92 GMC 3/4 ton 5.7 Poor fuel economy

92 GMC 3/4 ton 5.7 automatic transmission Poor fuel economy
This truck went from 17mpg to 7mpg during one tank of driving. I've changed the O2 sensor and the catalytic converter was removed many years ago. Other than the poor fuel mileage and a slight fuel smell when driving (no visible leaks) the only other symptom is sooty plugs that need to be cleaned every 2 months. The computer does not throw any codes.
Got any ideas?
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Replace air filter. Weak fuel pump. Dribbles instead of sprays (just a guess).
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Christopher A. Young
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Pump has good pressure (truck runs great at all loads) replaced filter spray looks great under timing light and regular light. I'll try an air filter but the one that's on it is less than a year old. Anybody had a problem like this that required a computer replacement?

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just me wrote:

How about a tank of bad gas with water in it. It can knock the socks off a engine quick.
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not bad gas, I've been putting up with this for nearly 6 months.

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"This truck went from 17mpg to 7mpg during one tank of driving."
Seems to me like you need to get your story straight. Either that, or it takes you 6 months to use a tank of gas.
Dave
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His story could still be straight. Say it was typically getting 17MPG tank after tank. Then all over the course of one tank of gas, (probably measure his milage at each tank fill like most of us without computers do), it drops to 7MPG. Then for the next 6 months, it remains around 7MPG after multiple tank refills and does not improve.
I think his logic was that he is ruling out a bad tank of gas because many subsequent tanks have not resulted in an improvement. That would rule out bad gas as a DIRECT cause of a problem (assuming he is not continuing to use bad gas) but it doesn't rule out that there was something bad in the 1st tank of gas at the start of the problem that caused damage to something that is now the direct cause of the problem.

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