What would be the top three causes of very poor fuel economy on a 5.7 liter V8 with TBI. .

1987 CHEVROLET SUBURBAN
130,000 MILES
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JACKMM
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Truck runs good, idles a little rough. I recently changed the spark plugs and cables which helped a bit. Fuel pump and filter changed a year ago.
Sep 19, 2012 at 6:48 PM
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CARADIODOC
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1. Rough idle is due to a misfire caused by loss of spark, fuel, or compression. That's an obvious cause of loss of power and the need to push harder on the gas pedal.

2. Leaking fuel pressure regulator.

3. Dragging brakes.

All of the potential causes depend on what you mean by "poor fuel economy. Is it down by four miles per gallon or are you getting four miles per gallon?
Sep 19, 2012 at 7:33 PM