93 Honda Civic Mileage gone bad

"Danny Beardsley" > wrote in message
ups.com...
> 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.
>

maybe i misunderstand ...

you completely by passed the *EC* (electronic control) part of VTEC
variable valve timing and valve lift electronic control system

The mechanics of the VTEC engaging is hydraulic (oil pressure) via the VTEC
oil solenoid which performs as you describe *BUT* the control of the VTEC
engaging through VTEC solenoid is the ECM which is electronic and uses
several measures to control VTEC solenoid operation {rpm, load, temp,
speed }

> 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.
>

and engine would probably vibrate, seem unbalanced
i was thinking about VTEC solenoid or ECM control signal which would affect
all the cylinders

>
> Driving habits have not changed.
>
> Nope, Oil is 10w30, hasn't changed.
>
> I have the Factory Service Manual, it's pretty useful.
>

well my VTEC electronic info comes from page 5-9
"switchover from one VTEC profile to other is controlled electronically"

so i am just suggesting that one cause for using more gas (your %25 drop in
fuel economy) could be fault in the VTEC control, for instance if the VTEC
solenoid is stuck in high rpm mode all the time then you would be using more
gas, of course i suspect there would be some other symptoms like low rpm and
low end rough starting and rough idling, but once you get into 2500 rpms or
so it would just seem like great performance

I like the HO2S idea too but there should be some performance problems
there as well like rough idling or stumbling or some noticeable performance
problem associated with richened air mixture

"jim beam" > wrote in message
...
> 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.
>
>

that is what i am talking about, i wish i had read this before posting my
rebutal

> > 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.
>

non-activating may give better gas mileage ?

i was thinking constant-activation, either VTEC solenoid stuck in high rpm
mode, which i supppose effectively becomes manual oil pressure control (is
that a trick to get lower mid-range performance out of VTECs ?)

or the ECM signals causing VTEC engaging are maybe engaging high rpm mode a
bit lower than factory design specs. say engage VTEC at 2500-3000 rpm
instead of 4500

Sounds good; will do.

"Michael Pardee" > wrote
> I'd add an OEM thermostat to the list....
>
> Mike
>
> "Elle" > wrote

"Danny Beardsley" > wrote
> 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.

Do you mean you pinched shut its hose, and within about 30
seconds, you heard it click?

If so, I agree this test is an indication it /seems/ to work
correctly, but it's not conclusive. Its spring wears, for
one, allowing the click to occur, but not allowing proper
throttling.

I estimate my mileage improved 10% to 15% when I replaced
the PCV valve on my 91 Civic at 12 years and about 140k
miles. It was /very/ noticeable, since back then I reset the
trip odometer at fillups and would drive until the fuel tank
was near empty.

Seems like all the cheap fixes (including the O2 sensor)
have been covered. If these don't repair the problem, then
I'd be searching elsewhere.

Of note: Someone in the thread did mention that some parts
of the country switch to a much lower heating value of
gasoline sometime in the Fall, right? IIRC, that right there
will drop mileage on the order of 10%. Also, I don't know
where you are, but where I am, we're having unusually cold
temperatures. My mileage is taking a beating of about 5-10%
lower than it did last year at this time.

Rob B wrote:
> "jim beam" > wrote in message
> ...
>
>>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.
>>
>>
>
>
> that is what i am talking about, i wish i had read this before posting my
> rebutal
>
>
>>> 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.
>>
>
>
> non-activating may give better gas mileage ?
>
> i was thinking constant-activation, either VTEC solenoid stuck in high rpm
> mode, which i supppose effectively becomes manual oil pressure control (is
> that a trick to get lower mid-range performance out of VTECs ?)
>
> or the ECM signals causing VTEC engaging are maybe engaging high rpm mode a
> bit lower than factory design specs. say engage VTEC at 2500-3000 rpm
> instead of 4500
>
ecu's/ecm's do not get it wrong. they either work, or they don't. and
these honda ecu's/ecm's are spectacularly reliable.

of there /is/ a vtec problem, it's more likely solenoid or wiring.

Thanks guys for the VTEC info... I'd always wondered how oil pressure
was stable enough to engage something at a specific RPM. I guess I
better read the factory manual a bit closer. I'll find some way to
check the solenoid.

Thanks for the VTEC info... I'd always wondered how oil pressure alone
was stable enough to engage something at a specific RPM. I guess I
better read the factory manual a bit closer. I'll find some way to
check the solenoid.

I bought a new PCV, took the old one out and it turns out that the old
one works better than the new one(the new one doens't close all the way
and the flow is more restricted), it's just a one-way valve, that's it,
no wonder they are cheap.

So I left the old one in.

Update: Could be completely unrelated. The PO told me about this very
intermittent problem and this is only the second time I've run into it.

The car doens't start after it's been warmed up. It turns over
great... but just doesn't run. The previous time, It started after
several attempts (30 sec or so).

This time, I had warmed it up and then did a compression test. Then,
when going to start it again, it just won't run. I've checked the
usual stuff (sparks plugged in, injectors plugged in). I even tried
cranking for 20 seconds to see if the ECU would register something
faulty. Nothing. My guess is it will start after cooling down....
why though?

Could I have messed something up ignition wise by cranking with the
plug wires removed?

"Danny Beardsley" > wrote
> I bought a new PCV, took the old one out and it turns out
that the old
> one works better than the new one(the new one doens't
close all the way
> and the flow is more restricted),

How do you know this isn't the way it's supposed to work?

> it's just a one-way valve, that's it,

If you google on the internet and examine a cut-away, it's
far more than a check valve.

> no wonder they are cheap.
>
> So I left the old one in.

Suit yourself. :-) I saw your other post and see you're now
dealing with a bigger problem. I'd be checking the coil.