EGR Valve

Hi

I just wanted to know what exactly an EGR valve does, and if there is
one that is not working properly in a car, what damage is possible.
This is a civic engine...non VTEC. Anybody??

"contagiouss_blue" > wrote in
ups.com:

> Hi
>
> I just wanted to know what exactly an EGR valve does, and if there is
> one that is not working properly in a car, what damage is possible.
> This is a civic engine...non VTEC. Anybody??
>


What year Civic?

The EGR valve is an emission control device for the purpose of lowering
oxides of nitrogen (NO, NOx). EGR has no role to play other than emissions.

The EGR valve (and its associated control hardware and gas passages)
provides the metering of small amounts of spent exhaust gases back into the
combustion chamber in order to lower combustion temperatures and thus
oxides of nitrogen.

If this device fails or clogs shut, your NO readings will increase and you
may fail an emissions test. If it sticks open, you can suffer poor
driveability and stumbling at part-throttle.

If the device fails shut, it is possible for combustion temperatures to
increase to the point that damaging detonation occurs, since the engine
control computer is expecting that the EGR is functional. This is less
likely on post-'95 cars, which have knock sensors.

If your car is a 1996 or later, EGR problems will turn on the MIL (Check
Engine light) with an OBD-II code of P04xx, P14xx, or P24xx. The Check
Engine light on earlier cars will not necessarily illuminate when the EGR
malfunctions.

--
TeGGeR®

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

my 98 civic (non vtec though) does not have an EGR valve.

EGR is only needed if your Honda is an automatic. Stick cars
don't need it because they don't waste a lot of fuel running
the transmission during idling.

disallow wrote:
>
> my 98 civic (non vtec though) does not have an EGR valve.

contagiouss_blue wrote:
>
> Hey..thakns a lot for the info, its really appreciated. I have a 96
> civic and my engine check light does come on. I have had the problem
> identified by a mechanic...it seems that the valve itself is fine but
> the electronic sensor attached to it has malfunctioned. So I was
> wondering wether to get the whole thing replaced...is the engine check
> light the only indicator that tells me if my EGR is working, or is
> there some other way to monitor it?

Typically, the EGR valve is controlled closed-loop by the ECU. The ECU
applies a signal to the EGR valve and then reads the feedback from the
sensor to see how far open the valve is. The ECU then modifies the drive
signal until it reads back the correct valve-opening (for the current
operating conditions) from the sensor. So with a broken sensor, even
tough the valve can still open and close, the EGR system is not working
properly. Unlike the second O2 sensor, which only function is to turn on
the check engine light, the EGR valve sensor is part of the emissions
control loop.
--
================================================== =====
A very modest collection of Honda tech info can be found at:
http://www.geocities.com/ng_randolph

Sean Dinh wrote:
>
> EGR is only needed if your Honda is an automatic. Stick cars
> don't need it because they don't waste a lot of fuel running
> the transmission during idling.

Honda has used EGR valves on both automatics and stick shifts. The 1994
Civic VX manual had an EGR valve, the 1994 Civic EX Automatic did not.

A bad/failing O2 sensor will cost you several MPG.
BTDT
And try passing a rigouris emission test without one.

The EGR is to manage NOX emmisions.
Terry

"contagiouss_blue" > wrote in
oups.com:

> Hey..thakns a lot for the info, its really appreciated. I have a 96
> civic and my engine check light does come on. I have had the problem
> identified by a mechanic...it seems that the valve itself is fine but
> the electronic sensor attached to it has malfunctioned. So I was
> wondering wether to get the whole thing replaced...is the engine check
> light the only indicator that tells me if my EGR is working, or is
> there some other way to monitor it?
>


What does your mechanic say? More importantly, what was the OBD-II code
number?

Sometimes the valve itself is fine, but the exhaust gases carbon-up the
passages and sensors, causing problems.

There are various tests that can be applied to test the parts of the EGR
system. For example, the EGR valve is vacuum-controlled. If you apply
vacuum directly to the EGR valve while the engine is idling, the engine
should stumble badly or stall. If the idle does not change, then the valve
is carboned up.

What's that error code? Should be something like Px4xx (where x is a
number)

--
TeGGeR®

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

wrote in
oups.com:

> A bad/failing O2 sensor will cost you several MPG.
> BTDT


Yeah, about 1-2 mpg per year if you drive a lot.


> And try passing a rigouris emission test without one.
>
> The EGR is to manage NOX emmisions.



Terry, I wish you would turn quoting back on.

Randolph was referring to the *after-cat* O2 sensor, not the pre-cat one.
Very different function.

--
TeGGeR®

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

What are the respective purposes of the pre and
post cat O2 Sensors? My little brothers pre cat
o2 sensor was unplugged on his 93 Nissan
Altima. How would this affect engine operation
and economy? (I did plug it back in, hopefully
it was unplugged for no good reason) (Also, it
only had 1 wire.)

Thanks
t