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980 Posts
Discussion Starter #1
I know the vacuum canister is a necessary part of the vacuum system but what I want to know is if it has to be as big as the one on my 96 351 Bronco? Can I use a smaller one? Why is there two hoses coming out of it??

Super Moderator
26,998 Posts
yo GARY,
You need it
The Vacuum Reservoir (coffee can) stores vacuum & prevents rapid fluctuations or sudden drops in a vacuum signal such as those seen during acceleration.
One hose to Intake Manifold Tree (on top of plenum, driver's side) see pic of the tree by joelb23
other to a check valve and onto VMV, EGR/EVR, TAB, TAD etc.

You can get some from other Fords or GMs that are smaller and place two or more in another location, should be = volumes as OEM tank though

Overview; "...The vacuum is an energy that is used as a power source to operate different emission controls and accessories like the controls for the ventilation system. There are times that an engine does not create a good supply of vacuum. Because of this the vehicle manufacturers install reservoirs to store vacuum. The hose from the engine or the reservoir itself will have a check valve that blocks the loss of vacuum back to the engine. Why is this? When accelerating, the amount of vacuum created by the engine drops to a level that will no longer power any emission controls or provide for control of the ventilation system. The reservoir is designed to hold enough vacuum in storage to maintain control under most driving conditions. If the check valve fails the vacuum reservoir will lose vacuum so quickly that there will be none left in reserve. The result? A loss of control of vacuum operated devices.You can make your own as SigEp did but for the Emission stuff..."
Source: by miesk5 at FSB

See your Emission Vac Diagram on your Vehicle Emission Control Information (VECI) Decal;

Or if missing and you need Emission, PCM, etc Ford part numbers get it On-Line for Free at Ford.
Click "Quick Guides" in left panel;
Scroll to & CLICK VECI Labels "Provides Vehicle Emission Control Information (VECI) and a related calibration parts list." Enter applicable info (need to know your Calibration number from your B-pillar sticker).
Vacuum Diagram is the same as the one on the core support or hood or air filter cover.
Suggest Right Clicking this Hot Link & Open in New Window
Source: by Ford @

Vacuum Line Acronyms & Color Codes
Source: by Steve83 (Steve, That dirty old truck) & Seabronc (Rosie, Fred W) at FSB
have been working on this off and on for awhile and have combined Steve, Seattle FSB and Fred's info with mine;

Vacuum Line Acronyms & Color Codes;
Red = Main vacuum;
Green = EGR function;
Orange = Heat control Valve (exhaust & intake) (AKA heat riser but more complex);
Yellow = from the TAD Solenoid (driver's side Forward Solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold (Distributor Advance in Carbureted Engines);
White = EGR vacuum (source);
Black = Mainly used for the Evaporative emissions control;
Black = Thermactor ACV or Diverter valve;
Blue = Throttle Kicker control;
Pink = from the TAB Solenoid (driver's side rear solenoid) to the bottom of the Thermactor Air Bypass Valve (TAB or BPV/AIR Bypass (AIRB) valve); ACV (Air Control Valve) is the TAD (Thermactor Air Diverter) Valve (AIR Bypass (AIRB) and AIR Diverter (AIRD) valve combinations);
MAN VAC is Manifold Vacuum;
FPR is Fuel Pressure Regulator;
EGR is Exhaust Gas Re-circulation Valve
SOL V: Thermactor Air Diverter (TAD) Solenoid (SOL V) (AIRD) & Thermactor Air Bypass (TAB) Solenoid;
EVR is EGR Vacuum Regulator;
VRESER is the Vacuum Reservoir Can (Tank);
V REST on later years is Vapor Valve (Roll-Over @ Gas tank);
V REST on earlier years such as 78/79 & SEABRONC's 83 is a Vacuum Restictor/Delay Valve, it restricts vacuum for a certain amount of time, on most engines a vacuum line from the carburetor base runs to a T & then to V REST to the distributor; Carbon Can is Carbon Canister (Charcoal Canister, Vapor Canister, Evaporative Emission (EVAP) Canister);
MAP is Manifold Absolute Pressure Sensor;
AIR BPV is the AIR Bypass (AIRB) Valve, also called the TAB (Thermactor Air Bypass) Valve;
CPRV is Canister Purge Solenoid Valve/ Canister Purge Solenoid (CANP);
VCKV is Vacuum Check Valve;
CAT is catalytic converter;
ENG is engine;
PCV is Positive Crankcase Ventilation Valve.

HVAC in 92-96;
Black = from engine source (tree) to vacuum check valve & to vacuum reservoir tank & to Control Panel;
White = actuates the Outside/Recirc air door two-position vacuum control motor;
Blue = Mix (actuates the FLOOR/PANEL air door two-position vacuum control motor);
Red = Floor Flow & Yellow = Panel, (actuate the FLOOR/DEFROST three-position air vacuum control motor).

Also, da vacuum tank for the heater or heater/air conditioning controls is sonically welded to the side of the heater or evaporator case. If a vacuum leak occurs at the vacuum tank, a different vacuum tank can be used to make the repair without removing the old vacuum tank.

HVAC Vacuum Diagram in 92-96; "...80-91 similar, except 87-early 88 w/factory air; The 80-86 vacuum tank is a plastic ball on the R wheelwell..."

Source: by Steve83 (Steve, That dirty old truck) at

980 Posts
Discussion Starter #3
Thanks miesk...good information!! always!

Super Moderator
26,998 Posts
btw, make your own from whatever or get some slick looking small cannisters @ JEGs, adv auto etc.

The JEGS vacuum canister gives you an extra shot of vacuum that the new cam won't allow you to have in order to feed your power brakes. Durable 5" x 7" canister will not flex under load and includes mounting bracket, one way check valve, grommet, 90º fitting and port plug. Available in a black wrinkle finish steel or an extruded billet aluminum canister. The aluminum canister features billet end caps, for a sanitary appearance, and a clear anodize or polished finish with a matching check valve cover. Also includes the "Just-A-Ble" integral mounting system, exclusively from JEGS, for easy attachment with stainless hardware. Liquid filled pressure gauges available separately. Replacement check valves (sold separately) are an ideal dress up item for power brake boosters

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