Ported Vacuum Switches
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Junior User
Joined: Feb 2005
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From: Crosby
Ported Vacuum Switches
ok, I went to the junkyard and got all the vacuum lines that I needed to replace the broken ones. They come off of the vacuum switches on the rear driver's side of the motor, under the EGR and EVP. One vacuum line goes to the EGR valve, and 2 lines connect to the Thermactor System. and One, I don't know where it goes, but my guess is that It has to connect to the vacuum tree to supply vacuum to the ports but I'm not sure, Can anyone tell me where this one goes, It's the thicker black vacuum line. I have no vacuum to the ports, so I was thinking that maybe the ports are bad. Also when I hooked up the vacuum lines, The Thermactor system stopped working because of the no vacuum. This is on an 87 300-6.
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Joined: Sep 2004
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From: SC lowcountry
Look around the engine compartment carefully for a sticker with the vacuum diagram - if not there see if you can find someone with a similar truck preferably 87 so you can copy the diagram down. The service manuals do not show anything except a generic diagram; also appparently 87 was a pretty rapid transition period so there may even be changes during that model year. I will look further for anything in 88 manual but not sure i can come up with anything. Good luck.
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From: Crosby
there isn't a diagram anywhere. I think I know what's wrong, if the switches are bad, could they send a negative signal to the computer and instead of creating vacuum, it's blowing air out of the vacuum port. Anyone heard of this?
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Junior User
Joined: Feb 2005
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From: Crosby
nope. That's not it. The MAP Sensor connects right to the vacuum tree. This one comes right from the vacuum switches. There's a pinkish one, the thick black one, and a skinny black one. the pinkish and skinny black ones go to the air pump and i'm not sure where the other one goes.
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