EGR cycling on and off when idling
Ryan Doyle
on and off which in turn is messing up my idle speed. Up and down, up and
down but sometimes just up - around 1500 RPM. What may be causing the
computer to cycle this on and off? I have removed the vacuum hose from the
EGR and it is working but sucking gas like crazy right now. Advice would be
appreciated.
--
Ryan
Jonathan Race
sensor. First step is to replace the O2 sensor which typically has a
recommended replacement interval of approx. 30,000 miles. It is mounted
onto the exhaust pipe downstream of the exhaust manifold (some vehicles had
it mounted directly into the manifold). It should cost about $50-60, is
connected by one wiring plug, and take about 10 minutes with an open-end
wrench and a dab of anti-seize compound.
Second is to obviously replace the EGR valve. It may be sticking or have an
internal leak. Sorry, I don't know the cost but I do know that
www.carparts.com had an EGR for my '95 Chevy for less than half of what the
dealer's parts department wanted, for the same brand name.
Good luck - Jonathan
--
Acta Non Verba - Deeds Not Words
Lieutenant Jonathan Race, EMS Supervisor
Orange County (FL) Fire-Rescue Department
"Ryan Doyle" <RRR...@hotmail.com> wrote in message
news:Xns9199801BA2AEA...@207.181.101.12...
tony
<jr...@bitstorm.net> wrote:
> Primary EGR function is controlled by the ECM and regulated by the
> oxygen sensor. First step is to replace the O2 sensor which typically
> has a recommended replacement interval of approx. 30,000 miles.
Well if the O2 sensor was out of range enough to affect engine operation
why would the ECM set a O2 error code?
Robert Hancock
Usually if the EGR valve is opened when the engine is idling it will cause
the engine to run rough or stall, I haven't heard of it increasing the idle
speed. Are you saying it idles normally with the EGR vacuum hose removed?
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Ryan Doyle" <RRR...@hotmail.com> wrote in message
news:Xns9199801BA2AEA...@207.181.101.12...
Jonathan Race
> Well if the O2 sensor was out of range enough to affect engine operation
> why would the ECM set a O2 error code?
Answer - If the O2 sensor was out of range enough to affect engine
operation, then the ECM would (should) set an O2 error code.
Hope that helps some - Jonathan
tony
<jr...@bitstorm.net> wrote:
> Let my provide an answer by re-wording your question:
>
>> Well if the O2 sensor was out of range enough to affect engine
>> operation why would the ECM set a O2 error code?
>
> Answer - If the O2 sensor was out of range enough to affect engine
> operation, then the ECM would (should) set an O2 error code.
>
Are you suggesting that you should change the o2 sensor even if there is
no O2 error code?
Jonathan Race
that the O2 sensor is bad because it only determines this by reference
voltage which may not yet be out of range but still fluctuating widely
enough to cause drivability problems. Additionally, the ECM does not always
use O2 sensor input to adjust engine operating parameters, only when the
motor is at its proper operating temperature and it is running in "open
loop" mode. If the engine is cold (and/or the O2 sensor has not heated up
enough, which could occur because of extreme carbon build-up on the sensor
tip), then the motor is running in "closed loop" mode and the settings for
many of the engine controls are being determined by the preprogrammed memory
and not sensor inputs.
If the original poster has determined that the EGR valve is the culprit,
then my entire point is for him to realize that the EGR valve and the O2
sensor are closely related. Maybe I should have mentioned this earlier, but
he could also have a faulty IAC (Idle Air Control) valve, sometimes referred
to as an Idle Speed Motor, which allows air to bypass the throttle body
injectors and raise/lower idle speed. Additionally, a faulty coolant
temperature sensor *may* cause something similar to this but not nearly as
likely as the EGR, O2, or IAC.
Cheers - Jonathan
--
Acta Non Verba - Deeds Not Words
Lieutenant Jonathan Race, EMS Supervisor
Orange County (FL) Fire-Rescue Department
"tony" <g...@echo.com> wrote in message
news:pan.2002.01.19.0...@echo.com...
Neil Nelson
<jr...@bitstorm.net> wrote:
>Yes, it's called preventative maintenance. The ECM may also not realize
>that the O2 sensor is bad because it only determines this by reference
>voltage which may not yet be out of range but still fluctuating widely
>enough to cause drivability problems. Additionally, the ECM does not always
>use O2 sensor input to adjust engine operating parameters, only when the
>motor is at its proper operating temperature and it is running in "open
>loop" mode. If the engine is cold (and/or the O2 sensor has not heated up
>enough, which could occur because of extreme carbon build-up on the sensor
>tip), then the motor is running in "closed loop" mode and the settings for
>many of the engine controls are being determined by the preprogrammed memory
>and not sensor inputs.
If I'm reading this correctly (and I believe I am), you're saying that a
cold O2 or a carboned up
O2 constitutes running in closed loop and a motor and sensor running at
its proper operating
temperature is open loop?
