We live in the mile high city - the greater Denver area.
There's about 12% less oxygen and air pressure here and I understand that
cars get about that much less gas mileage because of it?
The tail pipe sure is black, I know that's not an objective standard or
But we have this 93 Corolla and were wondering of a low cost air blower
could be added before the air filter, so that it would regulate the input
air pressure to that of sea level?
Can that be done cost effectively?
We sure wouldn't mind saving 12% on gas, if it didn't cost much to do.
What you are talking about in essence is a "poor man's" supercharger /
turbocharger. You will be boosting the ambient air pressure. This plan
will eventually take it's toll on engine components that are not
designed for any boost and substantially reduce your engine's life. Do
you have a plan for any controls for the system to control the boost
pressure? A better plan for you is to take the car to the dealer and
have them re jet the carburetor to your driving environment. This is a
normal problem and they are usually quite well versed in this adjustment
and probably do it very accurately. If the 93 Corolla has fuel
injection, you obviously have a problem with it as you mentioned the
exhaust pipe is black. Many people have move from one local to the
other, experienced this condition, and have had to have this adjustment
performed on carbureted vehicles. Your engine will thank you, and you
will be rewarded with fuel savings, and better performance.
If you have the EFI system, it will automatically compensate for any
altitude and or barometric pressure changes, and adjust the fuel to
maintain a perfect air to fuel ratio (14.7 : 1). You need to take your
car in for service.
If you have had black deposits in the exhaust system for that long, the
catalytic converter may be ruined, the O2 sensor(s) are probably coated
(coked up) with carbon and your engine is not performing as it should.
My advice to you IMHO, would be to take the car in to a reputable Toyota
dealer and have them troubleshoot the problem. You definitely have
something wrong with the engine. It is not normal to observe black
carbon deposits on the inside of the exhaust system, which usually
indicate a rich (too much fuel) condition. With the EFI system, it
should run flawlessly at any terrestrial ambient condition. If you have
this problem repaired your MPG should improve even from what you get now.
I have driven across Trail Ridge Rd in Rocky Mountain National Park many
times without any noticeable problem. The altitude is 12000 feet. Once I
drove a car up to the top of Mount Evens at 14000 ft, although I was
traveling a pretty slow speed, so I don't know if that is fair test.
This is true if the amount of fuel delivered to the engine is constant
because the air/fuel mixture will become rich, i.e., too much fuel relative
to the amount of oxygen.
Your vehicle has a sensor that determines how much air is entering the
engine and will adjust the amount of fuel to maintain the correct air/fuel
It is normal for the inside of the exhaust pipe to become black over time.
While the emissions controls do a pretty good job of removing tailpipe
emissions, they do not remove all of them. Mixed in with the exhaust gases
are hydrocarbons, which are unburnt fuel in the form of particulates, or
soot. The particulates eventually coat the inside of the exhaust pipe,
giving it a black appearance.
If your engine was running rich, your car would not pass any periodic
emissions test. Assuming that your car has passed emissions tests, then the
electronic fuel injection system is functioning properly.
As an aside, if you were to add additional intake air through the use of a
fan, turbocharger, or supercharger, the engine control module will sense the
additional air and command additional fuel, so although your car's
performance may improve, your fuel economy may get worse unless you are very
careful to apply less throttle.
"Ray O" <rokigawaATtristarassociatesDOTcom> wrote :
Does that need any special adjustment for the altitude?
Is there a way that I can lean that setting out but adjusting it?
Like I said, not only passed them but 2-3 times at least, the standards.
Here's another question;
Back during the oil & gas crisis of the 70's, people were adding vacuum
gauges to their cars. It would be mounted behind the steering wheel on
They had green, yellow and red zones, so you could lighten up your foot
and get better MPG.
Is there any point in using something like that nowdays? Do they still
sell them for that?
Back when engines had carburetors, you could change the carburetor jets for
high altitude applications to maintain the proper air/fuel mixture of 14.7
parts air to 1 part fuel. A modern fuel injection system, which your
Corolla has, does this by controlling how long the fuel injector sprays
fuel, so at higher altitudes, the injector sprays less fuel than at sea
level for a given throttle position.
There is no way for you to lean out the setting because there is no need to.
The system is programmed to maintain the 14.7:1 air/fuel ratio, which
supports complete combustion of the fuel. If you were to lean the
adjustment to, say, 16:1, the fuel would not burn as completely so you would
be wasting fuel by sending unburnt fuel out the exhaust, and to make things
worse, you would have to depress the throttle more for a given amount of
acceleration or cruising, so fuel economy would go down even more.
