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Old 10-31-2012, 04:43 PM   #1
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Default Need a service-manual scan of EGR (94-97)

I am looking for a diagram of the vacuum side of the EGR system in a '94-'97 car. The EGR valve diaphragm, the vent/vacuum solenoids, and the functional path between them.

Any chance one of you faeries can hook me up?
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Old 10-31-2012, 06:06 PM   #2
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Sorry, just checked and my Haynes doesn't have any diagrams.
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Old 10-31-2012, 06:10 PM   #3
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A pox on your Haynes manual. (And the one I just ordered off of eBay for $1.99 plus $3.99 shipping.)
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Old 10-31-2012, 06:21 PM   #4
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Old 10-31-2012, 06:26 PM   #5
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Props to you, sir.
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Old 10-31-2012, 06:42 PM   #6
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Props indeed, that is precisely what I was looking for!



From looking at pictures of the actual parts, it appeared that the two solenoid valves were plumbed in series, and I thought "That's stupid- I must be looking at this wrong." This confirms that they are, in fact, in series.

So that, of course, raises the question in my mind: Why the heck did they bother having two solenoids when it would seem that one would suffice?

With a single solenoid of the type on the right, the ECU would be able to select between atmosphere or manifold vacuum. The only thing that adding the second solenoid does is to enable the selection of a third state: sealed off from both atmosphere and manifold vacuum.

What possible purpose can there be to such an arrangement?
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Old 10-31-2012, 09:19 PM   #7
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looks like ones a two and way and ones a three way/
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Old 10-31-2012, 09:26 PM   #8
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Quote:
Originally Posted by Joe Perez View Post
Props indeed, that is precisely what I was looking for!
1351719430[/IMG]

From looking at pictures of the actual parts, it appeared that the two solenoid valves were plumbed in series, and I thought "That's stupid- I must be looking at this wrong." This confirms that they are, in fact, in series.

So that, of course, raises the question in my mind: Why the heck did they bother having two solenoids when it would seem that one would suffice?

With a single solenoid of the type on the right, the ECU would be able to select between atmosphere or manifold vacuum. The only thing that adding the second solenoid does is to enable the selection of a third state: sealed off from both atmosphere and manifold vacuum.

What possible purpose can there be to such an arrangement?
More reason to put them in the garbage...or come up with a way to run EGR to increase fuel economy on my daily, and spell it out for me like I have the brain of a child.
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Old 11-01-2012, 01:41 AM   #9
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More reason to put them in the garbage...
Or to retrofit EGR into a vehicle which did not originally have it (such as 1990 Miata with an NB engine in it) for the purpose of running E85 in a high-compression configuration and yet still being able to pass a California emissions test.


Incidentally, who the hell is that girl in your avatar?
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Old 11-01-2012, 09:49 AM   #10
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How do you not know who Taylor Swift is? honestly.


I have a feeling the 2-way solenoid is an on/off, to simply open the EGR fully. Then the 3-way is a pwm signal to control the amount of flow. Why they couldn't have just used one is beyond me. But then again I'm just guessing.
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Old 11-01-2012, 10:21 AM   #11
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Props indeed, that is precisely what I was looking for!


Found using Google images surprisingly. I saw the diagram and it was the right year and everything!
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Old 11-01-2012, 10:27 AM   #12
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Incidentally, who the hell is that girl in your avatar?
One of my blondes.
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Old 11-01-2012, 10:32 AM   #13
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One of my blondes.
She's kinda Chicken-headin' it as of late.

Are you John Mayer?
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Old 11-01-2012, 01:50 PM   #14
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I have a feeling the 2-way solenoid is an on/off, to simply open the EGR fully. Then the 3-way is a pwm signal to control the amount of flow.
Hmm.

I'm torn here. PWMing the solenoid which is connected to the VTA would potentially introduce a vacuum leak into the system when the other solenoid was open.

On the other hand, PWMing the solenoid which is connected to the manifold would accomplish nothing, assuming that the other solenoid was fully open in the non-VTA position. (Regardless of PWM, the vacuum at the diaphragm would very quickly equalize at manifold pressure in the absence of a bleed, and I don't see a bleed anywhere in the system.)

Does the ECU in fact PWM this signal? I kind of assumed that since the EGR valve itself was vacuum-operated, that the position of the diaphragm would tend to automatically be proportional to manifold vacuum.

On the other hand, the presence of the EGR valve position sensor even in the pre-OBD II cars does suggest closed-loop operation.

I really wish I had a '94 - '97 car here to examine. Or at least a '94-'97 EGR valve to experiment with.
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Old 11-01-2012, 03:05 PM   #15
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Fly out to Rochester. You can inspect my system to your heart's desire.
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Old 11-01-2012, 03:16 PM   #16
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Originally Posted by Braineack View Post
How do you not know who Taylor Swift is? honestly.
Simple- I'm not a 13 year old girl. (I had to use Wikipedia to find out who Taylor Smith even was.)

Quote:
Originally Posted by rleete View Post
Fly out to Rochester. You can inspect my system to your heart's desire.
Yeah, about that...

No.
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