My 1994 Lexus has a rather sudden and dramatic drop in MPG.

Asked by Oldlexus Mar 14, 2013 at 11:00 AM about the 1994 Lexus LS 400 RWD

Question type: Maintenance & Repair

I've had this car for 9 years, and during this time I've always gotten 19 to 20 miles per gallon. In recent months it dropped to 14 MPG and was running rough. My driving habits have not changed at all. I've had the following work done:
Full tune up ($800)
Replaced 02 sensor
Replaced mass flow meter
Replaced timing belt and water pump
Since then, my MPG has actually gotten WORSE. It's down to about 10 MPG.
It has 158,000 miles on it and has been a great car. One thing I notice is that when I start it up in the morning, there is a very strong smell of gas around the car.
Fuel pump? Thermostat problem? Any ideas? I love this car but am running out of money to put into it.

2 Answers
177,545

tenspeed answered 11 years ago

Gas smell would point to a fuel problem. Have the fuel regulator checked. The regulator has a diaphragm. The engine vacuum pulls on it and the excess pressure is sent back to the tank. If the diaphragm ruptures, raw gas is sent into the air intake and fuel pressure at the injector nozzle increases. Both conditions result in a very rich mixture and decreased MPG's. --- Usually on a older vehicle the O2 sensor response slows down and signals more fuel than necessary at the injectors. Since you replaced the O2 sensor, that can't be it. -- I repeat, have it checked and tested before replacing to make sure it is the cause.

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