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Jim Grant's Tech Tips
90
Chevy Lumina, Stalling Problem
Q: I have a ‘90 Chevy Lumina with 100,000
miles, auto tranny. I drive it for about 30 miles and it will then stall
when I come to a stop sign. It will restart, but when I drop it into drive,
it just dies. I let it sit for about 5 minutes and then I can restart
and drive. However, after another 10-15 miles it dies again when I come
to a stop. It restarts and dies once again when I drop it into drive.
Please help this single mom who needs a dependable car. Thanks.
A: Well
Mom it sounds as if you have the classic sticking lock-up torque converter
solenoid problem. Your vehicle, like most with automatic transmissions
today, has the ability to lock-up the torque converter. Of course the
next question is what is a torque converter? The torque converter is the
device that allows you, with the engine running, to select a reverse or
forward gear without the vehicle moving or stalling (when working right).
Then when you accelerate the engine, the transmission fluid in the torque
converter transfers the energy from the engine to the transmission. No
parts are touching, it’s just the moving oil that causes the vehicle to
move.
It doesn’t take a rock hunter to realize that the engine will always be
spinning faster than the transmission to make the vehicle go. This is
not too fuel inefficient at highway speed. So to get better gas mileage
the inside parts that don’t touch in a torque converter are locked together.
Thus the name lock-up torque converter.
The lock-up of the converter is a computer based decision; "Yes a computer
has to get into the act". The computer commands an electric solenoid in
the transmission to lock-up or unlock the converter. The problem we see
is with that solenoid, it sticks! When it sticks and you’re coming to
a stop, the engine will start jerking and stall. The engine will start
right up, but the moment you put it back in gear it will stall again.
Let things set for a moment and off you go like nothing ever happened,
until.
To prove that the solenoid is the culprit it can be disconnected electrically
and the vehicle can be driven to see if the condition reoccurs. You’ll
note a drop in gas mileage during this time. Replacing the lock-up solenoid
is not a difficult or costly job and is the likely cure to your stalling
problem.
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