91 Civic EACV questions/diagnosis

I have been having some idling problems and decided to check out the
EACV system on my 91 Civic HB. No ECU codes, car starts fine. The main
symptom was the drop in idle speed to 500rpm when the engine was cold
and I was braking. Symptom went away after the car warmed up.
Following the troubleshooting chart in my Helm's manual, I proceeded
as follows:
1- Checked the resistance across the terminals of the EACV. Got
12ohms, within spec.
2- No continuity between each terminal and body ground - as expected.
3- Valve click when battery voltage is applied across the terminals.
4- Turned the ignition on, checked the voltage across the connector.
There is 12V - not expected according to the manual since the ECU
should be suppling the ground when EACV is activated. Confirmed by
disconnecting the ECU harness that indeed ECU is suppling the ground.

Put in another ECU - still voltage at EACV when ignition is on.
Put in another EACV - same problem with idle
New vacuum lines, bled the coolant - same problem with idle.

Question: Is it true that there shouldn't be ground supplied to the
EACV while the car is not running? The car was cold when I did these
tests so is it possible that ECU checks the coolant temperature and
decides to engage the EACV even if the car is not running?

Any ideas?

wrote in news:1179334791.067001.48930
@l77g2000hsb.googlegroups.com:

> I have been having some idling problems and decided to check out the
> EACV system on my 91 Civic HB.



Port FI or throttle body FI?



--
Tegger

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

On May 16, 11:38 am, Tegger > wrote:
> wrote in news:1179334791.067001.48930
> @l77g2000hsb.googlegroups.com:
>
> > I have been having some idling problems and decided to check out the
> > EACV system on my 91 Civic HB.
>
> Port FI or throttle body FI?
>
> --
> Tegger
>
> The Unofficial Honda/Acura FAQwww.tegger.com/hondafaq/

Stock D15B1 with throttle FI.

Sean > wrote in news:1179443290.449684.209930
@p77g2000hsh.googlegroups.com:

> On May 16, 11:38 am, Tegger > wrote:
>> wrote in news:1179334791.067001.48930
>> @l77g2000hsb.googlegroups.com:
>>
>> > I have been having some idling problems and decided to check out the
>> > EACV system on my 91 Civic HB.
>>
>> Port FI or throttle body FI?
>>
>>
>
> Stock D15B1 with throttle FI.
>
>


Do you have a Fast Idle Thermo Valve? This item boosts air feed during cold
running. If it sticks shut, cold idle speed will suffer.

--
Tegger

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

On May 17, 6:03 pm, Tegger > wrote:
> Sean > wrote in news:1179443290.449684.209930
> @p77g2000hsh.googlegroups.com:
>
> > On May 16, 11:38 am, Tegger > wrote:
> >> wrote in news:1179334791.067001.48930
> >> @l77g2000hsb.googlegroups.com:
>
> >> > I have been having some idling problems and decided to check out the
> >> > EACV system on my 91 Civic HB.
>
> >> Port FI or throttle body FI?
>
> > Stock D15B1 with throttle FI.
>
> Do you have a Fast Idle Thermo Valve? This item boosts air feed during cold
> running. If it sticks shut, cold idle speed will suffer.
>
> --
> Tegger
>
> The Unofficial Honda/Acura FAQwww.tegger.com/hondafaq/

No just the EACV.

wrote:
> I have been having some idling problems and decided to check out the
> EACV system on my 91 Civic HB. No ECU codes, car starts fine. The main
> symptom was the drop in idle speed to 500rpm when the engine was cold
> and I was braking. Symptom went away after the car warmed up.
> Following the troubleshooting chart in my Helm's manual, I proceeded
> as follows:
> 1- Checked the resistance across the terminals of the EACV. Got
> 12ohms, within spec.
> 2- No continuity between each terminal and body ground - as expected.
> 3- Valve click when battery voltage is applied across the terminals.
> 4- Turned the ignition on, checked the voltage across the connector.
> There is 12V - not expected according to the manual since the ECU
> should be suppling the ground when EACV is activated. Confirmed by
> disconnecting the ECU harness that indeed ECU is suppling the ground.
>
> Put in another ECU - still voltage at EACV when ignition is on.
> Put in another EACV - same problem with idle
> New vacuum lines, bled the coolant - same problem with idle.
>
> Question: Is it true that there shouldn't be ground supplied to the
> EACV while the car is not running? The car was cold when I did these
> tests so is it possible that ECU checks the coolant temperature and
> decides to engage the EACV even if the car is not running?
>
> Any ideas?
>
the eacv has to be set to an airflow level where the car will start,
hence activation voltage before the motor is running.

regarding symptoms, eliminate all other problems - this includes the
ignition system, plugs, ignition timing, etc. then go back to basics on
setting the warm idle properly. report back.

Sean > wrote in
oups.com:

> On May 17, 6:03 pm, Tegger > wrote:
>> Sean > wrote in news:1179443290.449684.209930
>> @p77g2000hsh.googlegroups.com:
>>
>> > On May 16, 11:38 am, Tegger > wrote:
>> >> wrote in news:1179334791.067001.48930
>> >> @l77g2000hsb.googlegroups.com:
>>
>> >> > I have been having some idling problems and decided to check out
>> >> > the EACV system on my 91 Civic HB.
>>
>> >> Port FI or throttle body FI?
>>
>> > Stock D15B1 with throttle FI.
>>
>> Do you have a Fast Idle Thermo Valve? This item boosts air feed
>> during cold running. If it sticks shut, cold idle speed will suffer.
>>
>
> No just the EACV.
>
>

You sure? Older Hondas had many secondary air inputs for cold running.

