuel car that is calculating within a reasonable error margin of fuel injection % increase then it should be pretty close to correct. My car on flex fuel seemed pretty close to correct when comparing to my gas station math.

OFT uses injector scaling to skew this so its likely to be quite a bit off. I think a lot of early ecutek based tunes had this as well, as well as after market injectors until people started figuring out what tables actually had to be modified for the ecu to be aware of fuel changes & hardware changes.

exactly... your ecutek tune use an injected volume compensation to adjust for fuel density. if you don't tell the computer you want more fuel.. it doesn't know it's consuming more fuel and the mpg calc is off. just telling it 'you have 160cc injectors' doesn't change the requested fuel volume, it only causes the ecu to overshoot it by 30%.

in other words, it'll never work fine unless the ecu knows how much fuel it's asking for, which with an injector hack it does not.

Im on an ecutek e85 tune and my readout is different from 93 vs E85. On 93 i avg around 26-30 mpg on the dash readout and on e85 i avg around 20-23 mpg on the readout. So far on e85 I avg anywhere between 20-23. If im on E and fill up i get around 260-280 miles and i usually fill up around 11.4-11.6 gallons. in the winter my e85 mpg is usually around the lower side

Multiply the on-dash readout by .72 and that's actually about what you are getting. It reads incorrectly for e85 tunes, at least the current OTS ones available from Vishnu.

Figure between 25% and 30% MPG drop.

this is what i experieced too. also if u are using torque to monitor mpg and other readings the mpg will also have to be scaled.

Using EcuTek you can control actual fuel delivery globally with custom maps. So I can multiply the fuel quantity without changing the airflow nor fueling scalars. So the display is accurate and load calculations are correct. The other platforms rely on changing the injector variable, which is not consistent due to the DI/PI combination. Changing airflows will be global, but it will throw off the load calculations and the meter.