Mystery vacuum hose on Chevy van

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Old 07-23-16, 05:52 PM
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Mystery vacuum hose on Chevy van

2000 chevy express, 1500, 1/2 ton, 5.0 v8

There is a 1/4" vacuum hose hanging under the van near the passenger door. I see a diafram along that side of the van but there is a smaller vacuum already connected to it. It can't go to the transmission AFAIK since that year doesn't have a vacuum modulator valve. Does anyone know where it goes?
 
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Old 07-23-16, 07:41 PM
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Do you see any storage canisters mounted to the frame near there ?
It may be some type of fuel vapor storage vent line although usually it's 5/16" line.

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Old 07-24-16, 05:23 AM
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I didn't see that but I'll look again. There was something in the fuel line but it was round & had a smaller hose already connected to it. I looked to see if it had a place for a second hose. I didn't see anything. I'll have to look at that again too.
 
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Old 07-24-16, 07:18 AM
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Where does it come from?
Is there vacuum on the hose when the engine is first started?

Where it comes from could tell you where it might go.
 
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Old 07-24-16, 07:57 AM
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I haven't followed it all the way but it runs up along the fuel lines. I imagine that it goes to the intake manifold. I haven't checked the vacuum in it either. I just bought the van. It runs smoothly as if there were no vacuum leak at all.
 
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Old 07-24-16, 11:01 AM
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There is a 50/50 chance it just runs to the intake manifold.......there are several sensors that could control vacuum on that hose for operating and pollution purposes.
Some allow vacuum when engine cold and none when hot and vice versa.

The exhaust bypass in the intake manifold is one example that allows vacuum when cold to bypass exhaust until engine warms up.
 
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Old 07-24-16, 03:47 PM
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Edit: I'm going to look at it now.

Edit #2: You aren't going to believe it. It looks like the other end of the hose is hanging in front of the motor mount. The hose may have been replaced & the old hose was left hanging.
 

Last edited by donoli2016; 07-24-16 at 04:08 PM.
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