91 civic stalls, decrease in mpg

I have a 91 civic dx. The past few months the car will either stall, or
jerk then lose almost all power. The check engine light comes on when
this happens. It happens only occasionally, but during all types of
driving ( highway, 35 mph, or even just staarting up). If i turn the
car off and turn it back on, it resets and the car is fine for awhile.
The other symptoms are the mileage went down from ~35mpg or better
every tank, to 27-28mpg on the last three tanks. The other thing is
when i got an emmisions test my mechanic said it didnt pass the HC at
first (234 reading w/ 220 limit). He let it warm up for half an hour,
then did it again and it passed.

Any suggestions would be helpful. Could it just be the o2 sensor or
something else simple?

 

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You've probably changed your timing belt at least twice by now, based on
age (we don't know your mileage), but have you adjusted your valves? Do
you have stinky exhaust once it warms up? Do your records show a new PCV
along the way?

 

Actually it only has 77k on it, so the timing belt is most likely the
original (I bought it with 43k). The exhaust doesnt smell unusually
bad.

As far as time to change the PCV, I think, well hope, that might me
premature. Does anyone know if cleaning it out is easy/practical?

 

The PCV is easy to get at on your car (I used to have one, DX sedan
anyway). I can't remember how much they cost, but probably no more than
$10-15. I think the 'nut' part of the valve was SAE and not metric
(non-original valve?) on my car.

An aquaintance who is fairly handy with tools/mechanics could adjust
your valves for you, but I'm guessing a shop will charge you at least an
hour of labor.

Do you know how old the distributor cap, rotor, spark plugs, and wires
are? These are all consumable, (to some degree) fairly cheap parts that
can affect how well your engine runs.

Mark

 

wrote in

With the car fully warm, squeeze the PCV valve hose shut with a pair of
pliers. If the idle changes or the valve clicks, the valve is fine.

The idle will change, then smooth out again as the ECU adjusts the air
mixture. If the idle does not change when the hose is pinched shut, the
valve is plugged. Either way, a blocked PCV valve is not your problem here.
A blocked PCV valve will not cause the sort of decrease in gas mileage that
you are experiencing.

You need to get the Check Engine light code. Pull the carpet back from the
passenger footwell until you see the ECU. Turn the ignition to ON (but not
to START), and count the sequence of long and/or short blinks from the
ECU's red LED. Report back here.

Right now I'm thinking a faulty thermostat or temp sensor, fooling the ECU
into thinking the engine is too cool, but I need the code to verify.

 

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If that's the case, you're living on borrowed time. I doubt a belt has
ever lasted FOURTEEN years . . . :-( Time is just as important as mileage.

'Curly'

 

An old or blocked PCV valve may very well cause a significant decrease in
gas mileage. But I'm doubtful the PCV valve is behind the stalling.

Even if it's not plugged, the PCV valve's parts wear over time. Change it
with an OEM one. It's not hard to do, like Chopface said. You can do the
test that Tegger describes above; you should also hold it for at least 30
seconds and listen for a "click" sound. If there's no click sound, then the
valve isn't working.

My 1991 Civic was getting poor gas mileage around spring 2003. The PCV
valve had never been replaced. I didn't know enough to do the tests above;
I just replaced it, for around $20 with a dealer one. The old (and
original) one was chock full of waxy buildup. My mileage shot up 10-20%. It
was very noticeable. Other reports on the net document that a
malfunctioning PCV valve most certainly may affect gas mileage. It messes
up the ECU's take on the engine's condition, and the computer sends a
signal that results in rich (=excessive fuel) fuel-air mixtures.

I now clean out my PCV valve every few months or so. It typically has a few
specks of gunk in it. And I do mean little specks--Q-tip pick-able. It
would take a long time for this to build up to anything that would block
it. I remove the valve completely about once a year and spray it with a
little WD-40, too.

Ya, really. Start there. Various online manuals describe this.

If it's the O2 sensor, the good news is that it's very cheap to replace on
the 1991 Civics. I have a 1991 Civic and replaced the O2 sensor last
summer, as a pre-emptive measure and because it was so cheap, around $45
total, using an online site that had OEM sensors.

And replace that timing belt!

 

I would start by replacing the oxygen sensor and performing a tune up.
Before you replace your o2 sensor, I recommend that you get a bottle of
SeaFoam Engine Cleaner. This product can be found at your local Napa
Auto Parts store or Carquest. Start off by removing your air intake
rubber tubing off from the throttle body assembly. Then open up the
bottle of seafoam engine cleaner and pour half of the contents into a
spray bottle. Mix the solution with 50 percent water and 50 percent
seafoam. Be sure to shake it very well. Now, begin by spraying the mist
into the throttle body inlet while manually keeping the engine's rpm
above 2500. You will notice that your exhaust pipe will be emitting
some white smoke. This is perfectly normal because the solution is
cleaning the internals of your engine and decarbonizing all of the
baked on carbon deposits. After you finish the bottle turn the engine
off and let it sit for 15 minutes. Go ahead now and take the car out
for a ride on the freeway and apply heavy throttle to remove all the
excess carbon. Next replace all 4 spark plugs and make sure to gap them
to 0.44 in. Replace your engine oil and filter along with a brand new
o2 sensor. If you perform all these steps correctly, you should notice
a difference immediately. I hope this helps.

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