Lower gas milage after timing belt change

I just had the the 3rd timing belt replacement on my 94 Accord LX and
noticed about 10-15 % lower gas milage after it though the car runs
smooth. I estimated this by noticing how many miles I could drive from a
full tank till the guage touches the Empty mark. It used to be around
330 miles, now it's around 290.

First I thought this might be due to perhaps a different, less efficient
gasoline mix they are selling during the winter season in my state, but
when I heard a Accord Ex owner on a local auto show calling in with
virtually the identical issue (lower milage after a timing belt change)
I started wondering if this is something more common. I's strange
because, if anything, I would expect a better milage after such a major
maintenance that includes a tune-up as well. The radio show host did not
really have a good answer and I wonder if any of you have heard about
this issue before.

KJ

 

The only way this could happen is if a mistake was made.

Either something's not been reconnected properly, or the belt is off by a
tooth. I vote for the second reason. Go back and get the garage to check
the alignment again.

 

Oh, not that! It would be a big job. What if the tune-up was not done
right? Couldn't that also cause such a drop in milage?

KJ

 

"tune up"? with computerized ignition and injection, it's not like
you're going to minutely adjust the dwell or the mixture here dude. the
only reason you get big disparities is because of big screw-ups. i'm
with tegger - check the cam timing.

 

Sure would! And that's the garage's problem, not yours. They have an
obligation to perform the servicing correctly, and to fix it if it wasn't.

That's what I meant by something "not reconnected properly". Suppose they
damaged a sensor or something? Or hooked up a vacuum line in the wrong
place?

Besides investigating the strong possibility the belt alignment is off,
they need to do a thorough check to make sure no other mistakes were made.

 

Don't guess, measure. How many miles do you go between fill ups and
how many gallons does one take? Do this over several tanks.

 

An other than competent mechanic could easily put the timing belt on
one-tooth off. Have a talk with the manager/owner. What exactly was
done with the tuneup? Changed spark plugs? Valve adjustment?

 

you think driving a thousand miles on a mis-timed cam is a good idea?

 

That's my intention. I only drove 2-3 tanks of gas since the timing belt
change and figured the fewer miles driven per tank was due to colder
weather till I heard that other guy call in the car talk show with
similar observation. Now I am getting concerned. But because the engine
otherwise seems to run smoothly and without loss of power, I figure I
can afford to drive a couple more tankful before I talk to the shop
again so I don't look like a fool in case I am wrong.

KJ

 

Both.

KJ

 

If one of the cams was off by a tooth, you'd have a definite, and
objectionable, change in engine behavior from what you're used to.

If the engine behaves /exactly/ as it did before the service, then I would
advise attempting to more precisely determine what your mileage actually is
before panicking.

 

Following your suggestions I did measure the mileage and fuel
consumption after three fillups and I got surprisingly good fuel economy
that was consistently between 25.5 and 25.8 MPG. This is for combined
mileage for about 50-50 city (suburban) and freeway driving without
using A/C. I can hardly believe it because this is better than even the
old (higher) EPA estimate for this A/T model. Now I wonder how much was
the MPG *before* this timing belt change. Strange, but I'm not
complaining any more.

KJ

 

Well there you go.

I've long contended that most people have no real idea of their car's fuel
consumption, regardless of what they claim to be getting.

 

Well, that's why we keep coming to Tegger for answers. ;-) But
seriously, it appears that when the fuel guage needle is close to the E
mark, it is a pretty unreliable indication of how much fuel is still
left in the tank. That mark can also quickly change a notch after quick
braking episode. So I think that's where my mistaken perception was
coming from.

KJ