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Fuel system

Tiny
FARMERJOE
  • MEMBER
  • 1992 CHEVROLET CAVALIER
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
Sirs: We just replaced the fuel pump and front struts. The fuel pump works great and the front end is good after alignment. My problem is that after the above work, the gas mileage went bad. I have checked the whole fuel system for leaks and found none. This car was getting twenty eight miles per gallon but now is down to about twenty two. The car had a complete tune-up seven month ago and runs good, just the gas mileage went bad. Help!
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Monday, November 13th, 2017 AT 12:18 PM

4 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,770 POSTS
What climate are you in? The mileage on my truck just dropped from 22 to 18 in the last two weeks when the outside temperature dropped into the low twenties.
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Monday, November 13th, 2017 AT 4:40 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,161 POSTS
Yep, if you are in a cold area or worse in a state that has "winter blended" gas it could easily be just that.

Why was the pump replaced?
It is possible that the pump replacement was a result of a different problem that the new pump is now masking. Like a leaking injector or failing pressure regulator.
Testing the regulator is easy, pull the vacuum line off and look for fuel in it. There should not be any. If in doubt, start the engine with the vacuum line off and plugged. If any gas comes out of the port the hose was on, the regulator is bad.

To look for a leaking injector you would need a pressure gauge to watch for pressure drop when the fuel pump stops running.
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Wednesday, November 15th, 2017 AT 3:45 PM
Tiny
FARMERJOE
  • MEMBER
  • 15 POSTS
We replaced the fuel pump because it quit working, after we dropped the tank I attemped to jump the pump with a 12 electrical source and if it ran it jerked and growled and ran rough. I was only running it intermittently so I'm sure we did not burn it up. As soon as the new pump was installed the car started up and ran well'but the mileage was off. Since then the problem has gone away so I'm a little baffled'We did pull the hose of the regulator but didn't get any gas so have to assume it's good. Thanks for your help
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Friday, November 17th, 2017 AT 1:48 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,161 POSTS
Well, It's possible that having the battery disconnected changed the learned values back to "stock" and now it has relearned the sensors and corrected itself. Other than that I can't think of anything that just replacing a bad pump could do that would trigger lower fuel mileage. But if it's working good now that's all that really matters.
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Friday, November 17th, 2017 AT 3:06 PM

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