I have an 89 Civic wagon pristine condition, just broke 80k. D15b2 getting 20mpg city. Both ef sedans Ive had with the same engine and auto transmission got 26-28 city even when one had 225k on it. Cant figure out why the mileage is so terrible on this engine. Ive replaced....

Water pump
Timing belt
Plugs
Wires
Rotor
Cap
Throttle body assembly
Fuel filter

Last thing I can try that I can think of is injectors. Any thoughts?

 

bad oxygen sensor possibly. old ignitor/coil maybe.

 

Is your check engine light on?
Does the engine run awkward at any time?
Does the exhaust smoke?

Perform a compression check and lets see what your numbers are.

The O2 sensor could be on it's way out and is 'lazy'.
Injector cleaner can help clean up your injectors. I would start with that followed by a new fuel filter (after the tank of gas with the injector clean has finished) before throwing new ones in.

 

Tried an o2 sensor. At very rare occasions it shudders or hesitates at idle. Timing is perfect. Also its been throwing a vss code 17 for the past several months at least. If theres a wire broken at the gauges for the vss signal would that throw off the computer resulting in terrible gas mileage?

 

Does your speedometer work?
The stock speed pulser is mounted on the back of the speedometer.
If the cable drive from the transmission is disconnected or broken, then the speedometer doesn't work and same with the speed pulser.

Very unlikely that your wire from the pulser to the ECU is damaged unless you have been doing some wire cutting in your dash.

 

Yep, speedometer works fine.

 

You get to pull your cluster out and check the wire from the pulser to ECU.
If it checks out to be fine, then replacing the pulser (or simply replace the entire cluster).

 

That's what I had planned. No one ever answered whether this explains the gas mileage or not.

 

It can definitely effect your gas mileage.