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Thread: My new 78 Grand Marquis vacuum help PLEASE........

  1. #1
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    Default My new 78 Grand Marquis vacuum help PLEASE........

    Question.... My 78 Mercury grand Marquis has the 400. I'm removing all the smog shit, there are 3 ported vacuum switches, one is in the water pump and the other two are in the water neck......there is a shitload of vacuum spaghetti that goes to all three obviously.... Which ones can be removed and not needed anymore..... Smog pump and all its crap is gone, egr is still there Anyone have a vacuum diagram for the 78 400
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  2. #2

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    You can get rid of 99% of that crap!
    A vacuum diagram can be found online.
    But you have other things holding back the power and the MPG's
    The distributor advance will be need work and the timing chain will be retarded.
    The EGR needs to go.
    And the carb will need different jets.
    Dual exhaust, get rid of the cats.
    You can get a lot more out of a 400, but you'll have to go into the engine.
    And I'll bet the gear ratio in the rear is nothing to brag about.

  3. #3
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    Cats gone, duals on.... Keeping the egr, smog pump gone so far, but I have 3 ported vac switches and which one or ones are critical, I can't find a diagram of vac hoses

  4. #4
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    Here's where I'm at
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    Quote Originally Posted by mcninetyone View Post
    I'll bet the gear ratio in the rear is nothing to brag about.
    My '79 has a 2:47 gear ratio.
    '79 Continental Town Car
    '90 Crown Victoria LTD
    '94 Crown Victoria

  6. #6

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    I haven't done a 78 MGM but I did help restore a 73 Mustang with a 351C. It had that ported vacuum switch on the upper hose inlet. We plugged the holes on the inlet, and followed the vacuum hoses to their source and plugged them off. I assume the 78 crap will be a lot more complicated than the 73 crap on the Mustang.

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    GMN Regular DerekTheGreat's Avatar
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    Nice sled man. I love those dished wheels.
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

  8. #8
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    Egr still needs vacuum - it's probably hooked up to one of those thermal vacuum ports to keep it off while the engine is cold. Trans needs it vacuum modulator as well. Of course power brakes need vacuum also. If you have cruise control, that should remain intact. And your HVAC still needs vacuum. Last barge I had also needed it for hideaway headlights. So you'll need to keep some of the spaghetti.
    1988 Crown Vic Wagon - daily
    1990 Country Squire - weekend cruiser, former lawn ornament
    Other: 95 Ranger, 74 F250, 68 Mustang, 94 Mustang
    Sold: 1982 LTD and 1987 Crown Vic

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