reading codes on 93 Civic 1.5

My 93 Civic runs, but not quite right. When under acceleration, the
engine starts to run roughly. When the car's speed catches up to the
gas pedal position, it starts to run smoothly again. Shifting into a
higher gear and pushing the gas pedal causes rough running again, until
the car finally reaches cruising speed. When faced with a slight
incline that requires pushing the gas pedal, the rough running returns.

It occurs to me that this seems like a manifold pressure problem because
it corresponds to the gas pedal/speed ratio. The check engine light is
not lit. I used to read codes on my 89 Accord by looking at the light
on the computer under the driver's seat, but I don't see a computer
under the seat in this car. I can't find anything that looks like a
scanner terminal, either.

This problem came on suddenly a couple of days ago when the weather went
from 60 to about 15 degrees in a few hours. We parked the car in warm
weather, and it no longer worked correctly in cold weather. Today it's
65 again, and it still isn't right.

By the way, I unplugged the MAP sensor and started the car, and it ran
like crap. So if the MAP sensor is bad, at least it's better than no
MAP sensor. The first thing I did was change the fuel filter. It
didn't fix the car, but it was due anyway.

The only other thing I can think of that might cause such a problem is
the oxygen sensor. Is there a way to check these components
individually, or do I just need to figure out how to read codes? The
engine light isn't on anyway, so what should I do if I don't get any codes?

Robert Reynolds wrote:
> My 93 Civic runs, but not quite right. When under acceleration, the
> engine starts to run roughly. When the car's speed catches up to the
> gas pedal position, it starts to run smoothly again. Shifting into a
> higher gear and pushing the gas pedal causes rough running again, until
> the car finally reaches cruising speed. When faced with a slight
> incline that requires pushing the gas pedal, the rough running returns.
>
> It occurs to me that this seems like a manifold pressure problem because
> it corresponds to the gas pedal/speed ratio. The check engine light is
> not lit. I used to read codes on my 89 Accord by looking at the light
> on the computer under the driver's seat, but I don't see a computer
> under the seat in this car. I can't find anything that looks like a
> scanner terminal, either.
>
> This problem came on suddenly a couple of days ago when the weather went
> from 60 to about 15 degrees in a few hours. We parked the car in warm
> weather, and it no longer worked correctly in cold weather. Today it's
> 65 again, and it still isn't right.
>
> By the way, I unplugged the MAP sensor and started the car, and it ran
> like crap. So if the MAP sensor is bad, at least it's better than no
> MAP sensor. The first thing I did was change the fuel filter. It
> didn't fix the car, but it was due anyway.
>
> The only other thing I can think of that might cause such a problem is
> the oxygen sensor. Is there a way to check these components
> individually, or do I just need to figure out how to read codes? The
> engine light isn't on anyway, so what should I do if I don't get any codes?

1. reconnect the map sensor.
2. check the ignition system - replace the plugs, leads and distributor
cap is they're old.
3. say whether this is an automatic - clogged egr systems can give
similar symptoms.

jim beam wrote:
> 1. reconnect the map sensor.

I did that immediately, of course.

> 2. check the ignition system - replace the plugs, leads and distributor
> cap is they're old.

I regapped the plugs and replaced the cap and rotor. Still have same
wires. Could bad spark plug wires cause such a sudden and intermittent
problem?

> 3. say whether this is an automatic - clogged egr systems can give
> similar symptoms.

Manual transmission.

Robert Reynolds wrote:
>
>
> jim beam wrote:
>> 1. reconnect the map sensor.
>
> I did that immediately, of course.
>
>> 2. check the ignition system - replace the plugs, leads and
>> distributor cap is they're old.
>
> I regapped the plugs and replaced the cap and rotor. Still have same
> wires. Could bad spark plug wires cause such a sudden and intermittent
> problem?

absolutely. and re-gapping is a waste of time - it doesn't address
electrical leakage as plugs age. ordinary plugs are only ~$2.50 each
[use only ngk or denso] - simply replace. use a quality plug like
iridium if you want best performance/economy - they're $10 each or less.


>
>> 3. say whether this is an automatic - clogged egr systems can give
>> similar symptoms.
>
> Manual transmission.

"Robert Reynolds" > wrote
> My 93 Civic runs, but not quite right. When under
> acceleration, the engine starts to run roughly. When the
> car's speed catches up to the gas pedal position, it
> starts to run smoothly again. Shifting into a higher gear
> and pushing the gas pedal causes rough running again,
> until the car finally reaches cruising speed. When faced
> with a slight incline that requires pushing the gas pedal,
> the rough running returns.
snip
> This problem came on suddenly a couple of days ago when
> the weather went from 60 to about 15 degrees in a few
> hours. We parked the car in warm weather, and it no
> longer worked correctly in cold weather. Today it's 65
> again, and it still isn't right.

