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1992 3.1 Lumina, crappy gas mileage lately


Chris2012

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could expect to get at least 18 around town w/the a/c going all day. Lately it's down around 15. car has 180k.

 

I _did_ disconnect my battry recently, turned up dead a couple of times, checked current draw. Did I reset the computer, and force it to "learn" while driving in hot weather (w/ac going)? I think I've only disconnected my battery previously in cold weather.

 

Also added some new/used tires. MUCH nicer treads, although left rear wobbles or otherwise acts up a bit (intend to get the balance checked, but I suspect it might be something else, belts slipping or something).

 

Help. I used to get around 300-320 per tank. Now it's closer to 220-240 per tank. This STINKS!

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Did you try doing a tune up? Plugs, Wires, Fuel, PCV, Air, Filters, Belts, Hoses. When was the last oil change? Is the car running at proper temp? Proper air pressure? Whats the weight loads in the vehicle? How do you drive the vehicle? The A/C system will drain it a bit, if your running it all the time, and depending on how you drive, it will considerably take much of your fuel. Also might i suggest maybe after a tune up, run a tank of 89 in the vehicle. 89 contains some fuel system treatments that could help out. Also how the exhaust system? Your cat might be taking a plunge. Have you ever performed a decarb or seafoam treatment on this vehicle? Cleaning out the throttle body, egr, etc might help a bit if its gummed up in there.

 

There is a few factors that could negotiate your fuel mileage.

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How does the car seem to be running? Any hesitation/rough idle? On my '90 3.1 Celebrity, I was getting bad fuel mileage out of it, about 16mpg, along with a rough idle/misfire and hesitation. Since I had just gotten the car I I decided to do plugs/wires as a start. Of course it turned into a bigger project as I dug in further... after pulling my upper intake plenum to clean out a mouse nest (and have easier access to replace the oil pump drive which was leaking oil), I got curious and ohmed my fuel injectors. Found 3 of them that were below where they should be (12 ohms). Replaced the bad injectors along with the plugs/wires and the idle improved greatly, and my mileage went back up to about 21-22 overall (the car is about 50/50 highway/stop &go). Not sure what one thing got my 3.1 running better since I replaced quite a bit all at once but I think possibly it was those bad injectors, so check them out with an ohmmeter.

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