Vacuum lines
Thread Starter
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Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
Likes: 78
From: NE Texas
Vacuum lines
Have two lines flopping around loose on an essentially stock 300cid 1978 with C6 transmission. Both have those disc-like whatever-they ares in the middle.
1) One seems to be hooked to the furthest right port on the carbon cannister.
2) On the valve cover at the rear there is a two-port 'tree' sticking up with two lines atached. The thin line is connected, the fatter line appears like it would attache somewhere near the carb but I can't find an open port.
I have looked at several vacuum diagrams and none seem to match mine.
Second set of questions - I am tempted to remove/cap all the vacuum lines except those going to the brake booster, transmission, and vacuum advance. Would that a) affect performance either way and b) what changes in tune should I make?
1) One seems to be hooked to the furthest right port on the carbon cannister.
2) On the valve cover at the rear there is a two-port 'tree' sticking up with two lines atached. The thin line is connected, the fatter line appears like it would attache somewhere near the carb but I can't find an open port.
I have looked at several vacuum diagrams and none seem to match mine.
Second set of questions - I am tempted to remove/cap all the vacuum lines except those going to the brake booster, transmission, and vacuum advance. Would that a) affect performance either way and b) what changes in tune should I make?
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Normally the Ford engineers used the vacuum system to meet emission requirements and to make the engine run its very best. When one alters this system, it usually requires making other adjustments.
Does your engine have EGR? If it is deleted or blocked off, it is not unusual for the engine to begin pinging when under a load. The timing will have to be retarded [will decrease power and gas mileage] or the distributor will need to be re-curved.
A vacuum line should go to the thermo valve in the air cleaner housing and from there to the snorkel of the air cleaner. The valve senses the inlet temperature and opens and closes a flapper in the snorkel. The flapper directs the incoming air, between cool air and hot [exhaust heated] so the air going into the carburetor will remain within a specific range [~105F]. This helps prevent carburetor icing on cool damp starts.
If you can post several close-up photos of your engine, others will better be able to assist you.
Does your engine have EGR? If it is deleted or blocked off, it is not unusual for the engine to begin pinging when under a load. The timing will have to be retarded [will decrease power and gas mileage] or the distributor will need to be re-curved.
A vacuum line should go to the thermo valve in the air cleaner housing and from there to the snorkel of the air cleaner. The valve senses the inlet temperature and opens and closes a flapper in the snorkel. The flapper directs the incoming air, between cool air and hot [exhaust heated] so the air going into the carburetor will remain within a specific range [~105F]. This helps prevent carburetor icing on cool damp starts.
If you can post several close-up photos of your engine, others will better be able to assist you.
Thread Starter
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Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
Likes: 78
From: NE Texas
No pinging, engine seems to run fine (other than occasional brief run-on when the engine is shut down), mileage is steady (albeit poor around town, not a shock with a 2.8 diff). The vacuum lines, other than the two I mentioned, are ALL hooked up, and have been checked for leaks or splits. I drive with a pretty light foot but when on occasion I have hit the gas the engine responds without bogging or hesitation. If having everything hooked up correctly costs me no performance, I'm all over that - if I can get a measurable boost by disconnecting many of the lines, I'm happy with that too. I'm just **** retentive enough to want to know where the hell these two (currently plugged) loose lines go!
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Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
Likes: 78
From: NE Texas
been a bit distracted, sorry - Hope I am doing this right!
First image looks down on the carbon cannister, that outboard hose with the red arrow pointing to it is about two feet long and has a round valve-looking thing in it a few inches from the open end. It looks long enough to terminate at the back side of the carb but I can't find any open ports.
The other line is longer, and comes from the circled device in the valve cover in the other pic just back of the air cleaner on the valve cover. It also has a round valve-looking device partway along... it looks like it should terminate on the front of the carb or EGR, but again, no port appears open. You can actually see its open end in the first picture just above the blue cable cover on the left side of the first pic. I would almost wonder if they should somehow connect to each other, but as you can see in the pic where they are next to each other, they are different sizes and IDs. Both lines are currently plugged to be safe. Any help would be appreciated!
First image looks down on the carbon cannister, that outboard hose with the red arrow pointing to it is about two feet long and has a round valve-looking thing in it a few inches from the open end. It looks long enough to terminate at the back side of the carb but I can't find any open ports.
The other line is longer, and comes from the circled device in the valve cover in the other pic just back of the air cleaner on the valve cover. It also has a round valve-looking device partway along... it looks like it should terminate on the front of the carb or EGR, but again, no port appears open. You can actually see its open end in the first picture just above the blue cable cover on the left side of the first pic. I would almost wonder if they should somehow connect to each other, but as you can see in the pic where they are next to each other, they are different sizes and IDs. Both lines are currently plugged to be safe. Any help would be appreciated!
Thread Starter
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Fleet Mechanic
Joined: Sep 2014
Posts: 1,626
Likes: 78
From: NE Texas
As I mentioned in my first post - I don't see ANY open ports. There is what appears to be a capped off one on the top inboard area of the 1 barrel carb on the same side as the gas line, but there appear to be no other potential sites - hence my request. I am hoping someone can say "I have a 300 of the same vintage and that vacuum cannister line connects to X spot and that PCV valve line hooks onto Y right by >>>". Not trying top be dense, I have just been over this thing multiple times and my problem is that there appears to be NOI spots they can plug to - and as you can see by the photos, my engine is pretty clean and stock. Should be easy to find, but aren't. Thanks!
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Senior User
Joined: Mar 2007
Posts: 481
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From: Deep River, CT.
This is a stab in the dark and not sure if done in 78.
Ford would put vacuum line routing decals under the hood some where for the vehicle. Wondering if there is a site that would list various decal schematics out there. I think I used to see them in Motors Truck Repair Manuals.
Ford would put vacuum line routing decals under the hood some where for the vehicle. Wondering if there is a site that would list various decal schematics out there. I think I used to see them in Motors Truck Repair Manuals.
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Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
Contact WillieJoe62. He has a thread regarding the restoration of a 1981 [I think] and he went into great detail and maintained originality. He may be your best bet and has wonderful photos. I will PM him and ask for his assistance.
Posting Guru
Joined: Feb 2012
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From: Rocky Mountain High
July will mark 30 years since I stepped out of the ranks. I was at Ft. Lewis, Ft. Campbell, and Berlin, and a lot of interesting places in between.
First is the PCV hose, connects to the base of the carb on the right rear. Hose highlighted in green (obviously).
I know plenty of guys have capped off all these lines, but they're there for a reason, and Festus has run great with everything attached.
First is the PCV hose, connects to the base of the carb on the right rear. Hose highlighted in green (obviously).
I know plenty of guys have capped off all these lines, but they're there for a reason, and Festus has run great with everything attached.