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FORD BRONCO -> FUEL SYSTEM; carbs, EFI, pumps, tanks, propane, ... -> Carburetor; Microprocessor Control Unit (MCU) & EEC III
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Air Cleaner Heat Stove Vacuum Motor
Air Cleaner Temperature Sensor (ACTS)
Cold Weather Modulator (CWM)
Feedback Carburetor; Actuator
General Information
Heat Stove
Microprocessor Control Unit (MCU)
Ported Vacuum Switch (PVS) Valve
Temperature Vacuum Switch (TVS)
Thermostatically Controlled Air Cleaner (TCAC)
Throttle Kicker Actuator
V REST Vacuum Restictor/Delay Valve
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Overview; "...The following table lists carburetor ID codes for M-block (351M/400) engines in Ford and Lincoln/Mercury cars.The table is organized by model year and engine application (351M or 400). Unfortunately, I have no information on specific vehicle model applications for these carbs. The following tables list calibration ID codes and Ford service part numbers for Motorcraft 2150 2V carburetors on M-block (351M/400) engines in Ford trucks. Calibration ID codes are similar, and in most cases identical, to carburetor ID codes. These tables are organized by model year and truck model, with a complete table for each model year from 1977 to 1982. Many of these carburetors are still available as brand new, complete assemblies from Ford. However, prices range from $400 to over $800 each. Unless obsolete, you can use the Ford service part number to order one of these carburetors from a Ford dealer parts department. In the case of obsolete carburetors, some of them are still available, either new or rebuilt, from Motorcraft (which can also be ordered by a Ford dealer parts department). See the next section below, Motorcraft replacement carburetors, for more information. The following table lists vehicle applications, calibration ID codes, and Motorcraft part numbers for complete M-block truck carburetor assemblies that are available as Motorcraft OEM replacement parts..." See Tables
Source: by Bubba (Dave R) at via
300 CID, 84-85, Feedback Carbureted Problem Areas; "...This pickup/Bronco application typically suffers from abuse, neglected service and a poorly designed manifold and feedback system. The vehicle will drive tolerably in open loop all the time, suffering from poor driveability and fuel economy (typically in the 8-10 mpg range). Check the mixture control solenoid on the carburetor for a varying duty cycle. A fixed 50 percent duty cycle is the open-loop default value. Check the oxygen sensor for switching (frequency) and amplitude. Verify powers and grounds to the ECU (computer - located inside, above the accelerator pedal). The ECU and 02 sensor grounds are on the firewall in the engine compartment low on the driver's side. Other critical inputs to the computer are the coolant temperature sensor and manifold absolute pressure (MAP) sensor (frequency-based), which both ground ahead and above the battery on the right inner fender well. Manifold leaks are very common (both intake and exhaust). Check all manifold, carburetor mounting and manifold preheat bolts and gaskets for tightness and leaks (flowing propane around gasket areas makes this fairly simple). The exhaust manifold is a relatively thin casting and can be badly warped, particularly if the vehicle has been heavily loaded, used for towing or driven through deep water. A leaking exhaust manifold will dump raw oxygen on the O2 sensor and can make the feedback system attempt to go rich. Carburetor throttle shaft wear is an area for particular attention. Some of the carburetor screws have a propensity for vibrating loose and having the carb literally disassemble itself in normal use. When rebuilding the carburetor pay careful attention to the reassembly of the accelerator pump components -- the washer goes on top of the diaphragm, not below it. This problem has been seen on several remanufactured carburetors as supplied from the rebuilder. Rejetting should be considered a last resort. Air injection switching (upstream, downstream), exhaust system integrity, and catalyst function are areas of common problems on these trucks as well..."
