Date:         Mon, 8 May 2006 10:13:45 -0700
Reply-To:     John Bange <jbange@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Bange <jbange@GMAIL.COM>
Subject:      Re: Engine modifications needed to run E85?
In-Reply-To:  <385C6D3C-D615-4804-9935-EE9DFB6769FC@lpl.arizona.edu>
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>
> Does anyone know what modifications would be needed
> to the digijet system to make it compatible with E85?


A tweak of the timing, an adjustment of the AFM, and an inspection of the
fuel system for alcohol-sensitive parts is about all you actually NEED.
Alcohol has about 30% less energy per unit volume than gasoline, so you need
to adjust the air metering for closer to 8:1 AFR or so to get the O2 sensor
within self-tuning range. There's some debate over how bad it is to expose
unprotected aluminum to E85 and its combustion byproducts, but I think the
practical upshot is that it's not enough of a problem to worry about short
term.

I suspect the injectors might need to be replaced,


It's not necessary, but your fuel flow at "max power" will be the same while
your fuel has 20-30% less energy content, resulting in a loss of power. If
you want the same amount of top end power, you'll need injectors that
deliver a 30% or so greater volume of fuel per unit time over theI stock
injectors. If you change injectors like that, the AFM won't need as much
adjustment.

is the
> fuel pressure a consideration?


Always a consideration with larger injectors, but I've never heard of anyone
having problems unless the pump was already weak. Most FI fuel pumps have
plenty of capacity. They generally seem to build them for high pressures and
then let the pressure regulator take care of sending the excess back to the
tank.

  What about the catalytic
> converter?
>

If everything's tuned properly for E85, the cat will be fine. Some opine
that a badly tuned gasoline engine is worse for a cat than a badly tuned
alcohol engine.

Whether or not it's worth converting, I think that depends entirely on two
things: 1) the availability of E85 and whether you can switch to using E85
only; and 2) whether E85 is cheap enough to be worth switching to: with
20-30% less energy per gallon, you need to be paying 20-30% less just to
break even.  The fuel injection systems on these old wasserboxer engines
isn't really suited to "dual fuel". The O2 sensor is a narrowband model that
requires manual adjustment of the AFM for "coarse tuning" in order for the
sensor to be able to effectively manage "fine tuning". Unless you convert to
E85 exclusively, you'll be stuck dialing in your AFM every time you switch.
In order to have a really effective and convenient dual-fuel system, the
best way is to pull the Digijet/Digifant and its narrow band O2 sensor and
put in something like a Megasquirt with a wideband O2 sensor, which can have
multiple, selectable "profiles" for whichever fuel blend you are filling
with. The only drawback with that is that you can't really do any mixing,
lest you end up with a mix that's something like "E43", for which you have
no preset profile. If you intend to switch fuels more than 2 or 3 times a
year, or want a true Flex-Fuel Vehicle, you'd need a "fuel composition
sensor", which measures the alcohol:gasoline ratio and tunes the fuel
injection system on the fly. The one drawback to the Megasquirt system is
that it's not an off-the-shelf product, but rather an "open design"
hobbyist/DIY sort of thing. You can buy pre-built MegaSquirt hardware kits,
but the installation and configuration is still entirely up to the end user,
and requires quite a bit of technical diddling to get it running. Definitely
a "project" rather than simply an "upgrade". <http://www.megasquirt.info/>
(type "e85" in the search box for specifics on MegaSquirt and flex-fuel).
Interesting stuff. I wish I had time to climb the learning curve. There's
even a very active "MegaSquirt List" you can subscribe to. I wonder what
their equivalent of a "tire thread" is? You just KNOW they gotta have at
least one...

--
John Bange
'90 Vanagon - "Geldsauger"