93 Honda Civic Mileage gone bad

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I recently started getting very low milage in my 1993 Civic EX (1.6 L SOHC VTEC).
Previously I've seen between 32 and 38 (34 AVG.)
Now I'm getting about 25 MPG (it has steadily declined the last three
tanks).
Things I have checked/replaced: * Replaced Plugs and gapped them properly (The old ones looked fine) * Checked throttle body (no build-up) * Checked PCV valve: When I squeezed the tube going to the PCV, the idle went up, I guess that means it's open * Checked EAVC valve: I removed it and examined it, cleaned it and tested it. It checks out, the intake port was a little clogged and it was a little oily inside, but it tests fine (opens with a voltage). * Timing: It's pretty rock solid, though it's hard to get an actual reading cause the "pointer" or "indicator" is so far away from the pulley with the marks. * Haven't done a Compression Test yet * Fuel injectors: I was grabbing them with the engine running and could feel the clicking of the valve in only three of them. I removed the odd one and tested it and it seemed to work fine and fast when supplied with a few volts. *The air filter is super clean *Oil + Filter was replaced recently (1500 miles) *Performance seems top-notch, as fast as ever. *Valves: I just adjusted them and they weren't hardly off at all, only the valves on one cylinder were .001" too tight.
Note: About a thousand miles before the low milage, I jump-started the car and had noticeable engine shake after that. Recently, I replaced one of the motor mounts cause it was busted all the way through. Wierd, but this didn't really help much. It could be just that the new mount isn't as stiff as the old one was, or there are more busted mounts.
So, any ideas about the milage?
Thanks in Advance
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How's your catalytic converter/exhaust system? Maybe you're getting some restriction.Also,cold weather will cause a decrease in mileage.
Check your tire pressures,too.
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Jim Yanik
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I have not checked the catalytic converter, I'm not sure how to go about checking it except looking for holes. The sound of the car hasn't really changed.
It's not cause of winter, I've driven in the cold before and haven't got milage like this.
Tire pressures are correct. 30 PSI.
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Restricted cats show up mostly as the last bit of throttle not doing anything, or even making the engine stumble and surge at full throttle. The Haynes manual for the '90 to '93 Accord has a slick diagnostic for restricted exhaust systems using a manifold vacuum guage. It has you connect the guage and note the idle manifold reading. Then open the throttle so the engine is revving about 2000 rpm for a few seconds, and watch the guage as you release the throttle. If the reading returns to the original idle pressure within 2 seconds, the exhaust system is unrestricted. If the reading hovers near the 2000 rpm reading before dropping or if it slowly returns to normal the exhaust is restricted... could be the muffler or cat.
Mike
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Danny Beardsley wrote:

I could have sworn I answered this for somebody else today. :-)
Anyway, on to the questions.
Is this 25mpg city, highway, or mixed?
Are the new plugs OEM? What about the cap, rotor, wires? How are they?
What are your tire pressures? Are they the right size?
Are you a lead foot driver?
If you are in a part of the world where winter is settling in, that will decrease your mileage.
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Mixed
I didn't get the OEM plugs, but I just replaced the plugs today, Old: NGK's New: Bosch
Cap, rotor, wires, and coil were all replaced 30 or 40K miles ago.
Tires: 30 psi. Yes, they are the right size
No, I'm not a lead foot, The milage changed, my driving habits haven't.
Winter, yes but it doesn't get that cold here (Central California) and I've driven in colder weather and still had great milage.
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Danny Beardsley wrote:

ok, please clarify that point: are the timing marks correctly aligned or not? the pointer & the pulley marks need to line up under the timing light. if the timing belt's skipped, the "so far away" will be your problem - and indication of belt skippage. you don't state mileage. presumably the belt /has/ been replaced at some point. my experience is that some shops are not practiced at getting belt tension just right.

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I don't know why it is this way... but. The little plastic indicator on the timing belt cover is 3 or 4 inches away from the edge pulley having the marks. Because of this, it makes it hard to see if the marks on the pulley are lined up with the indicator correctly. What I should do is scratch a line from the indicator toward the center of the pulley. I haven't yet because it's super tight in there.
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That's quite a drop. How many miles are on your car?
IMO, you need a complete shotgun approach. You're halfway there. In order, this is what I'd do:
Check the coolant levels. Purge the cooling system of air.
I'd replace the PCV valve, assuming it's the original one.
Is the fuel filter due for replacement? If so, replace it.
I would be tempted to pull off the ignition wire of the suspect cylinder (with the suspect fuel injector) and see if engine power sounds like it goes down, as it should. OTOH, if you say performance is otherwise fine, then all four cylinders must be firing.
Consider a new oxygen sensor. https://www.automedicsupply.com/ has great prices for OEM oxygen sensors.
Stick with NGK plugs in the future. OEM plugs seem to be the consensus here.
Are cap, rotor, and wires OEM?
My site reinforces a few of these points: http://home.earthlink.net/~honda.lioness/id11.html
Elle Original owner, 1991 Civic (1.5 liter, manual transmission), 172k miles, 40+ mpg most of the year; about 39 mpg this time of year.

Civic EX (1.6 L

last three

looked fine)

PCV, the

cleaned it and

clogged and it

voltage).
an actual

from the

running and

them. I removed

fast when

at all, only

jump-started the

I replaced

through.
that the new

busted
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I'd add an OEM thermostat to the list....
Mike
wrote

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Sounds good; will do.

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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.
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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.
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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.
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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.
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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
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Elle wrote:

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

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