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Jim Grant's Tech Tips
88 Honda
Accord: A Pregnant Mother Worries
Q: I have a 1988 Honda Accord I bought used 4 months ago (not fuel
injected). When driving in wet weather, the car will lose power often
from 60 mph down to 20 mph, with bucking and power loss. No matter how
much I downshift or how much gas I give it, there's no change in power
whatsoever. The garage told me that it was the fuel pump, which we replaced,
only to find power failure with the next rain. I've checked with 3-4 other
garages and nobody seems to have a clue as to what the problem could be.
I'm frustrated
in that this is too dangerous to drive, I'm 7 months pregnant!
A: It's
likely that your Honda has a defective TAC system, Thermostatic Air Cleaner.
The TAC system's job is to maintain the temperature of the air entering
the engine and is found on nearly all carbureted and many fuel injected
vehicles.
The TAC system
has three main components: a temperature sensor, vacuum motor and blend
door. At the inlet of the air cleaner, there are two paths for air flow.
One is for air from the front of the vehicle, the other, for heated air
from a shield on the exhaust manifold. The air temperature sensor monitors
air temp inside of the air cleaner, in turn, it controls the vacuum motor
that opens or closes the blend door to control air temperature entering
the engine. Why is this done?
Warm air
weighs less than cold air, so the volume of air entering the engine will
change based on the temperature of the air. The carburetor doesn't allow
for this, so the air/fuel ratio can change just on air temperature alone,
causing a variety of driveability problems. Maintaining a constant air
temperature improves driveability and gas mileage.
Liquid gas
must be vaporized before it goes into the engine; this causes a drop in
air temperature in the carburetor. Have you noticed that when you spill
alcohol on your hands how it feels cold? That's because it takes heat
from your hand and boils off, changing from a liquid to a gas. The cool
feeling occurs because heat is absorbed from your hand. The same cooling
effect occurs with gasoline.
Now combine
low air temperature (under 60 degrees), plenty of humidity (rainy day)
and the wind-chill of 200+mph (airflow through the carburetor) the moisture
in the air is going to freeze and collect in the carburetor. This is called
carburetor ice. Usually driving at highway speed on cold damp days will
cause carburetor ice, which produces bucking, loss of power and even stalling.
The condition rarely occurs during low speed, in town driving.
The parts
for the TAC system are not costly and easily inspected. If repairs are
needed you will feel the difference in improved driveability and gas mileage.
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