Thanks for the post. I think I'm using the wrong technical terminology about the Carter YFA carburetor on my 1984 Bronco. I think the correct terminology is most likely "Feedback" carburetor. Below I've pasted some information I found surfing the web today while trying to figure out a fix for my Bronco. All I want to do is get rid of all that "crap". I could care less what the correct terminology of this crap is called, ECU (Engine Control Module) Oxygen sensor, air injection, mixture control solenoid, open loop, closed loop, MAP sensor, or CTS. I'd like to think, maybe a carter YF carburetor, instead of the carter YFA, might work for me. I could use some assistance finding the year <nobr>pickup
</nobr> / Bronco that has just a plain old YF on an inline 300 6 cylinder. Any ideas? [img]images/graemlins/cool.gif[/img]
</nobr> 300 CID 6-cylinder, 1984-1985, feedback, carbureted
This pickup/Bronco application typically suffers from abuse, neglected service and a poorly designed manifold and feedback system. The <nobr>vehicle
</nobr> 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 <nobr>trucks
</nobr> as well.