--
Tegger

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

On May 18, 6:08 pm, Tegger > wrote:
> Sean > wrote groups.com:
>
>
>
>
>
> > On May 17, 6:03 pm, Tegger > wrote:
> >> Sean > wrote in news:1179443290.449684.209930
> >> @p77g2000hsh.googlegroups.com:
>
> >> > On May 16, 11:38 am, Tegger > wrote:
> >> >> wrote in news:1179334791.067001.48930
> >> >> @l77g2000hsb.googlegroups.com:
>
> >> >> > I have been having some idling problems and decided to check out
> >> >> > the EACV system on my 91 Civic HB.
>
> >> >> Port FI or throttle body FI?
>
> >> > Stock D15B1 with throttle FI.
>
> >> Do you have a Fast Idle Thermo Valve? This item boosts air feed
> >> during cold running. If it sticks shut, cold idle speed will suffer.
>
> > No just the EACV.
>
> You sure? Older Hondas had many secondary air inputs for cold running.
>
> --
> Tegger
>
> The Unofficial Honda/Acura FAQwww.tegger.com/hondafaq/- Hide quoted text -
>
> - Show quoted text -

That is right, Si version has the Fast Idle Control Valve in
additional. My car is the base version, so just the EACV.

On May 18, 3:54 pm, jim beam > wrote:
> wrote:
> > I have been having some idling problems and decided to check out the
> > EACV system on my 91 Civic HB. No ECU codes, car starts fine. The main
> > symptom was the drop in idle speed to 500rpm when the engine was cold
> > and I was braking. Symptom went away after the car warmed up.
> > Following the troubleshooting chart in my Helm's manual, I proceeded
> > as follows:
> > 1- Checked the resistance across the terminals of the EACV. Got
> > 12ohms, within spec.
> > 2- No continuity between each terminal and body ground - as expected.
> > 3- Valve click when battery voltage is applied across the terminals.
> > 4- Turned the ignition on, checked the voltage across the connector.
> > There is 12V - not expected according to the manual since the ECU
> > should be suppling the ground when EACV is activated. Confirmed by
> > disconnecting the ECU harness that indeed ECU is suppling the ground.
>
> > Put in another ECU - still voltage at EACV when ignition is on.
> > Put in another EACV - same problem with idle
> > New vacuum lines, bled the coolant - same problem with idle.
>
> > Question: Is it true that there shouldn't be ground supplied to the
> > EACV while the car is not running? The car was cold when I did these
> > tests so is it possible that ECU checks the coolant temperature and
> > decides to engage the EACV even if the car is not running?
>
> > Any ideas?
>
> the eacv has to be set to an airflow level where the car will start,
> hence activation voltage before the motor is running.
>
> regarding symptoms, eliminate all other problems - this includes the
> ignition system, plugs, ignition timing, etc. then go back to basics on
> setting the warm idle properly. report back.- Hide quoted text -
>
> - Show quoted text -

That makes sense that EACV is open at start up but I don't understand
why it is conflicting with the service manual troubleshooting chart.
General question: When are the output signals calculated by the ECU?
Whenever the ignition is on or whenever the car is running?
As for the other items. The only thing I haven't checked so far is the
ignition timing and I am planning on doing next week after I change my
timing belt.

Sean wrote:
> On May 18, 3:54 pm, jim beam > wrote:
>> wrote:
>>> I have been having some idling problems and decided to check out the
>>> EACV system on my 91 Civic HB. No ECU codes, car starts fine. The main
>>> symptom was the drop in idle speed to 500rpm when the engine was cold
>>> and I was braking. Symptom went away after the car warmed up.
>>> Following the troubleshooting chart in my Helm's manual, I proceeded
>>> as follows:
>>> 1- Checked the resistance across the terminals of the EACV. Got
>>> 12ohms, within spec.
>>> 2- No continuity between each terminal and body ground - as expected.
>>> 3- Valve click when battery voltage is applied across the terminals.
>>> 4- Turned the ignition on, checked the voltage across the connector.
>>> There is 12V - not expected according to the manual since the ECU
>>> should be suppling the ground when EACV is activated. Confirmed by
>>> disconnecting the ECU harness that indeed ECU is suppling the ground.
>>> Put in another ECU - still voltage at EACV when ignition is on.
>>> Put in another EACV - same problem with idle
>>> New vacuum lines, bled the coolant - same problem with idle.
>>> Question: Is it true that there shouldn't be ground supplied to the
>>> EACV while the car is not running? The car was cold when I did these
>>> tests so is it possible that ECU checks the coolant temperature and
>>> decides to engage the EACV even if the car is not running?
>>> Any ideas?
>> the eacv has to be set to an airflow level where the car will start,
>> hence activation voltage before the motor is running.
>>
>> regarding symptoms, eliminate all other problems - this includes the
>> ignition system, plugs, ignition timing, etc. then go back to basics on
>> setting the warm idle properly. report back.- Hide quoted text -
>>
>> - Show quoted text -
>
> That makes sense that EACV is open at start up but I don't understand
> why it is conflicting with the service manual troubleshooting chart.
> General question: When are the output signals calculated by the ECU?
> Whenever the ignition is on or whenever the car is running?

i'd guess it's when the engine is running. the ecu's going to make
assumptions about air and fuel for ignition based on coolant temp and go
from there.

> As for the other items. The only thing I haven't checked so far is the
> ignition timing and I am planning on doing next week after I change my
> timing belt.

check the filter screen on the eacv too. if that's clogged, you're
going to get restricted flow. 89's have no screen, so i think it's safe
to remove it.