After tuning up the car (as Jim said, new wires, plugs,
distributor cap and rotor, OEM only--they pay for
themselves--and check timing), next I'd consider replacing
the O2 sensor. Worst case this will be pre-emptive,
especially on a car this old. You can buy an OEM O2 sensor
for a lot less than what OEM online parts dealers want at
https://www.automedicsupply.com/ . I used the latter for a
new O2 sensor for my 91 Civic. Works great. The store
shipped quickly.

A bad O2 sensor will not necessarily set a code on the 93
Civic.

Suspect next a clogged catalytic converter. Then the
question is why it became clogged.

Make sure the cooling system is topped off, too.

Elle wrote:

> After tuning up the car (as Jim said, new wires, plugs,
> distributor cap and rotor, OEM only--they pay for
> themselves--and check timing), next I'd consider replacing
> the O2 sensor. Worst case this will be pre-emptive,
> especially on a car this old. You can buy an OEM O2 sensor
> for a lot less than what OEM online parts dealers want at
> https://www.automedicsupply.com/ . I used the latter for a
> new O2 sensor for my 91 Civic. Works great. The store
> shipped quickly.

Thanks for the tip. I'll look for my part there. It appears to be the
more economical one-wire type, so I'm not too scared to buy one.

That leaves just the new plugs and wires.


>
> A bad O2 sensor will not necessarily set a code on the 93
> Civic.

Thanks for the info. By the way, how do you read codes on this car? Do
you have to get a Honda-specific scanner? Where is the connector? If
you guys are right I won't need it this time, but I wouldn't mind knowing.

>
> Suspect next a clogged catalytic converter. Then the
> question is why it became clogged.
>
> Make sure the cooling system is topped off, too.

The coolant looked good at the last oil change about 3 weeks ago. I
noticed when I bought this car last summer that it didn't appear to have
a catalytic converter. But I just went out and looked again and I see
something vaguely converter-like just under the exhaust manifold in
front of the engine. Is that where they hid it, or is that something
else?

I'll go ahead and finish the tuneup tomorrow and let you know how it
runs after that.

Robert Reynolds wrote:
> My 93 Civic runs, but not quite right. When under acceleration, the
> engine starts to run roughly. When the car's speed catches up to the

<SNIP>

You may just have _one bad tank_ of gas. Do you run injector cleaner
through it seasonally? I almost ditched a car when it suddenly went bad
and I couldn't find the trouble. It was BAD GAS.

'Curly'

motsco_ wrote:
> Robert Reynolds wrote:
>> My 93 Civic runs, but not quite right. When under acceleration, the
>> engine starts to run roughly. When the car's speed catches up to the
>
> <SNIP>
>
> You may just have _one bad tank_ of gas. Do you run injector cleaner
> through it seasonally? I almost ditched a car when it suddenly went bad
> and I couldn't find the trouble. It was BAD GAS.
>
> 'Curly'


Yeah, I thought of that one, too. It was down to about a quarter tank
when it went bad, and I filled it up at a BP station, but no change.

"Robert Reynolds" > wrote
> Thanks for the info. By the way, how do you read codes on
> this car? Do you have to get a Honda-specific scanner?

I am pretty sure it's like my 91 Civic: Codes are read
directly at the ECU via blinking flashing lights. See
http://media.honda.co.uk/car/owner/m...sk301/6-74.pdf
for help. It's not difficult. No special scanner or other
tool is required.

The ECU is located under the front passenger footwell mat.

Elle wrote:
> "Robert Reynolds" > wrote
>> Thanks for the info. By the way, how do you read codes on
>> this car? Do you have to get a Honda-specific scanner?
>
> I am pretty sure it's like my 91 Civic: Codes are read
> directly at the ECU via blinking flashing lights. See
> http://media.honda.co.uk/car/owner/m...sk301/6-74.pdf
> for help. It's not difficult. No special scanner or other
> tool is required.
>
> The ECU is located under the front passenger footwell mat.
>
>

That's a funny place to put it.

I haven't bothered to get a shop manual for this car yet, because I've
never had any trouble with it. It's a great car. Everything is laid
out so conveniently I didn't even need to look at a book when I changed
the timing belt and water pump at 100,000 miles. It took me about an
hour. I really love this car.

Thanks for the info.