Ethanol Content Sensor for Straight E85?

[CLEM0]

Hey all,

 

Is an ethanol content sensor required for an E85 only tune?

I was under the impression it was due to the variable nature of pump E85- which can vary wildy in ethanol content.

I guess my question is- can a tuner compensate for this with a flex fuel sensor or is it not required for straight E85?
 

I just bought one but i'm unsure if I should just return it.

Cheers all!

[GTSBoy]

It's not strictly necessary, because, whilst the wildly "variable nature of pump E85" is a thing, it doesn't really vary so much that it has to be a problem. It can often be as low as 70, from what I understand, and even somewhat higher than 85. But here's the thing. The knock resistance from ethanol content pretty much reaches a maximum somewhere around 45% ethanol content. Thereafter the extra ethanol doesn't really provide much more ability to put in timing, safety from knock, etc. What it does do though is affect the required stoichiometry. For lower E content, you get richer (for a fuel system/table that assumes E85). So you get safer. And slower. Above 85%, unless the tune is pretty close to the edge of being too lean, you should still be fine. So if you want to keep your tune nicely optimised against varying E content, then....you need a sensor.

If it were me, I'd put a sensor in. The downside here is that you must do the full flex tune to get the benefit from it. You have to have a base map on one fuel and another on the opposite extreme of the E content to interpolate against. I wouldn't think that tuning on exactly E85 (or whatever happened to be coming out of the pump that day) would give the ECU anywhere to adjust to based on what the ethanol sensor is saying, unless there's that other fuel's tune in there also.

[Duncan]

I think it depends on whether you are using pump or can e85, the stuff direct from the refinery is pretty strict e85 I understand while the pump stuff varies from season to season to give you a chance starting the car on a cold morning.

I'd 100% put it in if I was even considering some ethanol.

[joshuaho96]

Personally even if I planned on running straight E85 all the time with no variability to account for cold start I would run a flex fuel sensor purely because any time you switch between pump gas and E85 you'd have to either fully drain the tank. I want to be able to switch to pump gas halfway, end up with E30 or whatever it ends up being and just keep driving without having to deal with AFR trims being all over the place.

[Murray_Calavera]

If you were 100% sure that you will never ever run anything other then pump e85, then sure you could get away without running a flex sensor. 

Lets say the car was tuned on a tank of e80 and everything was setup perfectly on that %blend, as you drove the car and the ethanol content varied from e70 to e85 depending on what the fuel bowser was filled with at the time, you would not notice any change in how the car behaves. It would make the same power and drive exactly the same regardless of if it was currently at e70 or e85 or anything in-between. 

The only way you would notice anything is if you had a dash/gauge telling you that something was different, e.g. AFR is  currently 11.3 however when tuned it was 11.5 under the same circumstances. These small changes will be impossible to feel in the way the car actually performs.

So, should you use the flex sensor? I'd say yes, even if it was just to give you the option to use pump 98. There might be a situation in the future you haven't accounted for where you run out of e85 or it's not available for whatever reason, now at least you can still run the car happily on 98. 

[admS15]

Can you run without it, yes.

Should you, probably not.

My car runs 1 as it's flex tuned. I run e85 all the time, may run 98 once a year just to purge the system out.

In Victoria, the ethanol content from United pump e85 seems very consistent, my sensor reads it as 78-79%, have seen 80-81% a couple of times. I haven't verified how accurate my sensor is but wouldn't be too far off. This is over 5 years, never been under or over those figures.

On another note, you could get one of those portable ethanol test kits but you would need to take a sample each time. 

Since you already have the sensor, why not just use it. In future you may decide to run flex and it would be 1 less thing required.

[Ben C34]

Flex sensor also measures fuel temp. Which is good.

[CLEM0]

Thank you all for the great replies.

The car plan is straight E85- as the engine isn't in great health with 130psi across all 6 cylinders on a factory 25DET- so low compression.

I want to prolong it while I save up for a rebuild. But I do hope for mid 400whp with E85 in the meantime.

I am thinking about not using the Flex sensor- unless the tuner will drop a bit of 98 in the tank to bring it down to say E60-70- but they'd probably not do this and just tell me to get a flex fuel tune.

I haven't put it in yet and $250 back into my bank account will certainly be beneficial to me right now.

So basically a good idea if running flex, bad/pointless if running straight E85 since it won't effect knock anyway- only stoich point- that's the summary i've got.

[Murray_Calavera]

35 minutes ago, CLEM0 said:

Thank you all for the great replies.

The car plan is straight E85- as the engine isn't in great health with 130psi across all 6 cylinders on a factory 25DET- so low compression.

I want to prolong it while I save up for a rebuild. But I do hope for mid 400whp with E85 in the meantime.

I am thinking about not using the Flex sensor- unless the tuner will drop a bit of 98 in the tank to bring it down to say E60-70- but they'd probably not do this and just tell me to get a flex fuel tune.