Source: by via
Air Cleaner Temperature Sensor (ACTS) Location & Depiction in Parts Diagram in a 78 400M; "AIR bypass valve” in some Ford technical literature. On some vacuum system diagrams, it is labeled “AIR BPV” or just “BPV.” "
Source: by 78brncoxlt at
Air Temperature Sensor Overview & Specifications in 78-79 351M/400M
Source: by Bubba (Dave R) at via
Choke Pull Off Depiction; The choke pull off opens the choke valve to obtain the proper fuel/air ratio when the engine is cold. - 80.6 MB pdf
Source: by Ford
Choke Thermostat Depiction; The choke thermostat is temperature sensitive and is used to position the choke valve, providing a richer fuel to air ratio when starting a cold engine. - 80.6 MB pdf
Source: by Ford
Conversion to EFI/OBD II & EO4D from a C6 in an 86
Source: by Kurt H at
Dashpot Depiction; The dashpot is mounted on the carburetor and aids in the control of hydrocarbon emissions during deceleration by slowing the closing of the throttle plates. - 80.6 MB pdf
Source: by Ford
Distributor Modulator Valve Depiction; The distributor modulator valve is available in one of three port versions (the illustration is a three port). This valve uses a solenoid to control vacuum air flow. The one port valve is used in the choke-pull down system. The three port valve is used in the throttle kicker system. - 80.6 MB pdf
Source: by Ford
Distributor Modulator Valve Switch Depiction; The distributor modulator valve switch is used in many applications and functions vary by application. This valve switch opens during times of high vacuum and closes during low vacuum. It may be used to dump thermactor air, bleed air to carburetor or perform other functions. - 80.6 MB pdf
Source: by Ford
Distributor Vacuum Control Valve Depiction; The distributor control valves listed in this catalog may be either the Type 1 or Type 2 as illustrated. These valves control vacuum to the distributor affecting spark advance. - 80.6 MB pdf
Source: by Ford
EEC III Feedback Carburetor System Diagram
Source: by Tommy at
EEC III Testing, Pin-Out, Wiring & Vacuum Diagrams in an 82; "...Woe was me, when I found out my 82 Ford Bronco was an EEC 3..."
Source: by Tommy at
EFI Swap to Carburetor
Source: by BLADE262US, Seabronc & Justshootme84 via miesk5 at Ford Bronco Zone Forums
EFI Swap to Carburetor
Source: by members at Ford Bronco Zone Forums
EFI Swap to Carburetor; "...It's actually a pretty simple swap. Basically all of the computer/sensor stuff can be scrapped. You won't need any of it. What you will need...a carb (obviously), a new intake manifold, a new distributor, an ignition control box (like an MSD or Mallory box...I've had good luck with MSD 6A boxes so long as they're not exposed to significant heat), and a carb fuel pump. The EFI pump is way too strong for a carb so you'll need something like a Holley carb electric pump. The ignition stuff is pretty straight forward, but for a working tach you'll need to find the tach wire in the ignition wiring harness and attach it to the positive side of your coil. I know in Mustangs this wire was green with a yellow tracer. It may be the same in your Bronco, but it's good to double check. For a carb I would use something like a Holley 600cfm double pumper or a slightly smaller Carter carb. I had a 625cfm Carter on my Mustang before I switched over to a turbo'ed EFI setup and it was a little too much for the motor. One point worth stating is that if you have an automatic transmission that has overdrive (like an AOD), you'll need an adapter for the TV linkage on the transmission since AODs never came on carbed motors. One is (or at least used to be) available for Holley carbs through Sacramento Mustang, but they retail for just under $100. If you have a 3 speed like a C4 then all you'll need to do is make sure the carb has a kickdown linkage. Mind you I got my old Carter to work with my AOD...but I think that was just sheer luck. Hope this helps...let me know if there's anything else I can clear up for you..."
Source: by Steve at
EFI to Swap to Carb in a 90 Mustang LX from a 5.0 to 5.8
Source: by 85_SS_302_Coupe at
Electrical Symbols in an 86 from Electrical and Vacuum Troubleshooting Manual (EVTM) Partial
Source: by Ford via Chris B (Blue, bronco boy) at
Emission Vacuum Diagram in a 78 351M
Source: by 78brncoxlt at
Emission Vacuum Diagram in a 78 351M
Source: by 78brncoxlt at
Emissions Failures, Diagnosis Tech Tips (high CO, O, CO2, etc.)
Source: by via
Evaporative System Overview, Testing, Part Numbers & Diagrams in an 85 351W; Carbon Canister, Vapor Separator, Fill (gas) Cap, Vapor Line, Vacuum Vent valve, Fuel Tank Vapor Separator/Rollover Valve Assembly, Carburetor Fuel Bowl Thermal Vent Valve, etc.
