ES 250 1991 check engine code 71

Post by Jeff Daniels
I've started to get a regularly occuring check engine light. However the
car runs perfectly.
When I check the diagnastic code its always 71. That suppose to be an EGR
system malfunction. I've check all the EGR components, EGR valve cleaned
and tested, BVSV tested, EGR modulator cleaned and test, EGR gas temp.
senor tested and all ok. I pull the EFI fuse to reset the system and the
check engine light will stay out for several diagnostic code detection
like driving intervals...well not stickly but similar.
Anyone else experiencing this similar problem?
Stuart

How did you test the EGR valve?

How did you test the BVSV, EGR modulator, and EGR gas temp sensor?

--
Ray O
(correct punctuation to reply)

Jeff Daniels

2007-10-10 17:34:06 UTC

Post by Jeff Daniels
I've started to get a regularly occuring check engine light. However the
car runs perfectly.
When I check the diagnastic code its always 71. That suppose to be an
EGR system malfunction. I've check all the EGR components, EGR valve
cleaned and tested, BVSV tested, EGR modulator cleaned and test, EGR gas
temp. senor tested and all ok. I pull the EFI fuse to reset the system
and the check engine light will stay out for several diagnostic code
detection like driving intervals...well not stickly but similar.
Anyone else experiencing this similar problem?
Stuart

How did you test the EGR valve?
How did you test the BVSV, EGR modulator, and EGR gas temp sensor?
--
Ray O
(correct punctuation to reply)

Ray
I have a factory shop manual and basically followed the procedures for
testing the emissions controls.

The EGR valve was removed and tested on the bench. Negative presure from a
vacuum source was applied the EGR valve dashpot and the flow through the
valve was checked.

Differential presure was applied to modulator and modulator switch action
was verified.

The BVSV was tested with with a hot water bath and checking operation at 35
deg. C and 54 deg.

The EGR temp sensor was also bench tested with water bath.

Thanks,
Stuart

Ray O

2007-10-11 05:13:43 UTC

Post by Jeff Daniels
I've started to get a regularly occuring check engine light. However
the car runs perfectly.
When I check the diagnastic code its always 71. That suppose to be an
EGR system malfunction. I've check all the EGR components, EGR valve
cleaned and tested, BVSV tested, EGR modulator cleaned and test, EGR gas
temp. senor tested and all ok. I pull the EFI fuse to reset the system
and the check engine light will stay out for several diagnostic code
detection like driving intervals...well not stickly but similar.
Anyone else experiencing this similar problem?
Stuart

How did you test the EGR valve?
How did you test the BVSV, EGR modulator, and EGR gas temp sensor?
--
Ray O
(correct punctuation to reply)

Ray
I have a factory shop manual and basically followed the procedures for
testing the emissions controls.
The EGR valve was removed and tested on the bench. Negative presure from
a vacuum source was applied the EGR valve dashpot and the flow through the
valve was checked.
Differential presure was applied to modulator and modulator switch action
was verified.
The BVSV was tested with with a hot water bath and checking operation at
35 deg. C and 54 deg.
The EGR temp sensor was also bench tested with water bath.
Thanks,
Stuart

Good job on the checks! Try activating the EGR while the engine is idling
to see if the engine starts to run roughly. If there is no change, the EGR
is not opening sufficiently. You can also try temporarily disconnecting
vacuum hose from the EGR valve and plugging the vacuum hose to see if the
trouble code stays away.

--
Ray O
(correct punctuation to reply)

Jeff Daniels

2007-10-12 13:02:27 UTC

Post by Jeff Daniels
I've started to get a regularly occuring check engine light. However
the car runs perfectly.
When I check the diagnastic code its always 71. That suppose to be an
EGR system malfunction. I've check all the EGR components, EGR valve
cleaned and tested, BVSV tested, EGR modulator cleaned and test, EGR
gas temp. senor tested and all ok. I pull the EFI fuse to reset the
system and the check engine light will stay out for several diagnostic
code detection like driving intervals...well not stickly but similar.
Anyone else experiencing this similar problem?
Stuart

How did you test the EGR valve?
How did you test the BVSV, EGR modulator, and EGR gas temp sensor?
--
Ray O
(correct punctuation to reply)