I haven't put it in yet and $250 back into my bank account will certainly be beneficial to me right now.

So basically a good idea if running flex, bad/pointless if running straight E85 since it won't effect knock anyway- only stoich point- that's the summary i've got.

Why would you want to tune the car on e60-e70?

I don't think anyone said it was bad or pointless to use a flex sensor if running pump e85 100% of the time. 

I would say the summary is closer to - 

* Yes you can run the car on pump e85 without a flex sensor

* There are benefits to using a flex sensor even if you are always on pump e85. It's up to you if you think those benefits are worth the very small outlay to install the flex sensor.

 

[CLEM0]

5 minutes ago, Murray_Calavera said:

Why would you want to tune the car on e60-e70?

I don't think anyone said it was bad or pointless to use a flex sensor if running pump e85 100% of the time. 

I would say the summary is closer to - 

* Yes you can run the car on pump e85 without a flex sensor

* There are benefits to using a flex sensor even if you are always on pump e85. It's up to you if you think those benefits are worth the very small outlay to install the flex sensor.

 

Thank you- that came across better than how I summarised it.

I would not be getting the car tuned on 98, and if E45 and E85 are minimal in regard to knock resistance, then if I got a bad batch of E85 it wouldn't be detrimental to the performance or safety of the car- so essentially unless I do plan to run flex/98, the only benefit i'd get is consistent fuel trims/AFR and more consistent economy/cold starts.

[Dose Pipe Sutututu]

Install the flex sensor.

One day you're going to rock up to United on a low tank of fuel thinking you'll fill up, then to find out their tanks are empty.

Now you have probably 5L of fuel left in your tank and wonder how you'll get home. That tow truck emergency call out fee + towing fees will cost more than your flex sensor.

 

[Kinkstaah]

There's no real downside and it's not strictly required. Caltex used to serve E70 to E85. As Bill mentioned up above, United has been E80-85 pretty much forever. Never ever saw that change. I suppose the offensive price gouging for the product is worth something.

(then again, Ethanol lowers the price of 91... so... they're probably maximizing the 'cheap stuff' by keeping that Ethanol content up in E85)

[joshuaho96]

1 hour ago, Murray_Calavera said:

Why would you want to tune the car on e60-e70?

I don't think anyone said it was bad or pointless to use a flex sensor if running pump e85 100% of the time. 

I would say the summary is closer to - 

* Yes you can run the car on pump e85 without a flex sensor

* There are benefits to using a flex sensor even if you are always on pump e85. It's up to you if you think those benefits are worth the very small outlay to install the flex sensor.

 

E30 is popular in my area to bump up octane enough to make enough power on our terrible fuel quality in California while not suffering too much of a range deficit. It also helps with not destroying HPFPs in GDI applications.

[GTSBoy]

Be aware that a worn set of rings will let more water-filled blowby gases into the sump. You will want to change your oil close to twice as often as would normally be expected for E85, unless you're happy for it to all go to shit down there.

[CLEM0]

On 3/22/2023 at 2:10 PM, GTSBoy said:

Be aware that a worn set of rings will let more water-filled blowby gases into the sump. You will want to change your oil close to twice as often as would normally be expected for E85, unless you're happy for it to all go to shit down there.

Thanks.

I did a wet test and it jumped about 7-8psi. So i'd say rings aren't amazing.

How often would you suggest a change in oil?

[Murray_Calavera]

As a rough guide - 

Street driving? Every 5,000km.

Track use? Some do it after each track event.

 

[Dose Pipe Sutututu]

7 hours ago, CLEM0 said:

How often would you suggest a change in oil?

When it smells like fuel and/or looks milky from E85 and/or when it's a dark colour.

[Kinkstaah]

10 hours ago, Dose Pipe Sutututu said:

When it smells like fuel and/or looks milky from E85 and/or when it's a dark colour.

I dunno about the smell, oil will smell like E85 if you do so much as drive it out of your driveway... 

[Dose Pipe Sutututu]

11 minutes ago, Kinkstaah said:

I dunno about the smell, oil will smell like E85 if you do so much as drive it out of your driveway... 

jesus, how much enrichment do you have on cold start? lol...

 

[Kinkstaah]

2 minutes ago, Dose Pipe Sutututu said:

jesus, how much enrichment do you have on cold start? lol...

 

Not sure, I have no need for Expensive-Gouge-Juice anymore, though I do have the capacity.

I remember not needing to touch any of the enrichment tables for start with the ol Haltech PS2000. Would start perfectly with full ethanol in the middle of winter without any issues. Never had any cold start problems at all, or hot start for that matter, was the most overblown 'problem' E85 ever had. At least for me..

But ye, do an oil change then drive for 100km then smell the oil filler cap. It smells like E85 really fast in my experience and isn't an indicator that the oil is ready to be changed yet.