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Discussion Starter · #1 ·
Hey all, need a lil help. 03 2500 5.9. Cruise quit working, so I read and read and read about vacuum lines. Sure enough I had a hole. Replaced line and cruise works. Thanks to all.
That being said, my vacuum pump still runs continuously. If I block off the tee going through the firewall, it stops running.
The question is, what does the vacuum line going into the firewall control? I can’t find it under the dash. My hvac system seems to be working, so I’m a little lost. I don’t want to burn the vacuum pump, but don’t know what to do.
Any help would be appreciated.
 
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The 2003 trucks have a fully electric HVAC system, nothing to do with vacuum.

I can't think of a reason why a vacuum line is going into the cab on a 2003 truck.
Does the T and the line look factory?
Perhaps a previous owner had a temp vacuum gauge while trouble shooting the vacuum controlled cruise control?

I would be tearing the dash apart trying to figure it out.
I guess you could block that line and then see what is not working in the cab.
 

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Discussion Starter · #3 ·
It’s factory. I blocked it off and the pump doesn’t run continuously anymore, but the cruise doesn’t work either. Is there a vacuum reservoir in there somewhere?
 
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It’s factory. I blocked it off and the pump doesn’t run continuously anymore, but the cruise doesn’t work either. Is there a vacuum reservoir in there somewhere?
Now you need the factory service manual to figure this out. The manuals are on this forum for downloading.

I don't think there is a reservoir but who knows. There could be a control module that is monitoring the vacuum levels and also controlling the cruise control.

Sorry I'm not much help, my 2004.5 truck does not use vacuum for cruise control.


Edit: So I looked it up in the 2004 on-line service manual.

The manual states that there is vacuum reservoir under the fresh air cowl panel.
Under the plastic panels, under the wiper arms.
The picture shows a rectangular shaped vacuum reservoir.

Font Material property Parallel Rectangle Engineering
 
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