93 Honda Civic Mileage gone bad

id do a compression test and replace the O2 sensor if its the original
one. its due, and directly effects emissions. if its bad, the engine
could be running rich. is the tailpipe sooty? were the plugs black?
grey? tan?

a small factor could be tire pressure. another factor could be brakes
dragging. jack up each wheel and see if they spin freely.

 

id do a compression test and replace the O2 sensor if its the original
one. its due, and directly effects emissions. if its bad, the engine
could be running rich. is the tailpipe sooty? were the plugs black?
grey? tan?

a small factor could be tire pressure. another factor could be brakes
dragging. jack up each wheel and see if they spin freely.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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

 

| 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

 

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

 

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

 

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.

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

 

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.

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