ES 250 1991 check engine code 71

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Jeff Daniels - 09 Oct 2007 19:14 GMT

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

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Ray O - 10 Oct 2007 04:20 GMT

> I've started to get a regularly occuring check engine light. However the
> car runs perfectly.
[quoted text clipped - 9 lines]
>
> Stuart

How did you test the EGR valve?

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

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Ray O
(correct punctuation to reply)

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Jeff Daniels - 10 Oct 2007 18:34 GMT

>> I've started to get a regularly occuring check engine light. However the
>> car runs perfectly.
[quoted text clipped - 13 lines]
>
> How did you test the BVSV, EGR modulator, and EGR gas temp sensor?

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

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Ray O - 11 Oct 2007 06:13 GMT

>>> I've started to get a regularly occuring check engine light. However
>>> the car runs perfectly.
[quoted text clipped - 31 lines]
> 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.

Signature

Ray O
(correct punctuation to reply)

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Jeff Daniels - 12 Oct 2007 14:02 GMT

>>>> I've started to get a regularly occuring check engine light. However
>>>> the car runs perfectly.
[quoted text clipped - 37 lines]
> disconnecting vacuum hose from the EGR valve and plugging the vacuum hose
> to see if the trouble code stays away.

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

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Ray O - 13 Oct 2007 03:41 GMT

>>>>> I've started to get a regularly occuring check engine light. However
>>>>> the car runs perfectly.
[quoted text clipped - 54 lines]
> 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.

> 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
[quoted text clipped - 3 lines]
> 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.

Signature

Ray O
(correct punctuation to reply)

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Jeff Daniels - 13 Oct 2007 21:59 GMT

>>>>>> I've started to get a regularly occuring check engine light. However
>>>>>> the car runs perfectly.
[quoted text clipped - 81 lines]
> 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~
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

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Jeff Daniels - 20 Oct 2007 16:16 GMT

This turned out to be the EGR BVSV valve afterall. I had check this valve
out before and put it back on the engine. I then removed the EGR itself and
cleaned it. When testing the engine I had assumed that cleaning the EGR
valve was not the problem because the 71 code came back.

Apprently the nipples on the BVSV valve where old and brittle and one of
them broke after reinstalling the hoses. The real problem was the sticky
EGR valve which was cleaned but in the interim the BVSV had failed.

So I'd have to say if you follow the manual carefully and check your work
you can fix this problem.

Stuart

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