Need a service-manual scan of EGR (94-97)
10-31-2012, 03:43 PM
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Boost Pope
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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?
Any chance one of you faeries can hook me up?
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10-31-2012, 05:21 PM
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These? Could be wrong...
http://www.scrabblegod.com/locost/wiring/mvd1.jpg
http://www.scrabblegod.com/locost/wiring/mvd2.jpg
http://www.scrabblegod.com/locost/wiring/mvd1.jpg
http://www.scrabblegod.com/locost/wiring/mvd2.jpg
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10-31-2012, 05:42 PM
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Boost Pope
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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?
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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10-31-2012, 08:26 PM
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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?
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?
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11-01-2012, 12:41 AM
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Boost Pope
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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?
Incidentally, who the hell is that girl in your avatar?
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11-01-2012, 08:49 AM
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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.
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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11-01-2012, 12:50 PM
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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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