Yo M,
Here is info that I have collected;
Single-Function Reservoir Disassembly; "....More then likely you'll need to remove the transfer case skid plate for more working room BUT you CAN get the bottom part to unscrew if you use the right tool to get it tight enough and have leverage to loosen it PITA that it is. There's probably a lot of built up road grit in and around the threading so use some PB Blaster etc. Think out of the box on this one and get creative with a tool ...but there's no need to remove the top part. The top part (cap) of the reservior has these little spring loaded pressure valves on each side where the lines go to inside to keep the reservior full, the bottom half threads are similar to "pipe" threads so they're tappered for a tight seal so it does take a bit of energy to get it free.....BECAREFULL because it's plastic and if you break any part of it you won't be able to drive the BKO. The O ring can be a PITA also just read above and work at it carefully..."
Source: by JKossarides ("The Bronco", Jean )
Single-Function Reservoir in 84-89; "...The PN for the filter is given, but you shouldn't actually have a filter in there. It should be an external inline filter further up the frame rail - you only buy the reservoir filter to get the O-ring, and only then if you have some reason to open the reservoir bowl. Unless you're having fuel delivery problems that you've isolated to the reservoir, you should never open it..." Miesk5 NOTE; Steve deleted his posts here in the Zone.
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Single-Function Reservoir O Ring; "The Ford engineering number on the filter is E6TZ-9365-A. A reservoir marked "DO NOT REMOVE CUP" does not contain a filter. For a replacement O-ring for the cup, buy a NAPA 3268 (or equivalent) filter..."
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88 Single-Function Reservoir
Used on '88-89 Broncos & F-series/E-series/Rangers/others with single tank dual-pump EFI. In this version, the only moving part is the tank-side inlet check valve. The return ports flow freely and are NOT connected to the reservoir. The engine-side supply port is open to the reservoir.
To test it, unplug the frame fuel pump, disconnect the engine-side supply (large) line, and cycle the key. If fuel flows out of the reservoir ******, the reservoir is working normally. If not, disconnect the tank-side supply (large) line, and cycle the key. If fuel flows out of the line, the reservoir check valve is probably stuck, or its internal filter is clogged.
A reservoir marked "DO NOT REMOVE CUP" does not contain a filter.
For a replacement O-ring for the cup, buy a NAPA 3268, Fram CG3862, or equivalent filter.
To permanently eliminate the reservoir, use these Dorman fuel tubes.
http://www.dormanproducts.com/p-12461-800-159.aspx
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88-91 Single-Function Reservoir (SFR) Fuel Flow
Fuel flows in through the larger tank-side supply ****** from the in-tank pump to the inlet check valve, which allows it into the reservoir. As the cup fills, fuel moves up the pickup tube & out the larger engine-side supply ******. Unused fuel enters the engine-side return ******, bypasses the blocked-off check valve ('88 revision) and exits the tank-side return ******.
The only fault that would cause a noticeable problem would be for the check valve to stick closed, blocking any fuel from entering the reservoir, but this isn't likely. With the cup removed (have a replacement cup O-ring in-hand before attempting), a sharp pick can be used to pull the valve downward & open. The valve cannot be removed from the reservoir body.
Source: by Steve, @ Ford Bronco Zone Forums
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I have never worked on these reservoirs.