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Jim
Grant has been working in the automotive industry for over twenty
years. In addition, Jim is an ASE Master Technician with advanced
L/1 certification. He works as manager and technician in his
family's automotive business in New Hampshire. He writes weekly
automotive consumer columns and is editor of an automotive newsletter
that is circulated throughout North America. |
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Jim Grant's Tech Tips
93
Dodge Grand Caravan, Transmission or Engine Problems?
Q: I have a '93 Dodge Grand Caravan, with a
3.3 liter engine and automatic transmission. It presently has approximately
150,000 miles on it. For about a year now, sometimes for a couple of months
at a time, and definitely not all the time, it will run very rough. It
won't shift into second gear when it should, it will "clunk"
when down shifting, it will surge or feel like it isn't getting enough
gas when you're cruising. It almost feels like water in the gas, that
type of rough running. But... not all the time. Sometimes just for a couple
of days at a time. You can drive six miles without a problem, shut off
the car, restart it, then it will be awful. A transmission shop has looked
at it and says the computer does not show any malfunction. Our regular
mechanic can find nothing, mostly because it never acts up when trying
to diagnose the problem. Gas, weather or any other variable doesn't seem
to matter. It has only stalled twice when running rough, otherwise we
just go ahead and drive it! It almost seems to me that if you start the
car and it happens to be at the wrong time in a cycle, it acts up. What
about an oxygen sensor? I would certainly appreciate your help..... Sara
A: Your
vehicle has a computer for the transmission and another computer for the
engine. When your technician was checking the engine did he/she check
the engine's computer, for any diagnostic trouble codes? An automatic
transmission will not operate correctly if there are engine problems.
Make that a computerized transmission, and the problems are compounded.
The engine has to be running correctly before the transmission can. You
said, " It almost seems to me that if you start the car it happens
to be at the time in the cycle, it acts up ". Have you tried shutting
the engine off for a short time and restarting it when this happens? There
are sensors that tell the engine computer where No. 1 cylinder is and
how fast the engine is turning. If this information gets jumbled-up the
engine will run erratically. The transmission computer shares the same
information, it too becomes lost in knowing what to do as well. A problem
with this sensor is caused by engine oil leaking into the electrical connector.
The engine oil interferes with the electrical signal, confusing the computer,
which isn't smart enough to realize it's being confused. A closer inspection
of the sensors that make the engine run may provide an answer to your
problem.
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