Sorry, but that's backwards.
>If the original poster has determined that the EGR valve is the culprit,
>then my entire point is for him to realize that the EGR valve and the O2
>sensor are closely related. Maybe I should have mentioned this earlier, but
>he could also have a faulty IAC (Idle Air Control) valve, sometimes referred
>to as an Idle Speed Motor, which allows air to bypass the throttle body
>injectors and raise/lower idle speed. Additionally, a faulty coolant
>temperature sensor *may* cause something similar to this but not nearly as
>likely as the EGR, O2, or IAC.
On this particular set up, the EGR solenoid is fed manifold vacuum, the
ECM controls
whether vacuum is allowed to the EGR diaphram. A pulsing EGR with its
related idle 'hunting'
would suggest that the quad driver that controls the EGR solenoid has
shorted from excessive
current flow. Now the search begins to determine where the shorted
winding is, the EGR quad
driver is usually if not always shared with another output device such as
the TCC solenoid or
an air pump solenoid. (reference GMs solenoids can't go below 20 ohms rule
that's been in effect
for the last 24 years). If the EGR solenoid is in spec (over 20 ohms)
then going around and unplugging
all the other output devices would be the next step... Once you unplug the
offending device, the
EGR solenoid -may- begin behaving properly.
Then again, maybe he's got the typical "sucked in" TBI base gasket and
that is the reason for the hunting idle.
(don't think I've seen that mentioned yet in this little pissing match).
Ryan Doyle
news:Y2228.14457$467.5...@news2.calgary.shaw.ca:
> What kind of EGR system is this, controlled by a vacuum solenoid?
>
> Usually if the EGR valve is opened when the engine is idling it will
> cause the engine to run rough or stall, I haven't heard of it
> increasing the idle speed. Are you saying it idles normally with the
> EGR vacuum hose removed?
>
> --
> Robert Hancock Saskatoon, SK, Canada
> To email, remove "nospam" from hanc...@nospamshaw.ca
> Home Page: http://www.roberthancock.com/
Yes, controlled by vac solenoid. For the most part it changes its idle
speed up and down in about a 2 second wave - 1 high, 1 low. The actual EGR
is opening and closing. I see it on the scanner.
>> --
>> Ryan
>
>
--
Ryan and Linda Doyle
Embrun, ON
2000 Bayside
1995 Suburban
6 and 9 year-olds
Ryan Doyle
12:
Sorry. Yes it idles fine with the vac hose removed and plugged.
Jonathan Race
Send button but I didn't bother with a follow-up to my own post because I
knew someone would correct me.
Cheers - Jonathan
--
Acta Non Verba - Deeds Not Words
Lieutenant Jonathan Race, EMS Supervisor
Orange County (FL) Fire-Rescue Department
"Neil Nelson" <none...@execpc.com> wrote in message
news:3c49cdc0$0$43572$272e...@news.execpc.com...
Robert Hancock
idle speed?
Also check the TPS and MAP sensor readings, see if they're obviously off or
unstable at a constant engine speed. If the ECM is commanding the EGR to
open, then something's probably giving it some bad information that's
causing it to do this..
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Ryan Doyle" <RRR...@hotmail.com> wrote in message
news:XnsFFFFFFFFFFFE556CFFFFFFFFF...@207.181.101.12
...
Jonathan Race
news:3c49cdc0$0$43572$272e...@news.execpc.com...
>
> that is the reason for the hunting idle.
> (don't think I've seen that mentioned yet in this little pissing match).
Sorry for not reading your post till the bitter end, Neil. The "sucked in"
TBI gasket as you call it is actually a crack in the base gasket that sits
between the TBI and the intake manifold. The crack allows air in on the
manifold side of the TBI and increases idle. What happens is the ECM senses
this and shuts the IAC valve to try to lower the idle RPM, but as the crack
gets bigger the idle continues to increase despite the IAC being closed.
However, this typically results in a higher idle only (which may or may not
go away as the motor and related parts heat up and expand) and not in a
'hunting' or 'surging' idle as was described. Although it did occur to me
that the EGR valve may not be the cause but instead just be reacting to the
surging idle speed, it was the original poster who determined that it was
the EGR valve causing the problem - and who am I to disagree. After all,
it's his truck, not mine. The cracked gasket happened to my old '88 C1500
with a 350 and it was easy enough to fix, but I believe that the new gasket
which fixed much of the problem came out in '92.
EGR valves can sometimes be a tricky lot. On my current '95 6.5L
turbo-diesel, the incorrect EGR was used (one for a non-turbo motor) and
would cause - of all things - my torque converter to rapidly lock and unlock
between 45 and 50mph. Annoying to say the least. Someone on one of these
newsgroups told me about the new EGR valve, I replaced it myself, and the
problem was solved - 60,000 miles ago. I don't pretend to fully understand
or agree with the explanation that was given for this problem, but the
solution worked and I'm happy, which is all that counts.
Good luck - Jonathan