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Thread: EFI to Carb vacuum questions

  1. #1

    Default EFI to Carb vacuum questions

    Hello,

    This is a project im working on to make a daily driver, right now it's a rolling shell that is getting a mildly built 302 and a T5. Since the wiring harness is shot, and most of the related sensors gone, I figured it would be easier and cheaper to make it carbureted. How would I route the vacuum to keep everything working besides the brake booster. Could I just go off the haynes diagram for the 351w grand marq and replicate that system?

  2. #2

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    I'd start with looking at the 1979 vacuum diagrams.

    You didn't mention what year the car is. You'll definitely need a line to the HVAC controls. If you want to plumb in cruise control, that will need a line to the actuator and a dump line to the brake and clutch pedals.
    If you keep the charcoal canister (which you should: it will keep the car from smelling like gas and dripping gas out the tank vents) you'll want to plumb that to the carb.
    You may need a line for a vacuum advance, depending on your distributor choice.
    You may need a line for EGR if you keep it (a properly working EGR helps with fuel mileage and emissions at part throttle; it also reduces the load on your catalytic converters at part throttle); the EGR system is more complex on a carb'ed car so I imagine that you won't bother with it.

    The 351 Grand Marq had a few different carbs over the years. The later ones were Variable Venturi carbs which worked with an EEC controller and were way more complex than what you're doing.

    Most importantly, make sure what you're doing is legal in your state. It would suck to build this car and have to go back and add something you removed before you can put it on the road.

  3. #3

    Default

    It is from 1988 and had the eec-iv system. I do intend on keeping hvac and all smog/emissions equipment functional. Cruise control will be disabled though. I always check with local and state laws to see what hurdles Ill have to dance around, and its understandable as to why. Thankfully the commonwealth only really cares if its not falling apart and has its emissions equipment.
    Man it really might be simpler to stay with efi for now..

  4. #4
    Lost and driftin' Arquemann's Avatar
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    This thread sparked my interest aswell, since I've thinking about swapping out my CFI. I'm keeping my slushbox though.
    Though I do not intend to keep the Thermactor and probably can't keep the EGR if I go with a 4bbl.
    Cruise I'd like to keep but it has to be fixed first. Is the cruise system any way linked / a part of the EEC-IV engine management? Does it function as a separate entity?

    So I've got to plumb HVAC, charcoal system, brakes, distributor, PCV, cruise and what else? Charcoal system can probably stay quite stock.
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

  5. #5

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    I'm not so familiar with the CFI, but the EEC-IV is really not a bad system when it's working. If the repairs to the EEC-IV setup aren't too extensive, I wouldn't muck about with a carb. Then again, you're dropping in a whole new engine, so it's a matter of what you're comfortable with. On the '88, there's not too many things you'd lose by pulling the computer (Tripminder, if you have it, won't work with a carb...unless you have a very uncommon fuel flow meter in your box of goodies).

    Swapping to a 4-bbl with EGR will require an intake with an EGR spacer under the carb, and various temperature/vacuum switches.

    Cruise is a standalone on most Fords at least through the late 80s, and even some into the late 90s. Definitely on your CFI car. You'll just need to hook the line from your vacuum canister to someplace on the manifold.

  6. #6

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    Diagnosing and repairs on the eec-iv can be a headache.. I've either had easy repairs that take at most an hour to perform, or absolute ballbusters that take more than a week just to diagnose and follow a trail of issues. They are very simple systems but can be very fussy if things aren't within it's parameters. However Ive heard converting from map to maf can make mods and tunes much easier to deal with. Honestly Id much rather go with a carb, if anything shits the bed I can at least get down the road.

  7. #7
    Lost and driftin' Arquemann's Avatar
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    Yeah, I have a long list of stuff that's been done to mine. It was at a shop for a month after I got lost. Still has the original issue...

    The main temptation in going carb is the simplicity, shit just works. And if it doesn't, it's simple to diagnose and fix. Also pretty much nothing CFI/SEFI related is in stock here in Finland.
    Last edited by Arquemann; 01-16-2020 at 01:13 PM.
    1985 Mercury Grand Marquis LS
    1997 Volvo 850 GLE Estate

  8. #8

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    Yeesh, finding cfi parts in Finland must be as hard as trying to find non-GM SAAB parts in the us

  9. #9
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    When i did my carb conversion on my 84 i removed everything. It only needs three lines to run right. Main vac line from the intake to the vac manifold on the firewall that goes into the cabin, you need one to the booster, and one from the ported vac signal on the carb to the vac advance on the distributor. Swap the ignition to a DurasparkII.
    Last edited by JeffBoudah; 01-16-2020 at 05:00 PM.

  10. #10
    I'm an air-conditioned gypsy gadget73's Avatar
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    You can't keep the smog and emissions stuff without the ECM. It runs entirely from the computer. If you're putting a carb on an 88, you may as well de-smog it because its just useless weight at that point.

    we're not going to even discuss the pre-ECM smog bullshit, because fuck that mess.

    86 Lincoln Town Car (Galactica).
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    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

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  11. #11
    Beater gonna beat sly's Avatar
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    Quote Originally Posted by gadget73 View Post
    we're not going to even discuss the pre-ECM smog bullshit, because fuck that mess.
    This. So much this.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
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    Quote Originally Posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
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