Ray
I have a factory shop manual and basically followed the procedures for
testing the emissions controls.
The EGR valve was removed and tested on the bench. Negative presure from
a vacuum source was applied the EGR valve dashpot and the flow through
the valve was checked.
Differential presure was applied to modulator and modulator switch action
was verified.
The BVSV was tested with with a hot water bath and checking operation at
35 deg. C and 54 deg.
The EGR temp sensor was also bench tested with water bath.
Thanks,
Stuart

Good job on the checks! Try activating the EGR while the engine is idling
to see if the engine starts to run roughly. If there is no change, the
EGR is not opening sufficiently. You can also try temporarily
disconnecting vacuum hose from the EGR valve and plugging the vacuum hose
to see if the trouble code stays away.
--
Ray O
(correct punctuation to reply)

Hi Ray~

Yes, the EGR valve has always check out as you descibed. If you pump down
on the EGR vacuum hose, the engine will stumble when idling. Just to be
sure I took the EGR assembly off the car and cleaned it thoughly and
inspeced the operation. It looks good and operates smothly on the bench but
I suppose it could be binding or something at temperature.

By the way, I said hot water bath, I should correct that and say I actually
used motor oil. I have a little hot plate and an electronic themocouple
temperature sensor. Both the EGR temperature sensor and BVSV where within
the factory manual specifications.

So are you saying that if the EGR is closed (in the temporary disconnect
case) that the ECM won't see a fault? That's interesting.... I thought it
was monitoring the EGR temp sensor for a specific response vs. engine
temperature, vehicle speed, and or some such thing or other.

By the way, I'm now turning my attention to the vacuum port on the throttle
body. I can't remember if I checked that out now so I'm going back to that
this weekend and see what's going on there. I know its a bit of a long shot
but its at least due dilegence.

Thank for your feedback,
Stuart

Ray O

2007-10-13 02:41:47 UTC

Post by Jeff Daniels
I've started to get a regularly occuring check engine light. However
the car runs perfectly.
When I check the diagnastic code its always 71. That suppose to be an
EGR system malfunction. I've check all the EGR components, EGR valve
cleaned and tested, BVSV tested, EGR modulator cleaned and test, EGR
gas temp. senor tested and all ok. I pull the EFI fuse to reset the
system and the check engine light will stay out for several diagnostic
code detection like driving intervals...well not stickly but similar.
Anyone else experiencing this similar problem?
Stuart

How did you test the EGR valve?
How did you test the BVSV, EGR modulator, and EGR gas temp sensor?
--
Ray O
(correct punctuation to reply)

Ray
I have a factory shop manual and basically followed the procedures for
testing the emissions controls.
The EGR valve was removed and tested on the bench. Negative presure
from a vacuum source was applied the EGR valve dashpot and the flow
through the valve was checked.
Differential presure was applied to modulator and modulator switch
action was verified.
The BVSV was tested with with a hot water bath and checking operation at
35 deg. C and 54 deg.
The EGR temp sensor was also bench tested with water bath.
Thanks,
Stuart

Good job on the checks! Try activating the EGR while the engine is
idling to see if the engine starts to run roughly. If there is no
change, the EGR is not opening sufficiently. You can also try
temporarily disconnecting vacuum hose from the EGR valve and plugging the
vacuum hose to see if the trouble code stays away.
--
Ray O
(correct punctuation to reply)

Hi Ray~
Yes, the EGR valve has always check out as you descibed. If you pump down
on the EGR vacuum hose, the engine will stumble when idling. Just to be
sure I took the EGR assembly off the car and cleaned it thoughly and
inspeced the operation. It looks good and operates smothly on the bench
but I suppose it could be binding or something at temperature.
By the way, I said hot water bath, I should correct that and say I
actually used motor oil. I have a little hot plate and an electronic
themocouple temperature sensor. Both the EGR temperature sensor and BVSV
where within the factory manual specifications.
So are you saying that if the EGR is closed (in the temporary disconnect
case) that the ECM won't see a fault? That's interesting.... I thought it
was monitoring the EGR temp sensor for a specific response vs. engine
temperature, vehicle speed, and or some such thing or other.

