Vacum Issues
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Instructor
Joined: Jun 2009
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Vacum Issues
Hi, on my '85, this year I've had the heads off and the gearbox out, so not driven it much at all.
Having been back in the driving seat recently, I've found that the cruise control doesn't work and the air from the heater isn't getting through very well. I think both may be down to vacum, even the heater as the air flaps move under vacum. What do I need to look for and where?
Thanks in advance.
Having been back in the driving seat recently, I've found that the cruise control doesn't work and the air from the heater isn't getting through very well. I think both may be down to vacum, even the heater as the air flaps move under vacum. What do I need to look for and where?
Thanks in advance.
Thread Starter
Instructor
Joined: Jun 2009
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Just reading my manual as I'm looking to replace my injectors and it shows the two vacuum lines at the rear right hand of the plenum.
I'm trying to get more of an understanding of the vacuum system. Which out which of the two is for the HVAC and what does the other one do?
I'm trying to get more of an understanding of the vacuum system. Which out which of the two is for the HVAC and what does the other one do?
Thread Starter
Instructor
Joined: Jun 2009
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Thanks. I see, so, could explain why my heater flaps don't move anymore and the cruise doesn't work. When I switch the fan on with the slider, I take it there is a switch that electrically selects the fan on, but how does it work with the vacuum making the air flap change position?
Drifting
Joined: Aug 2002
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From: Birmingham AL
I think that there are little vacuum actuators at each flap. Follow the vacuum line from the rear of intake plenum and see if there it a tee with a built in check valve(Where it splits to go to hvac and cruise.). Not sure if an '85 has one of these, but it is a common issue for that tee to break or not function correctly.
Safety Car
Joined: Jan 2004
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Doesn't matter ;both see engine vac.
Line for HVAC runs to one way valve by dist
Rear line from valve goes to a plastic tube that is part of the wiring harness on firewall ,
to supply vac inside for HVAC controls.
Side port from valve goes to a T where it splits to the cruise unit and the rubber line continues along the inner wheel well to the vac ball under head light
Supplies vac for Fuel pressure reg and AIR
Line for HVAC runs to one way valve by dist
Rear line from valve goes to a plastic tube that is part of the wiring harness on firewall ,
to supply vac inside for HVAC controls.
Side port from valve goes to a T where it splits to the cruise unit and the rubber line continues along the inner wheel well to the vac ball under head light
Supplies vac for Fuel pressure reg and AIR
Last edited by vetteoz; Dec 9, 2010 at 07:42 PM.
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From: Murfreesboro Tn.
Doesn't matter ;both see engine vac.
Line for HVAC runs to one way valve by dist
Rear line from valve goes to a plastic tube that is part of the wiring harness on firewall ,
to supply vac inside for HVAC controls.
Side port from valve goes to a T where it splits to the cruise unit and the rubber line continues along the inner wheel well to the vac ball under head light
Supplies vac for Fuel pressure reg and AIR
Line for HVAC runs to one way valve by dist
Rear line from valve goes to a plastic tube that is part of the wiring harness on firewall ,
to supply vac inside for HVAC controls.
Side port from valve goes to a T where it splits to the cruise unit and the rubber line continues along the inner wheel well to the vac ball under head light
Supplies vac for Fuel pressure reg and AIR
Safety Car
Joined: Jan 2004
Posts: 3,556
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Gets brittle with age and commonly breaks off flush with the harness so you have to dismantle the harness to get enough length out to make a new connection
Thread Starter
Instructor
Joined: Jun 2009
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Right, I've taken some photos today as I'm doing a job and I've this is what I've got....
It shows my vacuum pipes taking a different route to some of the other diagrams shown above. So I've still yet to find out why the HVAC flap and cruise stopped working after the head gasket job, as everything appears to be connected, although I'm not sure if they're connected as they should be, I can't remember what it was like before as it wasn't me who did the heads.
Edit, here's the best photo I can find of before the heads, just look at those vacuum lines at the rear of the plenum!
And here's a close up
And compare that with todays (below), it clearly shows that the garage has put it back together wrong! I'd like to be able to sort this out myself, but I have no other information of how it was, the best photos I've got are what I've taken today.
