93 Honda Civic Mileage gone bad

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

Reply to
Danny Beardsley
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"Danny Beardsley" wrote in news: snipped-for-privacy@z14g2000cwz.googlegroups.com:

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.

Reply to
Jim Yanik

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.

Reply to
High Tech Misfit

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.

Reply to
jim beam

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.

Reply to
Danny Beardsley

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.

Reply to
Danny Beardsley

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.

Reply to
Danny Beardsley

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.

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has great prices for OEMoxygen 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:

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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.

"Danny Beardsley" wrote

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

Reply to
Elle

Low mileage => more gas or more work by engine for a given baseline hmm ...

I presume you have ruled out obvious driving changes such as altitude/distance/less hwy/more city/lead footing/avg speed etc...

is that automatic tranny ?

- have you noticed an increase in RPM per given cruising speed ? that is at

60 mph you used to be at say 2500 rpm now you are at 3000 rpm ?

- any chance your transmission is the problem maybe you lost 4th/5th gear ??

- if manual are you forgetting to shift into 5th ;)

- since a vtec any chance your engine stuck in vtec high rpm performance mode ? or something wrong with vtec system ?

- has the CHECK engine light come on or blinked recently ? considering VTEC function is controled electronically (ECM function) could be VTEC malfunction > you could try running self diagnostic and look for system error codes ? > maybe try reseting the ECM

i have '93 Civic Si same engine and have never really seen (> 31mpg)

maybe the VTEC was broken before and now it works ?

I usually get about 28-30 , maybe your foot is heavier now :)

using different grade oil (factory recommended) or any new additives ?

ah ha ! thought i had an idea

HTH

most of this was out of Factory Service Manual, a very good book if you like to work on the honda i do not know how chilton/hayes etc compare but the Honda Service manual seems very good

Reply to
Rob B

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.

dan

Reply to
dan

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

Reply to
Michael Pardee

I'd add an OEM thermostat to the list....

Mike

Reply to
Michael Pardee

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.

Reply to
SoCalMike

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.

Reply to
SoCalMike
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.

Reply to
Danny Beardsley

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.

Reply to
Danny Beardsley

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

Reply to
Danny Beardsley

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.

Reply to
Danny Beardsley

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.

Reply to
SoCalMike

| Consider a new oxygen sensor. Without checking its output 1st ? This is stupid, user can chk sensor's output easily.

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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

Reply to
TE Cheah

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