Poor performance

1978 GMC SIERRA
100,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC
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AWR
  • MEMBER
  • 1 POST
Truck runs bad and using up all the gas ( about 2-4 mpg). Ran okay when purchased but it sat for nine years so now everything has been going bad. no matter what I fix something else goes wrong.
Feb 16, 2019 at 12:25 PM
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JACOBANDNICKOLAS
  • ✓Experienced Mechanic
  • 110,246 POSTS
Hi and thanks for using 2CarPros.

Wow... Not sure where to start. If it sat that long, it isn't uncommon for things to go bad when it's put back into service. However, the fuel mileage is really bad.

First, are you certain there are no fuel leaks? Is there black smoke from the exhaust? Has the vehicle been tuned up? Does it still have catalytic converters on it?

Let me know the answers to those questions. Also, here are a few links you may find helpful. The links are designed for newer cars, but the same basic principals apply.

https://www.2carpros.com/articles/engine-black-smoke

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Let me know.

Joe
Feb 16, 2019 at 2:00 PM
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