It shows my vacuum pipes taking a different route to some of the other diagrams shown above. So I've still yet to find out why the HVAC flap and cruise stopped working after the head gasket job, as everything appears to be connected, although I'm not sure if they're connected as they should be, I can't remember what it was like before as it wasn't me who did the heads.
Edit, here's the best photo I can find of before the heads, just look at those vacuum lines at the rear of the plenum!
And here's a close up
And compare that with todays (below), it clearly shows that the garage has put it back together wrong! I'd like to be able to sort this out myself, but I have no other information of how it was, the best photos I've got are what I've taken today.
Last edited by Ant1981; Dec 11, 2010 at 12:28 PM.
Thread Starter
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I'm not sure if I'm reading this right, but it looks as though the garage have put the one way valve in the wrong way, cruise and HVAC lines are going to it, but they're connected to the fuel pressure reg, rather than out of the plenum and to the cruise and HVAC.
And as for the other output from the plenum, I've got to work out how it gets to the fuel pressure reg as it should and the air switching valve and air control valve on the diagram (will have to find out what that valve is too and where)
I do know that the belt driven air pump was disabled when the heads were done as over here we don't need it for emissions, so I think somewhere along the lines there is why the vacuum wasn't put back right.
And as for the other output from the plenum, I've got to work out how it gets to the fuel pressure reg as it should and the air switching valve and air control valve on the diagram (will have to find out what that valve is too and where)
I do know that the belt driven air pump was disabled when the heads were done as over here we don't need it for emissions, so I think somewhere along the lines there is why the vacuum wasn't put back right.
Last edited by Ant1981; Dec 11, 2010 at 03:38 PM.
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Vetteoz
Thanks for the vacuum diagram.
I saved it for future reference.
Mike
Thanks for the vacuum diagram.
I saved it for future reference.Mike
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From: Anaheim CA
That vacuum diagram is for a later '80s C4. I think it changed to that format in 1987.
The '85 has the EGR solenoid mounted on the passenger side rear of the intake manifold, as shown in the pictures above.
Another change from that diagram is that the PCV valve and canister purge vacuum come from the same source on the intake manifold next to the cold start injector.
From what I can see in the pictures, it looks like the two vacuum sources on the rear of the plenum are connected together. This is definitely wrong, as you observed. On my car the front vacuum port goes to the A.I.R. valve solenoids and also to the fuel pressure regulator. The rear vacuum port goes around the front of the distributor to the vacuum check valve shown in vetteoz's picture (that is a great picture and shows it perfectly).
The '85 has the EGR solenoid mounted on the passenger side rear of the intake manifold, as shown in the pictures above.
Another change from that diagram is that the PCV valve and canister purge vacuum come from the same source on the intake manifold next to the cold start injector.
From what I can see in the pictures, it looks like the two vacuum sources on the rear of the plenum are connected together. This is definitely wrong, as you observed. On my car the front vacuum port goes to the A.I.R. valve solenoids and also to the fuel pressure regulator. The rear vacuum port goes around the front of the distributor to the vacuum check valve shown in vetteoz's picture (that is a great picture and shows it perfectly).
Last edited by Cliff Harris; Sep 9, 2013 at 01:55 AM.
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From: Drums PA
Doesn't matter ;both see engine vac.
Line for HVAC runs to one way valve by dist
Rear line from valve goes to a plastic tube that is part of the wiring harness on firewall ,
to supply vac inside for HVAC controls.
Side port from valve goes to a T where it splits to the cruise unit and the rubber line continues along the inner wheel well to the vac ball under head light
Supplies vac for Fuel pressure reg and AIR
Line for HVAC runs to one way valve by dist
Rear line from valve goes to a plastic tube that is part of the wiring harness on firewall ,
to supply vac inside for HVAC controls.
Side port from valve goes to a T where it splits to the cruise unit and the rubber line continues along the inner wheel well to the vac ball under head light
Supplies vac for Fuel pressure reg and AIR
Oz: Is this diagram for a late '86 convertible as well? The previous owner must have replaced my upper radiator shroud at some point, and wound up putting on a 1987 part instead of a 1986 part. My emissions decal stats it meets requirement for a 1987 vehicle. Just wanted to make sure the '86's and '87's were the same before I changed over a few of the lines that looked like the previous owner may have screwed up on..........
Regards, Chris
