Cowl Induction Questions - Chevelle Tech
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post #1 of 15 (permalink) Old Jul 14th, 02, 3:06 PM Thread Starter
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I have some questions for the cowl induction experts online at TC:

1)If the flapper opens when the engine turns off and closes when the engine starts does that prove that the vacuum part of the cowl induction is correct? I would think that it would but I'm not sure.

2) What would the symptoms be if the cowl induction relay was going bad? Flapper door not open?

3) What would the symptoms be if the cowl induction kick down switch was going bad? Flapper door not open?

4) What would the symptoms be if the cowl induction hood flapper door solenoid was going bad? Flapper door not open?

Reading I see that the cowl induction relay actuates the solenoid which in turns opens the flapper door but was wondering on the proper method to shoot trouble on these different parts to prove one was good or bad. Also could any of these items being defective cause any other problems other than the flapper not opening correctly?


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post #2 of 15 (permalink) Old Jul 14th, 02, 3:36 PM
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#1. If the flapper door opens when the engine shuts off and closes upon starting...then your vacuum pod and hoses are fine. That is the only thing that controls the outer flapper door.

Any problems with the solenoid or kick down switch would be noted if the inner door doesn't open.

Open your hood (makes it easier to see inner door), turn your ignition on (you do not have to start the engine), push all the way down on your gas pedal and the inner door should open.

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post #3 of 15 (permalink) Old Jul 14th, 02, 3:46 PM Thread Starter
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Thanks for the quick response RC 70. I will do that quick test.
Do you know what the symtoms would be if any if the inner door wouldn't open? Only the flapper not opening?

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post #4 of 15 (permalink) Old Jul 14th, 02, 3:55 PM
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If the inner door doesn't open I would strongly suspect the solenoid was bad.

If the flapper doesn't open the vacuum pod is probably bad.



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post #5 of 15 (permalink) Old Jul 14th, 02, 4:02 PM Thread Starter
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Would the inner door not opening cause the engine to run differently? Would the car act like it's running out of gas or any other symptoms that you're aware of? I really appreciate the help RC 70. BTW, nice car!

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post #6 of 15 (permalink) Old Jul 14th, 02, 4:22 PM
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Engine should run fine without the inner door opening, it would only restrict air flow at wide open throttle. It should not act as if it is running out of gas or any other symptoms during normal cruising and you may not notice much difference at WOT.

Glad to help. Hope you get it worked out.

BTW your ride is pretty sweet too!

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post #7 of 15 (permalink) Old Jul 14th, 02, 4:49 PM Thread Starter
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Thanks for the cowl induction 101 class. I know more about it now than before!

I'm not really having any troubles that I could pin point back to the cowl induction because it seems to be working ok. I was after a better understanding of it which you gave me!

The problem I have been having lately is four different times now my car has acted like its running out of gas for a few seconds (5-10) and be fine afterwards. Only once has it actually stalled but it started right back up with no problems the rest of the night. Neither time was it really hot where I could blame it on vapor lock. Yesterday it happened while driving it on the highway at a steady 70 mph (thanks to my 323 gear . Since then I drove it in the July 4th parade and had no problems at all. Then yesterday it did it again. The car starts good and runs good and has no hessitation but this has me worried that one time it's going to stall and not start. My experience with fuel pumps in the past is that they just go out completely so I don't think its a fuel pump but I could be wrong. I'm thinking possibly a fuel filter but who knows? It is so strange that it does it and then quits for a few days or a week or two. Any suggestions or thoughts on this?

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post #8 of 15 (permalink) Old Jul 14th, 02, 5:01 PM Thread Starter
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Open your hood (makes it easier to see inner door), turn your ignition on (you do not have to start the engine), push all the way down on your gas pedal and the inner door should open.

Well, I did this test and the inner door didn't open so I guess I do have a problem.
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post #9 of 15 (permalink) Old Jul 15th, 02, 6:03 PM Thread Starter
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Correct me if I'm wrong, but is there 12 volts standing on one side of the Kickdown Switch and when you push the pedal to the floor 12 volts would then go through the Kickdown Switch and to the Solenoid which would then open the inner door? Am I right on this logic as I try to determine if I have a bad Kickdown Switch or bad solenoid? Thanks again for all of your assistance!

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post #10 of 15 (permalink) Old Jul 16th, 02, 8:14 PM
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yes, i believe you are correct just check the switch for voltage on both sides, then press the plunger down on it and check again, you should have pos. on both sides then and only on 1 side before. if you have voltage, then check for voltage at the silenoid. if you have it there check it's ground if it has ground then the silenoid is bad.

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post #11 of 15 (permalink) Old Jul 16th, 02, 8:47 PM Thread Starter
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Thanks chev-hell. Just by looking at it closely, I figured that was the way it had to work. I have a 1971 Chassis Service Manual but it doesn't even discuss cowl induction at all nor does any of the wiring diagrams that are in it. The puzzling thing to me is why does the cowl induction open up when I step on it if one of those parts would be bad. RC 70 told me in this thread that the vacuum only controls the outer door and it opens and closes on startup and shutdown ok and even opens up when I step on it.
Just so I understand it even better, I guess that leads me to another question. Is the outer door flapper still being controlled by the vacuum line only when you step on it to open?
BTW, nice website John! Why did you sell the one Chevelle to buy another? Your old one looked pretty good too!

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post #12 of 15 (permalink) Old Jul 16th, 02, 8:50 PM
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When you romp on the gas, you lose vacuum and again the door will open. No or little vacuum...door opens. Vacuum...door is closed.

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post #13 of 15 (permalink) Old Jul 16th, 02, 9:01 PM Thread Starter
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Thanks RC 70. I guess it's exactly like you said, the vacuum line is only for the outer door and only the vacuum line operates it. I really appreciate your answering all of my questions. It's too bad my 1971 Chassis Service Manual doesn't address cowl induction. Lucky for me I have TC huh?

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post #14 of 15 (permalink) Old Jul 17th, 02, 12:09 AM
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No Problem Bill. Glad to help out. I have my share of questions and someone always helps me out. That's the whole idea
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post #15 of 15 (permalink) Old Aug 5th, 02, 9:27 PM Thread Starter
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Thought I'd give a followup on this. The problem ended up being a bad wire connection at the solenoid. Problem solved.
I still haven't had a chance to investigate the problem of the car acting like its running out of gas yet. I have drove it at least 200 miles since the last time it acted up. Thanks again to all for the replies! TC is great!

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