jrp1588

C6 Corvettes and newer have access to Flex Fuel through DSX, but no love for the C5 or even the ubiquitous F-Bodies. Seems like a huge market to completely bypass.

Not sure if it's the same, but with Subarus, kits like these just piggyback off the MAF harness and tweak the MAF values based on the ethanol content from the fuel sensor. This tricks the computer into thinking more air is coming in so it'll inject more fuel to make up for the lower energy density of ethanol. I don't see any reason why this wouldn't work for a C5.

I live smack dab in the corn belt, so I've got plenty of ethanol stations locally, but availability gets sketchy out of town. I really want the option to put in 93 if I need to.

jrp1588

Lack of interest perhaps? Does everyone just bring a laptop with them to swap tunes when they need to?

DSteck

It's not as simple as people would like it to be.

tblu92

Most all GM cars from 2003 and newer already have an ethanol tune in the ECM--The problem with converting an older car to E85 is that the ECM does not come with provisions to pin an E85 sensor into the fuel system-----Every vehicle is different depending on the "operating system " of your ECM On the newer 2014 cars it is a simple 3 wire pinning into your ECM and one of them is a ground---Then all you do is to activate the E85 tune to make it work---On a C5 or a C6 it is far more complicated---

jrp1588

I'm aware the older ECUs don't have any provisions for flex fuel. What I described in the original post was a workaround that the Subaru community has been using in recent years. It just uses a GM flex fuel sensor, and a dedicated computer to adjust the MAF readings based on the ethanol content, causing the ECU to inject the appropriate amount of fuel.

Yes, it's a little hackey, but it works on Subarus. If you know anything about those, they're extremely finicky and love to blow ringlands if their tune isn't impeccable. I would think a a less picky system like the LS engines could use a similar setup without any isues.

Drewstein

My local shop can convert a C5 or F-body to flex fuel, just be ready to pay for it. Generally we only see that need in big HP cars which limits the market. The big HP guys don't want something hackey messing with the MAF with their SD tunes. Not even sure how they would approach that.

Under a certain power level it's not worth going back and fourth and above the level you pay to do it right. There really isn't a market for the middle.

jrp1588

They're probably using an aftermarket ECU, which is a little more involved than I'm wanting to get. I just want a few more ponies and cheaper gas. e85 is dirt cheap around here.

lt1z

You can run E85 flex on the 411 PCM but it isn't as simple as plug n play and turn on in the tune like the Gen IV and Gen V stuff. Be prepared to spend more to make it work.

jrp1588

Again, I get that, but other vehicles that have no native e85 support have kits that get around this issue by tweaking the MAF values. I'm guessing no one bothers for NA cars because there's not as much power to be gained compared to turbo cars.

TurboLX

"Tweaking the MAF Values" is not a proper solution for converting to flex fuel. There is a lot more to it than just lining up the desired AFR on a warmed up engine.

The older ECU does not have the native provisions for flex fuel like the newer modules. Things like starting fuel and spark advance (both WOT and part load) must also be adjusted independently for ethanol.

jrp1588

Neither does an older STi or Evo, but they've made kits for it. Though I don't really understand how they're adjusting the timing advance. The fueling makes sense, but I don't get the rest.I'm actually talking to Delicious Tuning, the makers of the Subaru kits, right now. They said they'd be interested in seeing if it would be feasible, but they need a stock map or a physical ECU to look at. Anyone have ideas where I might find either? Ebay seems to be full of "flash to your VIN" and "ECU Repair" listings. I can't seem to find just a plain old untouched pulled ECU.

RonSSNova

ECU from what? A Corvette?
GM used the same ECU for many applications. Trucks and cars.
The car it is installed in dictates the operating system programmed into the ECU.
Search EBAY for 0411 or 4896 ECU.
They made millions of them.
Should be less than $50.

If they aren't GM guys, I'm not sure how they would know how to power the ECU and read the tune.......although it's actually quite simple.

BTW, go over to the LS Tech site, look in PCM Diagnostics and Tuning.
Flex fuel has most certainly been added to these older ECU's.

Drewstein

It requires an ECU that can take the flex fuel sensor and the older ECUs can't handle them. It's not worth a kit because the people who would use it can just run a stand alone or swap in a computer that works.

No reason to have flex fuel without big power, it's not worth the investment, especially NA.

ysb02

If DSteck starts doing the 2004 computer conversion Vengence/CPR does I'll be beating down his door.

So far for options there's the 2004 ecu conversion, aftermarket ecu, or just running a sensor and shutting down if the ethanol % goes above / far below what you tuned for. I know someone running a 1000+ rwhp GT500 on e85 with no flex. iirc he runs the AEM unit that will tell if you the % is off.

jrp1588

Yeah, I have spoken to a local tuner, and he claims the e85 blend around here doesn't change enough to matter much. He said I should be fine as long as I tune in the summer months when the ethanol content is highest, then it would run rich but safe in the cooler months. I'm going to get a beater to drive most of the winter anyway, but I really don't care to do it unless it can be done right. I've pretty well given up on the idea anyway.

ysb02

I'm tossing around the idea of keeping a 55gal drum of it in a shed and just filling up from it as needed.

I'm assuming the worst thing to do is run lean which would mean running a higher ethanol % than what you tuned for?

jrp1588

Yeah, if you tune in the winter, bu summer the ethanol content is increased, which decreases its energy density causing it to run lean.

Drewstein

I run the 55gal drum for my f-body. It's not driven much so it's the easy way to deal with it.

As I mentioned, unless you're making big power then you don't need an E85 solution. If you're running big power then you need the budget to do so which means you have a shop convert it. Flex fuel on older cars is definitely a luxury.

Worst thing is you drop octane and detonate your motor.

hodge9386

Iv been looking around alot about this and it seems the only way to do it is to convert to a p59 pcm but nobody wants to tell exactly how to do it. From what iv seen the pcms are damn near plug and play but what i havnt figured out is weather or not they will work with the c5 dbw. There is people out there that have made it work but they dont want to tell how they did it.

NSFW

The Subaru ECUs from 2004-2005 and later (depending on model) have two sets of tables for fueling, timing, DBW throttle tables, and other things. With the stock tune, the ECU pulls values from both sets and transitions between them based on a "map switch ratio" parameter. I've never been clear on how the ECUs choose the ratio at any given moment (my '05 has two sets of tables but the ratio is permanently fixed at zero... go figure...) but the tables are commonly referred to as "cruise" and "non-cruise." Some of the newer cars have 3 or 4 sets of tables for some things.

While I don't know the specifics of the Cobb flex-fuel thing, I'm sure it would be possible to re-purpose an existing sensor input and just base the map switch ratio on that. In the open-source hacking community we have talked about using a TGV sensor input, for example. The rear O2 sensor could also work.

TL;DR - Subaru ECUs already have almost everything you'd need for flex-fuel, so you only need to change a little bit of code to make flex-fuel work.

Related question - are there hobbyists involved in reverse-engineering C5 ECUs/PCMs and adding new features? If so, where do they hang out?