I have an older-model Accord and am trying to diagnose a problem that other mechanics in my area have had trouble with.

My gas mileage is very bad in the city: 15 MPG. On the highway, I get mileage that's close to normal (27 MPG). After watching a few videos, I decided to investigate and noticed the smell of fuel coming from the exhaust pipe. I also looked for leaks by looking for fuel dripping from the bottom of the car to the ground while idling for about 3 minutes. I did not see any dripping. Third, I looked at the gas cap and there are no issues with the seal.

My theory is that the fuel is burning too rich and this condition is not being detected. Because the gas mileage improves at highway speeds, I believe that the mixture is not affected by speed and that a sensor may have malfunctioned, but I am not sure. Any help is appreciated. Thanks!

 

Is the Check Engine Light (CEL) illuminated? If yes, see DIY forum for how to extract codes (2-digits).

If no CEL, then fuel may be leaking into the engine, via leaking injector or ruptured fuel pressure regulator.

Fuel pressure regulator (FPR) is checked by removing vacuum reference line and sniffing. If you smell gas, the FPR diaphragm is ruptured and it must be replaced. FPR is on end of the injector fuel rail.

A leaking injector should drop a code 43 (Fuel Supply System). If not, then either injectors must be individually tested by fuel pressure drop test. A special tool is req'd which is fairly expensive. It would be simpler to pull and have the injectors rebuilt/replaced.

Finally, I would inspect for gas leaks on the fuel rail and underneath the car (rusted fuel lines).

good luck