93 Honda Civic Mileage gone bad

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.

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!!!

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 }

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

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

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

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

"Danny Beardsley" wrote

appropriate

to work

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.

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

that the old

close all the way

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

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

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

I've never found a reliable way of testing them. I clean the bejeebers out of them with carb cleaner (some don't survive parts dip) if I don't have any place to buy a replacement at the time. They normally shouldn't close all the way, although they can close at wide open throttle or when you are holding it in your hand. At idle, they should allow some bypass to scavenge the small amount of blow-by. At cruise throttle, they should open to scavenge the increased amount of blow-by. Your old one may be defective - it sounds like the spring has become weak. Normally you should feel quite a bit of resistance (the proper direction, blowing from the engine end) at pressures we puny humans can produce.

Mike

Sadly, it's very possible. Honda spark coils are not very tolerant of being fired up without a load. My son zapped his coil just using the starter to "bump" the distributor to the proper position. The result can be seen at

D'oh! The initial problem sounds like a bad "main relay" - see for the straight scoop on that. Mike

oxygenated gas. used in many parts of california from (IIRC) nov thru march.

That is a classic pass/fail test for O2 sensors, but most sensors fail by becoming more and more sluggish - degrading over time. When new, they should produce over 7 transitions per second as the output drives the mixture back and forth past the ideal point. As the sensor ages, the response rate drops until the ECU will no longer tolerate it and you get the "check engine" light. As another recently reported here, replacing an old O2 sensor can improve throttle response even if the reaction time of the old one was not causing the ECU to complain. The ECU must also adjust the mixture at a rate that is independent of the condition of the O2 sensor (because it has no direct knowledge of the sensor's condition), so the mixture will fluctuate more in proportion to the sluggishness of the sensor.

IMHO the "sweet spot" in the car's life for replacing the O2 sensor is around the half-way mark, or between 100K and 150K miles. I doubt many O2 sensors last the life of good modern cars, so we can all expect to replace the sensor once (whether the little light comes on or not). If we are going to remove the sensor for testing because we suspect it, I suggest the best thing to do is put in a new one and be done with it.

Mike

"Michael Pardee" wrote in news:eqqdnVVSGs6I1wHenZ2dnUVZ snipped-for-privacy@sedona.net:

Question;use a OEM Honda/Acura O2 sensor,or will a 3rd party sensor suffice? (at a lower price)

Elle found a place to get OEM on-line at a nice price for early models. I thought I saved the link but maybe she'll see our plight and repost it.

Mike

You are right. The secondary coil shorted someplace and is now only half the resistance it should be.

I'll post the best price when I find it.