Honda Car Forum

I have a 1988 Integra with about 150k miles. In between fillups on a
road trip this year the car was all of a sudden running rough at
idle. And, it stumbles slightly during initial acceleration. I also
noticed at least a 15% reduction in highway fuel economy, though at
highway speed the car still runs fairly smooth. All cylinders are
firing.

The engine light occasionally comes on now for a few seconds then back
off, usually at idle. Idle speed is normal, and I've actually
adjusted it up due to the rough idle. Since the trip I have replaced
the plugs, cap, rotor, and air filter. I have since checked the ECU
and it indicates code #1 (oxygen sensor). Now, what exactly is this
telling me about the sensor? Is it possible to get this code due to
other conditions if the sensor is in fact still good?

When changing the plugs I noticed that number 3 was unusually black
(carbon). After a couple weeks with the new plugs, number 3 is again
blacker than the others but still firing fine.

I've reset the ECU and waiting for the next occurence. Should I just
replace the oxygen sensor? Any other ideas?

shallowpool <shallowpool@yahoo.com> wrote in news:c0f7a6a2-a8c6-44f5-8962-
b7ebc02aeac2@z28g2000vbl.googlegroups.com:

> I have a 1988 Integra with about 150k miles. In between fillups on a
> road trip this year the car was all of a sudden running rough at
> idle. And, it stumbles slightly during initial acceleration. I also
> noticed at least a 15% reduction in highway fuel economy, though at
> highway speed the car still runs fairly smooth. All cylinders are
> firing.
>
> The engine light occasionally comes on now for a few seconds then back
> off, usually at idle. Idle speed is normal, and I've actually
> adjusted it up due to the rough idle.



Bad idea. A band-aid fix at best.


> Since the trip I have replaced
> the plugs, cap, rotor, and air filter. I have since checked the ECU
> and it indicates code #1 (oxygen sensor). Now, what exactly is this
> telling me about the sensor? Is it possible to get this code due to
> other conditions if the sensor is in fact still good?



These old OBD systems only set an oxygen sensor code if the sensor reports
an out-of-range signal (less than .1 or more than .9). This can occur if
the wiring/connector is corroded or frayed. The sensor only outputs a max
of .9 volt, so wiring/connector integrity is crucial.



>
> When changing the plugs I noticed that number 3 was unusually black
> (carbon). After a couple weeks with the new plugs, number 3 is again
> blacker than the others but still firing fine.



If only #3 is black, then you've got some sort of problem specific to that
cylinder. Replacing the oxygen sensor won't fix that. Time for a
compression test and for making sure the spark is actually and reliably
making it to the plug gap.

Do you have EGR?





--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/

On Aug 31, 8:31*pm, Tegger <inva...@invalid.inv> wrote:

> > The engine light occasionally comes on now for a few seconds then back
> > off, usually at idle. *Idle speed is normal, and I've actually
> > adjusted it up due to the rough idle.
>
> Bad idea. A band-aid fix at best.

This was just to keep the engine from dying at stop lights.

> These old OBD systems only set an oxygen sensor code if the sensor reports
> an out-of-range signal (less than .1 or more than .9). This can occur if
> the wiring/connector is corroded or frayed. The sensor only outputs a max
> of .9 volt, so wiring/connector integrity is crucial.

So, does this mean that the error code is telling me that the sensor
is indeed going bad? I wonder if it could be going bad on the rich
side, causing my poor fuel economy. I will try to put a volt meter on
it. The electrical coupling is indeed coated with leaky oil. I will
clean it up and see what that does.

> If only #3 is black, then you've got some sort of problem specific to that
> cylinder. Replacing the oxygen sensor won't fix that. Time for a
> compression test and for making sure the spark is actually and reliably
> making it to the plug gap.
>
> Do you have EGR?

There is no EGR as far as I can tell. No pipes to or from exhaust and
intake manifolds. Nothing that looks like a big EGR valve as shown in
your EGR photos. Only the oxygen sensor is attached to the exhaust
manifold.

I'll try a compression check, although the engine doesn't skip/chug as
I would expect it to with a bad cylinder. It just runs rough
consistently.

Thanks for the info.

> --
> Tegger
>
> The Unofficial Honda/Acura FAQwww.tegger.com/hondafaq/

shallowpool <shallowpool@yahoo.com> wrote in
news:80656309-adb5-4ca2-9894-37080c4c755c@q14g2000vbi.googlegroups.com:

> On Aug 31, 8:31*pm, Tegger <inva...@invalid.inv> wrote:
>
>> > The engine light occasionally comes on now for a few seconds then
>> > back off, usually at idle. *Idle speed is normal, and I've actually
>> > adjusted it up due to the rough idle.
>>
>> Bad idea. A band-aid fix at best.
>
> This was just to keep the engine from dying at stop lights.



Still a lousy idea.


>
>> These old OBD systems only set an oxygen sensor code if the sensor
>> reports an out-of-range signal (less than .1 or more than .9). This
>> can occur if the wiring/connector is corroded or frayed. The sensor
>> only outputs a max of .9 volt, so wiring/connector integrity is
>> crucial.
>
> So, does this mean that the error code is telling me that the sensor
> is indeed going bad?


No. It means the connection may (or may not) be poor. I have no idea if
you're using an OEM sensor or an aftermarket one, and I have no idea
what kind of electrical connection there exists between the sensor and
the ECU.



> I wonder if it could be going bad on the rich side, causing my poor
> fuel economy. I will try to put a volt meter on it.



Won't help. You need a Digital Storage Oscilloscope (DSO) to properly
diagnose an oxygen sensor.




> The electrical coupling is indeed coated with leaky oil.



Oops. Got a leaky valve cover gasket, evidently.



> I will clean it up and see what that does.



Better to find a good Honda-specific garage, scarce as those are...


--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/