Jim Grant's Tech Tips
90
Plymouth Sundance, Bad Gas Mileage
Q: I really enjoy your
tech tips column - it's addicting to read. I just bought a '90 Plymouth
Sundance which runs perfectly (engine very smooth with plenty of power)
but only gets 20 mpg. It has a 4 cyl - 2.5 litre engine with 3 speed automatic.
If the O2 sensor fails to generate its 1 volt signal, could it cause a
rich fuel mixture - without affecting driveability?
A: An
O2 sensor can fail in a manner that will cause poor gas mileage. But,
before installing any new parts I suggest checking the basics. It's not
uncommon for the vacuum hose to the Manifold Absolute Pressure (MAP) sensor
to crack, collapse or become restricted. MAP is a fancy name for an electronic
vacuum gauge that the vehicle's computer can read. The vehicle's computer
makes fuel delivery adjustments based on the information it receives from
the MAP sensor. The computer is completely clueless that the information
it's received is incorrect. The result can be increased fuel consumption
with no noticeable driveabilty problems. It's important to be sure the
basics are correct before replacing any pricey computer parts. You can
waste a lot of money guessing.
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