1990 civic wagon fuel economy

I recently blew a head gasket in my 1990 civic wagon, and after
replacing the gasket and re-machining the head, along with changing the
belts and adjusting the timing i'm back on the road.

the troubling thing is that my fuel economy was nothing special to
begin with (26mpg), but after the repairs it has dropped to 18mpg! any
ideas on what could be causing this and how to fix it?

thanks!
theo

 

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Does it lack power / sputter for the first few minutes until the engine
starts to warm up? If so, your timing belt is probably out one tooth.
Mileage will suffer. Did you change the PCV while you were under the
hood too?

'Curly'

 

Thanks for the quick reply. I didn't change the PCV valve, but the car
starts fine and gives power right away. I heard that perhaps the ECU
needs to be reset, but theoretically it should already be reset because
I had disconnected the battery. Although I didn't give the ECU an idle
learn; I went ahead and revved up to about 5000rpm to test whether the
engine would overheat or not.

Would it be possible the ECU was not reset or that I didn't "teach" it
properly? If I break the fuse when pulling out the hazard fuse will I
still be able to drive? Are there any risks to resetting the ECU?

What other possible causes are there for this poor fuel economy? from
26mpg to 18mpg is a huge drop that I'm not sure just a faulty ECU would
cause. With gas costing $1.02/litre here, I'm anxious to get back to at
least 26mpg if not better!

Theo

 

check for coolant leakage - look inside the radiator, not the expansion
bottle. that's probably why you lost your head gasket in the first
place. insufficient coolant means the ecu's getting the wrong signal
and goes "rich".

 

yeah but you have the right power does not mean you have the right
mileage.
Possibly after you replaced the head gasket, the engine requires more
gas
to generate the same power before the head gasket was replaced.