My car MPG drop

91 civic automatic. 150,000 miles. my car is getting weird. I used to get
over 33 miles now I'm getting 22. I don't know why it drops. It happens
in a two week I did not drive while.

 

In the winter, I tend to get very poor mileage. Over 10 percent less
when compare to summer driving. I believe the reason for this
inconsistency is that engine takes much longer to reach optimum working
temperature and will run 'rich' until it completely warms up. As a
guest-estimate, I think it take about 10 minutes of continuous driving,
until the engine warm-up (or loosens-up) enough to return optimum
mileage. So, if most of the driving is short excursions, and he weather
is cold, expect very poor mileage.

Pars
98 Civic Hatch

 

How's your acceleration, like going from 30 mph to 65 mph as you enter a
highway? If poor compared to what you're used to, your car isn't getting the
power that's usual. Maybe a cylinder is misfiring.

Switch gas stations. See if there's improvement.

Replace spark plugs, spark plug wires, distributor rotor and distributor cap.
(Assuming this has not been done recently.)

Replace Positive Crankcase Ventilation (PCV) Valve. Have you ever done this?
It's a $20 part, tops. Replacing mine for the first time at around 140,000 miles
improved my fuel mileage 10 to 20% on my 1991 Honda Civic Standard Transmission.

Replace the fuel filter. Replace the air filter.

There are other possibilities. Look for other posts in the coming days.

 

PVC would be my first choice to check - a similar problem happened to me
last year on my Lebaron - dropped 1/3 the mpg, almost over night. Had
the PVC valve replaced and presto....

 

My 91 Civic HB developed the same problem but over a longer period of
time. Changed the O2 sensor and the milage came right back. Finally
retired it a few months ago... with 427,000 miles.

 

Thus spake Red Cloud on 11/25/2003 1:27 PM:

With a drop that bad, I'd suspect O2 sensor. My wife's POS Saturn
developed the same thing (granted about 100,000 earlier than yours), and
simply changing the O2 sensor brought it right back.

-moitz-

 

Thus spake Red Cloud on 11/25/2003 1:27 PM:

With a drop that bad, I'd suspect O2 sensor. My wife's POS Saturn
developed the same thing (granted about 100,000 earlier than yours), and
simply changing the O2 sensor brought it right back.

-moitz-