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  1. #1
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    Corvette(s)
    1986 CORVETTE

    Default 86 vacuum line diagram? for tpi

    does anyone have a vacuum line diagram for a 86 5.7 tpi? there is an electric switch that is connected to a bracket that bolts onto the thermostat housing.. it looks like a vacuum line is supposed to connect there also but i cannot find anything missing or off... but i do hear a vacuum leak from under the tpi.. any help would be appreciated.. i am going nuts looking for it!!

  2. #2
    rrubel's Avatar
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    Corvette(s)
    1986 Bright Red Coupe

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    That's the EGR control solenoid. There should be two vacuum lines going to it, IIRC. One goes straight up to the bottom of the throttle body, one goes under the plenum to the EGR valve.

    [RICHR]

  3. #3
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    thanks.... now... does anyone have a diagram of how the lines are supposed to run??

  4. #4
    rrubel's Avatar
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    There's no real need for a diagram; I have one but it's real simple. There's a line from the bottom of the throttle body to the left port on the front of the solenoid, and a line from the right port on the solenoid to the EGR valve under the middle of the plenum. The diagram shows three boxes with two lines connecting them plus one electrical connector, plus the EGR pipe. And this is the factory service manual.

    Now if you want a PHOTO, that might help more. However, mine's not stock and you can't see where the EGR valve is. It's difficult to get to in any case without removing the plenum, but if you shine a light between the middle runners (try from the driver's side) you'll see something that looks like a flying saucer with a nipple on one side. That's the EGR valve. Chances are, the black vac line is cracked somewhere near the valve and the other piece fell out of the solenoid and got lost. On the front of the solenoid are two holes; the left one goes to the throttle body (just almost straight up) and the right one curves around and to the egr by the shortest path. There's no real RUNNING that they do and the diagram certainly doesn't show it.

    [RICHR]

  5. #5
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    1986 CORVETTE

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    thanks... there was a hose that was up under the plennum and the the one to the throttle body wasnt even there... i hooked both up with no problem.. thanks to your knowledge about this... thought this was going to solve the vacuum leak i was hearing all this time..unfortunatly its still there.. can hear it still from under the plennum... but i appreciate the help.. hooking those lines back up the right way might solve the idle issue.. i hope

  6. #6
    rrubel's Avatar
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    Any vacuum leak will definitely mess up your idle... The only other things running under the plenum that I can remember are the line to the fuel regulator (passenger side, at the rear, behind the EGR- metal dome, might be painted black, one vac line) and two lines that come off the back of the plenum, also on the passenger side. One should go to the brake system (crosses under OR goes behind the distributor), and I think the other comes forward to something on the A/C system. If you can borrow (or own) a vacuum gauge, hook it up to one of the fittings behind the plenum and watch what it's doing. It should be stable at 20 mm/HG at idle.

    It's also possible that you're pulling air through a leaking gasket under the plenum. The lower runners meet up with the intake manifold and can occasionally leak, and the intake manifold gasket may too, where it meets the heads (you'd probably be leaking some coolant as well, though, if that one were going).

    Buy a can of carbuerator cleaner (hopefully one that comes with a little straw) and (with the engine running) spray little bursts around the base of where the runners meet the intake manifold. If you hear your idle increase while you're spraying at a particular spot, you've found your leak.

    Good luck; I chased a manifold leak for a couple weeks after my engine rebuild. I've also had several of the black plastic vac lines just fall apart when I touched them - they don't age well. Fortunately, last I checked you can still order them from GM. However, I replaced almost all of mine with hi-temp silicon hose. It's fatter, but should last longer in the heat, and it's colored to match the car .
    [RICHR]

  7. #7
    Member hawker4611's Avatar
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    Corvette(s)
    1986 Convertable 1990 Coupe

    Default Vacuum line to nowhere

    Hey rrubel, I just bought an 86 convertable and have an open vac lin at the distributor area. 1 large braided line coming out of the right side of the upper manifold crossing over to the left in front of the distributor to a TEE. From there, 1 medium rubber line goes down to the accumulator in front of the left tire. The other small rubber line enters a plastic line and goes around the back of the Distributor by the oil preesure sensor and back to small rubber after 6 to 8 inches. THATS where it ends!!!!!! Vac leak for sure, but what does this line go to???? Thanks

  8. #8
    Member Schrade's Avatar
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    Quote Originally Posted by hawker4611 View Post
    Hey rrubel, I just bought an 86 convertable and have an open vac lin at the distributor area. 1 large braided line coming out of the right side of the upper manifold crossing over to the left in front of the distributor to a TEE. From there, 1 medium rubber line goes down to the accumulator in front of the left tire. The other small rubber line enters a plastic line and goes around the back of the Distributor by the oil preesure sensor and back to small rubber after 6 to 8 inches. THATS where it ends!!!!!! Vac leak for sure, but what does this line go to???? Thanks
    The cruise control vacuum reservoir and the EVAP cannister are both drivers side in front of the wheel well.

    EVAP cannister has a line going to the intake, which feeds to the intake through the EGR. I don't know where the 'T' is, but start at the EGR valve and follow the vacuum line. It should go to the 'T' which splilts off to the exhaust gas source, and the other to the EVAP cannister.

    The 'T' could be the vacuum solenoid itself, which redirects vacuum.

  9. #9
    Member hawker4611's Avatar
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    Corvette(s)
    1986 Convertable 1990 Coupe

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    Hi Shrade, This small TEE is right at the distributor and has the medium line going down to the round accumulator ball in front of the left front tire. The small line goes around behind the distributor using a plastic pipe like tube heading for the passenger side right up against the firewall. On the open end is a short 4" small hose again. This TEE is just above the steel line headed over to the Brake Vac Assy. Can't see anything on the right side, but can't see up against the firewall much at all!!!

    Just bought this Torch Red conv. and happy as can be. My life long dream has come true at 61 yrs. young!!!

  10. #10
    Member Schrade's Avatar
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    Welcome onto the boards there!

    I thought the cruise control had a dedicated vacuum source, but you say there's a 'T' on the line. That beats me. The round ball is the cruise vacuum servo/reservoir, as far as I know...

    I suggest getting a copy of FSM from eBay. There's no reason to have one if it's broken, and even if you can't fix it yourself, you can KNOW the problem, and you'll recognize a load of fertilizer when you go to the shop. Fertilizer belongs in the garden.

    A $20 digital camera will help, in MANY ways, for posting pics. Reference at re-assembly, photo-doc'ed work, help from others recognizing hacked work, insurance, etc., etc., etc., ... I have close to 1,000 pics of vehicle innerds and work/cleaning...


  11. #11
    Member hawker4611's Avatar
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    Took your advise and ordered up a notebook style original FSM on Ebay

  12. #12
    Member Schrade's Avatar
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    Quote Originally Posted by hawker4611 View Post
    Took your advise and ordered up a notebook style original FSM on Ebay
    Ummm... notebook style?

    Look like this? BIG red book?

  13. #13
    Member hawker4611's Avatar
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    NO it is Blue and much larger and has CHEVROLET in large white letters
    SERVICE
    MANUAL

  14. #14
    Member Schrade's Avatar
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    Quote Originally Posted by hawker4611 View Post
    NO it is Blue and much larger and has CHEVROLET in large white letters
    SERVICE
    MANUAL
    I'm not familiar with that book. Red book has EVERYthing for vette, for that year. I suggest nothing else.

    Perhaps someone else here knows the blue one...

  15. #15
    Member hawker4611's Avatar
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    Heres a picture of the BlueBook and I also Bought a RedBook

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