Hi,

I have a '99 Accord 2.3 liter 5 speed, 120k. Until last fall, I was getting about 33mpg in driving that was about 4/5ths country roads, 45mph with few stops, and in-town for the rest. Suddenly, like within a period of a couple of weeks to a month, last october, mileage dropped to around 29.

I keep tire pressure at around 35. Air cleaner was less than 6 months old. I don't think there are alignment issues--tire wear is even. Car was tuned (new plugs, wires, I think injectors were cleaned, I forget what else) right after the drop, may have kicked mileage up half a mpg to 1 mpg. Fuel filter may be original (I got the car at 67k) but Honda dealer tells me it's good for 150-175k. The guy who tuned the car suggested ethanol, which had just started being added to the gasoline for the winter (for the first time here) might be the culprit, but Mass has only 5% etoh, so my estimate is that might account for 1.5mpg (roughly 5% of my gas mileage) drop but no more.

Any ideas?

Thanks,

David

 

the change in weather might have some affect on gas mileage drop ..colder weather, engine runs more on fast idle when warming up,,,, winter fuel ?

 

Winter fuel is what I was thinking too, but if he bought it at 67k, he should have seen a winter before. The fuel filter seems questionable. 150-175k? How do you know when its bad? Bad fuel economy?

 

It wasn't the cold weather. I had very little drop the previous winter, maybe a mpg at most.

 

If you haven't replaced ignition parts recently, I would start w/ new spark plugs. A good set of iridium plugs can make a world of difference. Also primary O2 sensor (forward of catalytic converter) can gradually reduce performance w/o setting a code. I have an Acura 2.5TL that I thought was running pretty fair. Under a Acura recall program, the wires, plugs, distributor cap, rotor, and O2 sensor were replaced. I was amazed at difference in idle smoothness and fuel efficiency increased modestly 5-10% perhaps.

Air intake filter should be replaced. Make sure PCV and PCV hose are clean and working.

Check fuel pressure regulator vacuum reference line for smell of gasoline. If the diaphragm fails, gasoline is pulled into the engine through the vacuum reference line and fuel efficiency suffers substantially. New regulator is necessary if you smell fuel.

good luck