I don't think the ECM will see a fault if the EGR is closed and temporarily
disconnected. Vehicles with OBD II have an EGR position sensor that checks
to see if the EGR is actually opening when called for, but I don't think
yours has one. I think the system uses the EGR temp sensor, but it takes a
while to throw a code.

Post by Jeff Daniels
By the way, I'm now turning my attention to the vacuum port on the
throttle body. I can't remember if I checked that out now so I'm going
back to that this weekend and see what's going on there. I know its a bit
of a long shot but its at least due dilegence.
Thank for your feedback,
Stuart

I admire the methodical way you are going about diagnosis. Fortunately (or
unfortunately, depending on your point of view) you have not left me with
any ideas as to the cause of the problem. I would check the "supply" vacuum
for the EGR modulator, perhaps using a vacuum gauge on a t-fitting to see if
it is getting sufficient vacuum for the modulator to work.

--
Ray O
(correct punctuation to reply)

Jeff Daniels

2007-10-13 20:59:48 UTC

Post by Jeff Daniels
I've started to get a regularly occuring check engine light. However
the car runs perfectly.
When I check the diagnastic code its always 71. That suppose to be an
EGR system malfunction. I've check all the EGR components, EGR valve
cleaned and tested, BVSV tested, EGR modulator cleaned and test, EGR
gas temp. senor tested and all ok. I pull the EFI fuse to reset the
system and the check engine light will stay out for several diagnostic
code detection like driving intervals...well not stickly but similar.
Anyone else experiencing this similar problem?
Stuart

How did you test the EGR valve?
How did you test the BVSV, EGR modulator, and EGR gas temp sensor?
--
Ray O
(correct punctuation to reply)

Ray
I have a factory shop manual and basically followed the procedures for
testing the emissions controls.
The EGR valve was removed and tested on the bench. Negative presure
from a vacuum source was applied the EGR valve dashpot and the flow
through the valve was checked.
Differential presure was applied to modulator and modulator switch
action was verified.
The BVSV was tested with with a hot water bath and checking operation at
35 deg. C and 54 deg.
The EGR temp sensor was also bench tested with water bath.
Thanks,
Stuart

Good job on the checks! Try activating the EGR while the engine is
idling to see if the engine starts to run roughly. If there is no
change, the EGR is not opening sufficiently. You can also try
temporarily disconnecting vacuum hose from the EGR valve and plugging the
vacuum hose to see if the trouble code stays away.
--
Ray O
(correct punctuation to reply)

Hi Ray~
Yes, the EGR valve has always check out as you descibed. If you pump down
on the EGR vacuum hose, the engine will stumble when idling. Just to be
sure I took the EGR assembly off the car and cleaned it thoughly and
inspeced the operation. It looks good and operates smothly on the bench
but I suppose it could be binding or something at temperature.
By the way, I said hot water bath, I should correct that and say I
actually used motor oil. I have a little hot plate and an electronic
themocouple temperature sensor. Both the EGR temperature sensor and BVSV
where within the factory manual specifications.
So are you saying that if the EGR is closed (in the temporary disconnect
case) that the ECM won't see a fault? That's interesting.... I thought it
was monitoring the EGR temp sensor for a specific response vs. engine
temperature, vehicle speed, and or some such thing or other.

I don't think the ECM will see a fault if the EGR is closed and
temporarily disconnected. Vehicles with OBD II have an EGR position
sensor that checks to see if the EGR is actually opening when called for,
but I don't think yours has one. I think the system uses the EGR temp
sensor, but it takes a while to throw a code.

I admire the methodical way you are going about diagnosis. Fortunately
(or unfortunately, depending on your point of view) you have not left me
with any ideas as to the cause of the problem. I would check the "supply"
vacuum for the EGR modulator, perhaps using a vacuum gauge on a t-fitting
to see if it is getting sufficient vacuum for the modulator to work.
--
Ray O
(correct punctuation to reply)

Ray~
I check out the throttle body E, R, and P ports for vacuum supply and they
are all OK. Vacuum source appears to be good and checks out through the
BVSV (after warm) to the modulator. I'm starting to turn my attention back
to the modulator. That's a really simple valve and I've had it apart for
cleaning and last time I looked appeared to be OK. I'm going to look at it
a bit closer next.

Stuart

Jeff Daniels

2007-10-20 15:16:07 UTC