Date: Fri, 14 Mar 2003 10:30:39 -0800
Reply-To: Mark Keller <kelphoto@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@SHAW.CA>
Subject: Maximum engine power and Performane Chip Discussion
Content-type: text/plain; charset=us-ascii; format=flowed
Vanaganeers,
I've seen these performance chip claims and counter claims before and
feel I should make some comments in light of my observations on the
ECU's final fuel mixture settings during closed and open loop
operation, and yes I have said this before, but for the new
listmemebers... First a little background about the Digifant Fuel
Injection, 86 - 91 vans.
As with any engine, there is a finite amount of horsepower available.
These are the posted numbers we all compare from engine to engine.
Torque and Horsepower and at what RPM. On this comparison alone, the
waterboxer and inline engine numbers cc for cc are really quite similiar
in the normal 2400-4000 RPM range of operation. In the real world
however, the waterboxer does not produce this power without necessary
maintance to the Fuel Injection system and ingition system-- A good
first step in any event. You can read more about this by seaching the
archives 1998 and on under my email address or pmail me.
Now even if the fuel injection system and ingition were properly set,
the O2 sensor Digifant Fuel Injection system still DOES NOT, make the
maximum horsepower possible with the stock engine . This is because the
ECU / O2 sensor configuration of the system is to keep fuel mixture
within a predetermined mixture range-- neither optimum economy nor
optimum power. But rather slightly above average economy and power
mixtures, which equates out to a specific emmision profile. The only
exception being when the throttle is wide open. Then a micro switch by
passes The O2 sensor input and a predetermined mixture is delivered,
giving a BEST available power. Lift off the throttle slightly and you
go back to average power.
Because the Vanagon engine always operates at high percentage of it's
available power, compared to cars, the ability regulate when the engine
makes maximum horsepower is a key to drivability in traffic.
Unfortunately, if true maximum power mixture was availabale at all
times fuel economy would suffer. But if we could have power mitxure
become available from half throttle on greatly changes the way our vans
perform in traffic drivabiliy. Unfortuanely, max power is only
available at wide open throttle-- a hard way to drive in traffic. This
is can make the vanagon much more difficult to drive in some traffic
situations. It's really sad because extra horspower is available, but
the ECU program isn't configured to give it you, here's why.
The Digifant Fuel system works largley by monitoring input from the O2
sensor. By monitoring the O2 sensor with an averaging multimeter you
can see the average fuel mixture theengine is actually getting. Because
the engine is constantly getting a little less and a little more than
this average, it probably isn't even producing the same power it could
if it got a constant mixture.
If you have a well tuned system, you can observe this, by driving at
just less than full throttle up an incline on a couple of minutes
durataion with and without the O2 sensor connected. Your ending speed
will always be slower with the O2 connected. In testing My system, the
ECU/ O2 sensor averaged .53 volts. WITHOUT the O2 engaged, my system
stayed at .84 volts steady throughout the entire climb, essentially a
full power mixture. I also observed that fuel mixture was steady and
varyed nicely according to load. At half throttle about .7 volts, and
1/4 throttle .3 volts and so on. Unforturnatly it's not advised to
operate in this open loop mode even if it gives a perfect control over
engine power. The reason is the Catalytic Convertor could be damaged if
the system malfunctioned and delivered to much fuel. So the question is
how to accomplish this feat with the O2 sensor operating.
As I'm not a programmer I do not know the intracacies of the Vanagon's
ECUs. I state what I'd like to see, and the state what seems to be the
CHIP approach we have presented to us. First what I'd like. A chip
that could set a desirable fuel mixture based on the AFM flap position.
During acceration the mixture should begin to become more power
oriented, at Cruise more economy. Having seen the AFM circuit board,
several points of resistance change made during the wiper arms travell
for idle to wide open. The Chip should use these as triggers to smooth
the transition from economy to a max power. The economy/Max power
transition point should 1/2 throttle. At just above 1/2 throttle The
chip should begin setting a power mix, .5 volt and have full power in by
2/3 throttle, .84 volts. On the economy, just below 1/2 throttle fuel
mixture should be set for .4 volts down to .3 by 1/3 throttle. Real
world, an improvement would be just to have two maps that change at half
throttle.
If the above senario were not possible then I have to guess or speculate
on what a chip programmer is doing . The simple route would be for the
chip to interpret the TEMP II sensor as reading a slightly colder, and
therefore richer fuel map, engine that the stock chip. This of course
would lead to lower fuel economy, as the engine does not need the
powerful mixture when just cruising along, so extra gas is being unused.
A More sophicsticated approach might incorporate new upper and lower
control values on the mixture. I've observed .3 volts, and .7 volt as
the stock values. Knowing that best power is .84 volts, the chip could
allow the mixture to go further up to .84 volts before beginning to lean
out the mixture would tap some power. This would give improvement in
power and lower fuel economy.
My feeling at the moment is if the chip could alter mixuture limits
based on load then we have a better drivability and economy over a
properly tuned stock system If the Chip solution that doesn't addresss
WHEN max power is availble, it dosen't address our needs.
Sincerely,
Mark Keller
91 Carat
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