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FORD BRONCO -> EXHAUST; headers, mufflers, X & Y pipes, sound clips... -> Leak
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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
BBK header misfit info & pics in a 92
Source: by topfisherman at
DTC P0420 Catalyst System Efficiency below Threshold (Bank 1); Symptoms, Causes & Possible Solutions; Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
Source: by
Exhaust Sound, Air injection Tube
Source: by
Gasket; "...factory manifolds do not use a gasket..."
Source: by justshootme84 (Randy Z, Casual Mudder) at Ford Bronco Zone Forums