Help! Really crappy gas mileage!

[SearchingBearCub]

Hi,

I have a 1987 Honda Accord LXi 2DR Hatchback with 242,539 miles on the clock which gets horrible gas mileage, to the tune of about 80 or 90 miles per tank in town. (I'm not keen to test its highway mileage..)

When I bought it in October of '05, it ran reasonably well once warmed up (and still does.) It also passed a San Francisco smog check on its first try with room to spare. Once I saw the horrible mileage, I paid a mechanically inclined friend to give it a tune-up. This consisted of new spark plugs, plug wires, cap and rotor, and air filter. The valve cover gasket was also replaced to stem an oil leak. He also checked my timing belt and pronounced it to be in good shape.

Still, the bad mileage persists. The PGM-FI light comes on as a bulb test at startup and goes out, as expected. All gauges appear to read in their normal ranges, and I have no warning lights.

When the car is started, its idle is erratic until it warms up. It finally settles on about 1250 to 1300 for warm idle, in Park.

Also, I had a coolant bypass hose on the back of the engine replaced. While the air hose was off the intake, my mechanic friend told me that the IAC looked quite clean, and did not seem to be restricted in movement.

Lastly, the car still has plenty of power (I can beat a motorcycle from light to light, and squel the tires, if I choose to) so I'm not noticing a power loss. I'm also not feeling any hesitation.

Does anyone here have some possibilities for me to pursue?

[ICEMAN707]

bad gas mileage with no leaks or other obvious performance problems means you are running rich. your tailpipe should emit alot of black carbon, causing it to get dirty all the time.

is your car running cooler than normal? if so, your ECT (engine coolant temp) sensor is bad. running cool makes the ECU run in openloop mode dumping more fuel into the engine than normal.

it could also be your thermostat stuck open and letting coolant flow faster than normal keeping the engine cooler, good but not always a good thing since it causes the ECU to do the same thing i mentioned above.

last thing would be a bad O2 sensor. a bad O2 sensor also causes the ECU to do the same thing, making you run rich.

replace those three and your problem should be fixed. start with thermostat, that's the cheapest. followed by ECT sensor, then O2 sensor (most expensive). also don't forget to flush your cooling system and put new coolant it with 50/50 mix water - or just buy the premixed 50/50 one.

[shepherd79]

First simple thing to do is check ECU for any code.
https://www.3geez.com/forum/showthread.php?t=26342

[SearchingBearCub]

Thanks for the replies so far.

As I stated in my post, the PGM-FI light comes on only as a bulb check at startup, then it goes out. Wouldn't this mean that no codes are stored?

As far as I can tell, the car does warm up to the correct operating temperature. The temp guage rises to about 3/8 of the way up the guage within about 5 minutes from a cold start, and the engine cooling fan does eventually cycle on and off.

I also have a hot upper radiator hose after the temp gauge reaches the 3/8 mark, and interior heat is constant and even.

Do these observations rule anything out, or suggest other items for me to check?

Thanks...

[shepherd79]

I don't know what to tell you.
like i said. check your ecu after highway driving just in case. IN some cases, you won't see the EFI light come on. I would check it anyway.

[HostileJava]

What about the fuel pressure regulator, if that isn't dumping enough fuel coud it cause the same type of problem he's describing?

Lastly, the car still has plenty of power (I can beat a motorcycle from light to light

What? I doubt the motorcycle was trying.

[SearchingBearCub]

Ok, I checked the ECU. Pushed and leaned drivers seat all the way forward, managed to get my hand on the ignition key while looking at the little red light. Turned the key to II while watching the light, nothing. Waited until I heard the audible click that coincides with the PGM-FI system finishing its self-test, still no light.

Rubbed my finger inside the tailpipe to check for residue. There was very little. I do not notice any smoke from the exhaust, other than during cold start in the morning, which is normal as far as I know.

Also, how could the car have passed emissions on its first try if it is running rich, but not enough to set the light?

How can I diagnose the fuel pressure regulator?

Regarding beating a motorcycle, no he may not have been trying very hard. Nonetheless I only mentioned it to illustrate that I am not noticing a power loss.

What's next?