godpossessed Posted September 22, 2007 Share Posted September 22, 2007 The last few tanks have been in the 16mpg range in combined driving. We were getting 18-20mpg. The only thing that has changed is that I replace the alternator when I replaced the fan bracket. What can I check on this economy problem? thanks Mark Quote Link to comment Share on other sites More sharing options...
Jerry Bransford Posted September 22, 2007 Share Posted September 22, 2007 A bad 02 sensor is often the cause of suddenly reduced fuel economy. :) Quote Link to comment Share on other sites More sharing options...
Robert Young Posted September 23, 2007 Share Posted September 23, 2007 Check your battery, if you had to replace the alternator you may have killed the battery. If so, the alternator may be delivering full charge all the time and putting extra load on the engine, so loss of mpg. If you can get a current probe on the line to the battery, you should see high rate charge for a short time (no more than a few minutes) after starting the car. Alternative, take the battery to Autozone, the ones in So. Cal. typically have a bettery tester that you can use with hope that you will buy from them. If you need a new battery, I highly recommend the Optima type spiral wound design, its a bit more money but worth it. Quote Link to comment Share on other sites More sharing options...
1990LS400 Posted September 23, 2007 Share Posted September 23, 2007 Most complaints of worsening gas mileage seem to take place during periods of upward spikes in gas prices as we have had during the past several weeks. Are you sure you are not just paying more attention to your gas mileage now that you are paying more at the pump? The EPA rating on the 90 LS400 I drove for 13 1/2 years was 18 mpg city / 23 highway and the gas mileage I got was often less than that. I kept track of every drop of gas that went into the car in a log book and still do that for all our cars. Quote Link to comment Share on other sites More sharing options...
Vern Dias Posted September 23, 2007 Share Posted September 23, 2007 Did your gas recently acquire ethanol? On my 2004 LS430 using an ethenol mix (E-10, NOT E-85) reduces my fuel economy by 2-3 MPG, decreases power, and throttle responsiveness. I just returned from a 4000+ mile road trip, and found that gas that did not contain ethanol gave much better fuel economy, throttle responsiveness and acceleration. Vern Quote Link to comment Share on other sites More sharing options...
paulo57509 Posted September 23, 2007 Share Posted September 23, 2007 Did your gas recently acquire ethanol? On my 2004 LS430 using an ethenol mix (E-10, NOT E-85) reduces my fuel economy by 2-3 MPG, decreases power, and throttle responsiveness. I just returned from a 4000+ mile road trip, and found that gas that did not contain ethanol gave much better fuel economy, throttle responsiveness and acceleration. Vern +1 Try refilling at another station the next couple of times and check your mileage. Quote Link to comment Share on other sites More sharing options...
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