93 Honda Civic Mileage gone bad

dan wrote:
> Doesn't matter how you drive it. You should still be getting better mpg's.
>
> I second elle's opinion about the oxy sensor(s). The engine computer no
> longer gets realistic data from the oxy sensor and is running in default
> mode.

id third that. its pre OBD2, so it isnt going to throw a code. if you
have 2 sensors, id replace the one *before* the catalytic converter.

on my 98, it went and threw a code. it also ran like crap/stalled at idle.

200K miles.

Coolant is fine, new thermostat, the engine runs at the appropriate
temp.

I'll replace the PCV because they are cheap, but it seems to work
correctly.

I'm sure the fuel filter could use replacement, but I highly doubt this
is the problem.

I've done the test on the suspect cylinder and it has the same affect
the rest of the cylinders have when I remove the spark wire or fuel
injector wire.

Oxy sensor sounds possible.. I'll see if there are any testing
procedures in the factory manual.

The PO replaced the ignition stuff, I'll have to check the reciepts.

Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
by oil pressure. RPMs go up = more pressure. at a certain point, the
pins slide in and the intake valves use a different cam lobe. I
checked when I adjusted the valves, they weren't stuck. But I doubt one
VTEC being stuck on one cylinder would change the mileage this much.


Driving habits have not changed.

Nope, Oil is 10w30, hasn't changed.

I have the Factory Service Manual, it's pretty useful.

Sounds resonable, but then the Check engine light would be lit if the
sensor were failing... Well, "should" be it.

The old plugs were perfect and all the same.

Tires are properly inflated, brakes are not dragging. I also just
replaced the front rotors and pads.

Danny Beardsley wrote:
> Sounds resonable, but then the Check engine light would be lit if the
> sensor were failing... Well, "should" be it.
>
i dont think itll light up the check engine lamp on a pre-96/OBD2 car.
might not even throw a code. but the O2 sensor definately has an effect
on the mileage, and by 200k miles with the original sensor, its time to
replace.

| Consider a new oxygen sensor.
Without checking its output 1st ? This is stupid, user can chk sensor's
output easily. http://home.flash.net/~lorint/lorin/fuel/lambda.htm
If voltage is unstable, injectors are likely clogged.

| > any ideas about the milage?
chk car's minimum toe force needed ; tyres' toe-in may have increased
with usage, present tyres may have higher rolling resistance

"Danny Beardsley" > wrote in message
oups.com...
> The old plugs were perfect and all the same.
>
> Tires are properly inflated, brakes are not dragging. I also just
> replaced the front rotors and pads.
>
Did you readjust the parking brake? In one of the Prius groups a member was
complaining the mileage dropped about 10-20% after the most recent service,
and another suggested the parking brake had been adjusted too tight. Bingo!
(I am also assuming the slide pins were lubed during the brake work. Once I
overlooked that bit and received one of life's little lessons.) If you have
verified the brakes are not dragging, the parking brake isn't it... but the
lubrication state still could be.

Mike

Danny Beardsley wrote:
> Manual tranny. VTEC is *not* electronic, it is controlled PER cylinder
> by oil pressure. RPMs go up = more pressure. at a certain point, the
> pins slide in and the intake valves use a different cam lobe.

the vtec /is/ applied by oil pressure, but the oil is "switched" on and
off from the oil channel by an electrical solenoid. that is in turn
controlled by the ecu. simple oil pressure control is subject to too
many variables to be reliable.

> I
> checked when I adjusted the valves, they weren't stuck. But I doubt one
> VTEC being stuck on one cylinder would change the mileage this much.
>
>
> Driving habits have not changed.
>
> Nope, Oil is 10w30, hasn't changed.
>
> I have the Factory Service Manual, it's pretty useful.
>

non-activating vtec is /most/ unlikely to be the cause of declining gas
mileage.

Michael Pardee wrote:
> "Danny Beardsley" > wrote in message
> oups.com...
>
>>The old plugs were perfect and all the same.
>>
>>Tires are properly inflated, brakes are not dragging. I also just
>>replaced the front rotors and pads.
>>
>
> Did you readjust the parking brake? In one of the Prius groups a member was
> complaining the mileage dropped about 10-20% after the most recent service,
> and another suggested the parking brake had been adjusted too tight. Bingo!
> (I am also assuming the slide pins were lubed during the brake work. Once I
> overlooked that bit and received one of life's little lessons.) If you have
> verified the brakes are not dragging, the parking brake isn't it... but the
> lubrication state still could be.
>
> Mike
>
>
parking brake is self adjusting. should not be affected by servicing
the front! but it's a good thought - check the brakes - especially as
decreased gas mileage seems to coincide with recent brake service!!!