If your goal is to improve fuel economy, then modifying the air/fuel ratio
is not the answer because doing so will make fuel economy worse.
If your goal is to improve fuel economy, then the same things that work at
sea level will work at altitude. Try these simple things that many people
1) Use either Denso or NGK brand spark plugs, ignition wires, distributor
rotor, and distributor cap that are recommended for your car and stay away
from other brands. Some other brands may work fine, but many do not so
rather than experiment, stick to Denso or NGK.
2) Check ignition timing to make sure it is within factory specifications,
probably around 10 degrees before top dead center.
3) Make sure the engine air filter is clean.
4) Rather than buying the cheapest gas you can find, stick to a name brand
and buy from a gas station that does a good sales volume to reduce the
chances of sediment getting into your fuel system.
5) Inflate your tires to 5 PSI over the automaker's recommended tire
pressure. This will improve tread life and improve fuel economy by reducing
rolling resistance, with a slightly harsher ride.
6) Remove all unnecessary payload from the vehicle because the engine has to
work to move that payload around. Even 50 extra pounds in the trunk can
make a 1/4 to 1/2 MPG difference.
7) Make sure the engine thermostat opens at the proper temperature. If the
thermostat is stuck open, missing, or opens at the incorrect temperature,
the engine will take longer to warm up, and if the engine takes longer to
warm up, it will run rich for a longer time.
A huge side benefit from a clean running engine is a very efficient engine.
Mess with the engine and efficiency will probably be lost.
The principles behind using a vacuum gauge have not changed, so I suppose
you could still add a vacuum gauge. I think most people could learn to
drive more efficiently just by listening to the engine and changing their
driving habits. The drawback to a vacuum gauge is that you are adding a
potential source for a vacuum leak, which would hurt fuel economy.
Turn off any unnecessary electrical accessories like TV's, video games,
unneeded fog lights, etc. and use the AC sparingly, if at all.
If your car has an automatic transmission, the sooner you back off the
throttle, the sooner the transmission will upshift, and the sooner the
transmission upshifts, the better the fuel mileage. When accelerating while
the car is already cruising, depressing the throttle gradually will reduce
downshifts. The adage that you can improve fuel economy by driving as if
there is an egg between your foot and the gas pedal is true.
Lots of short trips where the engine has to warm up will hurt fuel economy,
as will idling the engine for long periods. If the engine has to idle for
more than a minute and you are not at a traffic intersection, shut it off.
The fuel economy that you posted is pretty good for a 14 year old car,
especially at altitude. I would try the stuff I listed above and drive like
the egg is there, and you may see a 1 or 2 MPG gain.
Ignition timing cannot be manually adjusted on a vehicle with a
distributor-less ignition, but if the car has a distributor ( IIRC the 1993
Corolla has a distributor), then timing can be adjusted.
Timing is kind of adjustable on some engines with a distributor-less
ignition by adjusting with the crankshaft position sensor.
Vacuum gauges have fallen out of favor with consumers because it is very
easy to learn how to drive to maximize fuel economy without one. If you
really want a vacuum gauge, you can get a diagnostic one and snake it into
the passenger compartment and use it until you get the hang of driving
without it, then put the gauge away in your toolbox.
Your car does not have points or a condenser, which is why I did not mention
them under #1 above. The function of the points and condenser is handled
electronically by the igniter (which does not need routine replacement).
I knew you could still get vacuum gauges, although I don't really see a
reason to install one unless the driver is not disciplined enough to drive
with a light foot.
And your car monitors the current environmental conditions among other
things as you drive and constantly keeps the engine running properly.
In other words the car is smart enough to know when you drive up a
mountain and changes all the engine controls automatically for you.
Not with a correctly functioning EFI system. All consumer fuel injection
systems are designed to adjust the fuel air ratio to perfect
stoichiometry for gasoline.
Then your engine is performing at normal standards, that is good.
Perhaps a bit, but nothing abundant, and as you mentioned, it passes
No, it really does. They are designed and tested to do so.
Or, waste a lot of money on some after market rigged system that isn't
going to address your problems.
You may want to consider selling it and buying something that is more
suited to the power and MPG targets you are looking for, perhaps a car
that is supercharged or turbocharged. But, of course, it's your call.
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