Date: Sun, 1 May 2005 11:19:21 -0400
Reply-To: Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: HELP! Westy Stranded in Bryce Canyon National Park...
In-Reply-To: <4274E9A3.2090308@charter.net>
Content-type: text/plain; charset=US-ASCII
The major cause for power loss is the reduced cylinder charge. Not only
does this reduce the air or air/fuel available, it also reduces the
effective or dynamic compression ratio. The rate is 3%/1,000 feet. So at
10,000 feet, a normally aspirated engine has lost 30% of its power. As
for compensating for altitude or oxygen content, the only compensation
available on the Vanagon is the O2 sensor. There are many cars with
barometric sensors, but not the Vanagon. However, the real problem for
the no-start most likely is that something is actually wrong. The excess
fuel to the point that it can be smelled at the exhaust indicates a
serious flooding problem. Assuming engine compression is good, and there
is good healthy spark, the fuel pressure regulator, temp2 sensor, and
even the ECU is suspect. I have seen these ECU short out the output
device and have the injectors spray continuously. Some real
troubleshooting, not guessing is needed.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of John Rodgers
Sent: Sunday, May 01, 2005 10:37 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: HELP! Westy Stranded in Bryce Canyon National Park...
Not to beat this to death, but....
If I understand our vans and the FI systems, the ECU has sufficient
capacity to maintain proper fuel/air ratio regardless of altitude or
temperature.
A hot summer day at altitude would be the worst of all conditions, as it
would tend to send Density Altitude right off the scale. 10,000 feet ASL
becomes 12,000 feet ASL at a high temperature - for performance
performance purposes. If the engine is in good condition, proper
condition, at sea level, then at those higher density altitudes the ECU
should be able to maintain that proper fuel/air ratio.
The problem of decreasing performance at altitude is due to the fact of
less dense air. As the air becomes less dense, the engine ttends to run
more and more rich as altitude increases. The ECU adjusts the fuel air
mixture to proper ratio, but it does it by reducing the amount of fuel
to match the air available. At altitude with the air thin - less oxygen
per pound of air than at sea level - the reduction of fuel to match
results in a power loss. So if you van is very peppy at sea level, don't
expect it at altitude, especially out in the west in summer.
As a side note, the Density Altitude is a matter of serious concern to
aircraft operations. Lift generated by the wings of the aircraft is
related to speed, and an airplane must have sufficient speed to lift off
the runway and to gain altitude. At high density altitudes the airplane
must have a runway long enough to allow the airplane to accelerate to
the higher speed required. To accomplish that higher speed, it must also
have sufficient engine power. With the loss of power, from the effects
of altitude and temperature, combined with the need for additional speed
to achieve liftoff velocity, and the subsequent additional runway
required to allow enough time to reach that liftoff speed, it can become
very problematic for an airplane to even be able to get off the ground.
So, there are all kinds of tables, charts, and considerations for a
pilot to make or refer to , so as to be able to make a decision about
the safety of the flight about to be attempted. One of the first steps
to attempt to overcome such difficulties was to add a supercharger to
the engine to get the power back up. With a supercharged engine, the
power is maintained, acceleration is faster, and lift can be achieved to
get the airplane off the ground within the confines of the runway. Later
came turbine engines, which improved matters even further. But even so,
pilots to this day must be concerned about the relationships of
temperature, aircraft loaded weight, engine power available, etc.
How does all this relate to the Vanagon. Expect less power at altitude
unless the engine has been turbocharged. That is the main thing. One
might also expect an increase in gas mileage at altitude - high density
altitudes mean lower air resistance....plus the reduced fuel consumption
when the ECU reduces the fuel to keep the fuel/air ratio correct. But
again, if the engine is turbocharged, sea level power could be
maintained so fuel consumption would not change. Gas mileage might
improve slightly due to lower air resistance.
My $0.02 for the morning.
John Rodgers
88 GL Driver
Chelsea, AL
Jeff Oxroad wrote:
>In a message dated 4/30/2005 5:14:06 PM Pacific Standard Time,
>camper@TACTICAL-BUS.INFO writes:
>
>Here in colorado it is possible to get different blends according to
the
>altitude. But that blending is for emissions and your engine should
run the
>same either way if the O2 and AFM and ECU are working correctly.
>
>
>
>I have to respectfully disagree, and I do so with no ill intent and no
ill
>will. But instead to set the record straight.
>
>You are correct that the high-altitude blend of gasoline has a posative
>effect on emissions. However the theory that there's no effect on the
engine's
>ability to run correctly doesn't fit the above conclusion. The idea
that a
>different blend effects the emissons but not how the engine runs is
flawed. This,
>because how the engine is running is directly responsible for the
emissons.
>A "correctly" running engine--one running under ideal circumstances--
will
>produce lower emissions than one running under poor conditions. The
>configuration is also then contigent on the blend of gasoline and the
altitude.
>
>The gasoline blended for a specific altitude is concocted with
consideration
>to the amount of oxygen in the air. The guy who's stuck in Bryce is
very
>possible having a problem related to the fuel system. He stated he can
smell
>fuel. Therefore let's say for arguments sake his bus is getting too
much fuel
>for the amount of oxygen at the altitude were he is camping. This is
likely
>because the fuel in his tank is mixed for a lower altitude. In essence
the
>engine is getting too much fuel to start--it is "flooded." It is
running rich we
>would say if it were running. or now we can say it's too rich to
start.
>Why--because they're ain't enough oxygen to create a favorable
situation for
>combustion with the higher octane fuel. (and I'm not willing to agree
that the
>difference in the high altitude blend of fuel is soley an issue of
octane.
>Although this is certainly the most notable difference to the consumer
since it is
>printed at the pump.)
>
>Granted this lack of combustion--or even if he got the engine to
>tstart--creates an unfavorable emissions output. But this emissisons
problem is
>precisely the same problem that is keeping the engine from starting:
poor combustion.
>One is the same as the other.
>
>I would almost agree that if everything is working properly this might
not
>be a crucial concern. So I'd say if the guy stuck in Bryce drove his
Westfalia
>off the dealer's lot in 1984 and headed to the Canyon with a lower
altitude
>fuel he'd likely be up and running and we wouldn't be here hashing
this out.
>But 21 years after that bus came off the lot, that extra rich mixture
might
>just be enough to leave a guy stranded. And quite frankly it may have
been
>enough to leave him stranded him in 1984.
>
>Therefore I still recommend fueling up every 1,000 feet you gain in
>elevation. Also a fresh tune up when heading to a higher altitude will
help.
>
>Disclaimer: The fellow in Bryce Canyon could be suffering from a host
of
>problems. The altitude vs. gasoline is not necessarily it. But it's
worth
>examining.
>
>Best,
>83.5 Westfalia
>LA,CA
>
>
>
>
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