Hello . Need A vacuum diagram for 1978 Mercury Grand Marquis with 400 engine . Can you help? No luck finding anything so far.

Question edited for a lot of clarity.
Question moved from MISC to correct category.

https://www.google.com/search?q=1991+Mercury+Grand+Marquis+GS+5.0.+Vacuum+hose+diagram&rlz=1C1QJDB_enCA643CA644&sxsrf=ALiCzsbNrlH1W5VV0OAK4h8jTsQrUJYYeQ:1662518015156&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjzjued0oH6AhWShYkEHWqvAisQ_AUoAXoECAEQAw&biw=1920&bih=937&dpr=1

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A little confusing I found 3 fuse box diagrams which cover your car. Not sure but hope it helps.

Mercury Grand Marquis (1998 - 2002) - fuse box diagram
https://www.autogenius.info/mercury-grand-marquis-third-generation-1998-2002-fuse-box-diagram/

Mercury Grand Marquis Third Generation (1998 - 2002) - fuse box diagram
https://www.autogenius.info/mercury-grand-marquis-third-generation-1998-2002-fuse-box-diagram-2/

Mercury Grand Marquis Fourth Generation (2002 - 2011) - fuse box diagram
https://www.autogenius.info/mercury-grand-marquis-fourth-generation-2002-2011-fuse-box-diagram/

The vacuum line diagram is under the hood on the federal emissions decal. Any other vacuum related diagrams are in the Ford electrical and vacuum troubleshooting booklet. You can buy these used on eBay for less than $20.00 US

You can get free diagrams at www.bbbind.com/ . home page click on technical information ,the click on tsb's an free wiring diagrams . On the next page go to the bottom an click i agree . Next page click wiring diagrams then enter your vehicle info . year ,make , mode ,engine size. under system click electric distribution . Subsystem fuse panel . Good luck .

Here'a link to your vacuum diagram Doug.

Try looking here. Good Luck!
www.gobookee.net/2004-grand-marquis-radio-wire-diagram/

Orielly auto parts or Auto zone should have a repair manual for that car. They go for about $25.00. The manuals have vacuum diagrams.

HERE can find this diagram and description about fuses and fuse box locations: Mercury-Grand-Marquis-Owners-Manual

Hope helps (remember rated and comment this).

1998 Mercury Grand Marquis
4.6 liter V-8 VIN "W"



I will get you the rest of the info in just a few hours...I am at work!

hi,

make sure your vacuum advance doesent have a slow leak, attach a spare piece of vac hose to the vac advance mod on the distrributor and s u c k on that hose., it should hold air and not leak make sure you dont have any other vacuum leaks. the vac mod on the tranny could have the same problem. open the jets on the carb a little by turning counterclockwise, you see the engine mellow out. theres two screws up under the front of the carb might need a rebuild, fuel filter could be half clogged. and then re time the engine..

jm