Source: by Chilton via miesk5 at FSB
Feedback Actuator Motor Depiction; The actuator is part of the feedback control system on certain carburetors. The actuator is threaded into the carburetor body and its shaft moves a fuel metering pintle valve to produce a richer or leaner air/fuel mixture in response to signals from the EEC or MCU systems. - 80.6 MB pdf
Source: by Ford
Feedback Carburetor Test
Source: by
Feedback Control Solenoid Depiction; The feedback control solenoid is a pulsing solenoid that introduces fresh air from the air cleaner into the idle and main system vacuum passages. A signal from the ECA activates the solenoid. - 80.6 MB pdf
Source: by Ford
Feedback Overview; see page 37 in Ford EEC IV Operation & Testing Overview; PowerPoint Presentation
Source: by Ryan M (Fireguy50) at
Float Bowl Vent Solenoid Valve Depiction; "...This solenoid valve is part of the evaporative Emission Control System and is a normally open valve located in the fuel bowl vent line. The valve closes off the fuel bowl vent line when the engine is running, and returns to the open condition when the ignition is turned off, allowing fuel vapors to flow to the carbon canister..." - 80.6 MB pdf
Source: by Ford
Fuel Bowl Vent Valve Depiction; "...The vent valve is a temperature actuated valve inserted in the carburetor-tocanister vent line. This valve is closed when the engine compartment is cold preventing fuel tank vapors from being vented through the carburetor fuel bowl, forcing them instead into the carbon canister..." - 80.6 MB pdf
Source: by Ford
Hot Idle Compensator Depiction; "...The compensator may be internal or external to the carburetor and is used to cool the engine during extreme hot engine idle operation. When open, the compensator bleeds air into the manifold, which leans out the fuel/air ratio at idle. The increased air causes an increase in engine idle speed, which results in cooling of the engine..." - 80.6 MB pdf
Source: by Ford
Idle Tracking Switch Depiction; The idle tracking switch is a mechanically operated electrical switch mounted near the throttle linkage on certain carburetors. Uniterrupted or prolonged deceleration is detected by the switch which sends a signal to the MCU to change the vehicles carburetion and thermactor air. - 80.6 MB pdf
Source: by Ford
Microprocessor Control Unit (MCU) Overview; "...The Microprocessor Control Unit (MCU) system was used on most 1981–83 carburetor equipped vehicles, and 1984 and newer V8 engines with feedback carburetors. The MCU system uses a large six sided connector, identical to the one used with EEC-IV systems. The MCU system does NOT use the small single wire connector, like the EEC-IV system. This system has limited ability to diagnose a malfunction within itself. Through the use of trouble codes, the system will indicate where to test. When an analog voltmeter or special tester is connected to the diagnostic link connector and the system is triggered, the self-test simulates a variety of engine operating conditions and evaluates all the responses received from the various MCU components, so any abnormal operating conditions can be detected.Diagnosis of a driveability problem requires attention to detail and following the diagnostic procedures in the correct order. Resist the temptation to begin extensive testing before completing the preliminary diagnostic steps. The preliminary or visual inspection must be completed in detail before diagnosis begins. In many cases this will shorten diagnostic time and often cure the problem without electronic testing..." READ MORE for Reading Codes & Diagnostic Trouble Codes (DTC's)
Source: by Ford via
Throttle Emission Control Solenoid Depiction; The throttle emission control solenoid is carburetor mounted and provides a stop for the throttle lever when the ignition is on. When the ignition is turned off, the plunger retracts to allow the throttle valves to close, preventing engine dieseling. - 80.6 MB pdf
Source: by Ford
Tuning with a Vacuum Gauge
Source: by
V REST on 78/79 & early 80s is a Vacuum Restictor/Delay Valve, it delays 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; READ MORE
Source: by miesk5 at FSB
Vacuum Gauge Diagnosis
Source: by
Vacuum Gauge Diagnosis - BEST!; Normal engine; Steady gauge 18"-20" at all speeds..." READ MUCH MORE
Source: by Craig U at
Vacuum Leak Symptoms, General; "...Too fast an idle speed; A rough idle or stalling; Hesitation or misfiring when accelerating; An idle mixture that defies adjustment (carburetor)
Source: by
Vacuum Line Routing Diagram in a 79 351M
Source: by Steve S at
Wiring Diagram in 78 Bronco & 76-78 F Series
Source: by Blue79 at
Wiring Diagram in a 79
Source: by Chilton
Wiring Diagram in an 81 F 150
Source: by Chilton via miesk5 at FSB
Wiring Diagram in an 84
Source: by
Wiring Diagrams in an 86 Bronco & Ford truck; w/Many Diesel Engine Systems & Components
Source: by Agnem (The Moosestang) at