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1991 Honda Accord 4cyl : MPG has dropped

I was getting great mileage on my 1991 Honda accord (190K). It’s down to 23mpg (combined hwy/city). Feels like there’s some power loss. Mechanics have checked the computer codes, oxygen sensor, air filter. Put in new spark plugs, no excess oil burning, 4 brand new tires at proper inflation.

Thanks in advance.

What about fuel filter? Check for exhaust blockage? Check of fuel pressure? Dragging brakes?

Check the coolant temperature sensor.

Down to 23 combined? What was it before? Is this a drastic reduction in MPG. To be honest 23 combined on a 20 yr old 200k motor doesn’t sound that bad at all. I only get 24 at best on a '99 Camry with only 65k.

I was told the fuel filter, and fuel pressure is fine and any issue with it won’t cause MPG loss. Another mechanic just told me that the OBD1 computer codes won’t necessarily show a lazy oxygen sensor so, maybe that is the problem. The brakes are not dragging. I used to get over 30mpg on highway.

My 91 Camry V6 went from 23 down to 19 mpg. I replaced the oxygen sensor and it immediately went back to 23. It was only with cold temps (below 32) that the check engine light came on and gave the bad oxygen sensor code. I think you’re on the right track.

According to the revised EPA estimates if you have an automatic, then your car should get 19 MPG City and 26 highway for an overall 22 MPG combined. If you have a manual, then it’s rated for 21 city and 27 highway, with 23 MPG being the combined score. If you are getting 23 MPG overall, you are getting exactly the kind of mileage that your car is rated for. There’s likely nothing wrong with your car.

Thanks for all of the fast responses! Yes, I was told about the revised MPG and so while I guess it’s accurate, it doesn’t explain why the sudden drop in MPG. Maybe I’ve been spoiled somehow. The fuel gauge needle used to never move. I could get 400miles (hwy) on a tank. I will try the oxygen sensor when I have a bit of cash.

Fuel delivery problems can impact mileage, but if its been checked then its been checked.

Pursue the O2 sensor if it seems to make sense.

But also check the coolant temp sensor.

As for the idea that you should be getting 23 combined, it always amazes me that people pull out EPA estimates to tell others who’ve noticed a change that their mpg is actually “normal.” I have to assume that you have owned this car for a while and know it. I easily notice unusual changes in my own mpg just from knowing the car. If it has changed then there is a reason.

Based on experience with my '88 Accord here are some more possibilities in a 20 y.o. Honda:
Sticky thermostat (I change every 5-6 years)
Worn out distributor loses timing precision.
Wheel alignment can increase drag.

OK which mileage are we actually talking about? In the original post you used combined city/hwy, and in all your replies you state hwy mileage. I am confused. Like I asked before how much did your city/hwy drop?