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Jim Grant's Tech Tips
93 Fiat,
Bunny Hops From Downunder
Q: My brother owns a 1993 Fiat Tempra 1.8xie which has done about
70,000 km and, in the last 12-18 months, has developed a cold starting
problem which the local specialists have been unable to rectify. The symptoms
are that the car produces some monumental "bunny hops" every
time you reapply your foot to the accelerator after taking it off (this
only happens when the car is cold). It is fuel injected, so we suspect
that this might be involved, but no one has been able to pinpoint how.
Any suggestions would be appreciated!
Thanks from
downunder.
A: Your
suspicion of a fuel related problem may be on the right track. I have
one problem. Currently there are no Fiats being imported into the U.S.
which means information sources are not readily available. Not all is
at a loss; there are rules of operation that apply to any vehicle in either
hemisphere.
You state
the condition is temperature related, only occurs when the engine is cold.
It is also related to throttle movement, but only after accelerating then
reapplying your foot to the accelerator.
My thoughts
are two part: First, check for sticking emissions controls or emissions
controls that are operating, but are not suppose to be when the engine
is cold. These component’s operation can be monitored and compared
to the manufacturer designed operation. Second, a restricted vacuum hose
or passage that is delaying information to the fuel injection, computer
or emissions controls. Letting off the gas pedal causes engine vacuum
to rise. Stepping on the gas pedal again causes vacuum to drop. If a vacuum
hose or passage is restricted, the information that the vehicle’s
fuel injection, computer or emissions control use may be delayed. The
result is momentary confusion with possible bunny hops, until things balance
out.
Diagnosis
will require a technician who has a good working knowledge of your vehicle.
Be mindful that the diagnostic window (time) he/she has to identify your
problem is limited to cold operation, 5 minutes running time.
By the way,
what does a car look like when it’s doing the monumental "bunny
hop"?
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