BB 512i Fuel Problems

No, the total BB512i OM fuel capacity is given as 24.2 gallons of which 3.3 gallons is considered the reserve -- so 20.9 gallons usable before you are into the reserve. (Ferrari listed this in a confusing way in the OM, and people often wrongly add the 3.3 to the 24.2, but that's not what Ferrari meant.)

No, you have two CIS fuel pumps -- the terminals for the fuel pump fuses are a known trouble area that overheat (from I^2*R heating) and get melted/burned up (e.g., they can work OKish for a while from cold start-up, but then overheat and start not making good contact). Definitely something to check/inspect. Your report of bad running with still a relatively lot of fuel remaining is not a normal thing (but could be something else, too).

 

Also, check the fuel filters.

 

You said 15 gallons for the gauge to read full. Was the tank indeed full?

I replace bad fuel senders fairly regularly. It may have really been out of gas.

 

Do not forget that there are two type of filters : the filter (ref 113977) after the pump(s) that is usually properly serviced, and a filter (ref 116404) within the tank that is usually as old as the car itself. This later filter is basically a mesh screen that protects the fuel pickup and prevent the crude to be swallowed by the pumps.

The issue here is that if the in-tank filter is gone, the pumps do have to cope with all the crude and may starve the engine. The engine is still protected from the crude because the dirt will be captured by the thin filter which is located after the pump. The pumps however do have to cope with it which will have an impact on amp-draw (failure of the relay/fuse board) and reduced flow.

Finally, as you do have twin fuel distributor you should (?) have twice of everything (i.e two tank filters, two pumps, two filters, two accumulators). On the diagram https://www.eurospares.co.uk/parts/ferrari/512-bbi/fuel-system/fuel-tanks-pumps-and-pipes-39395, one can clearly see the two filters in the tanks.

 

That SPC figure is what is misleading the OP -- for simplicity, they only show 1 pump, 1 accumulator, and 1 filter (those same components that are downstream of the RH tank filter are omitted to reduce clutter in the figure), but the quantity needed of each is listed as "2" in the parts table.

 

Quite easy actually: you just have to disconnect the return fuel line that gets out of the fuel distributor and sends the excess fuel to the tank. You also have to disconnect the safety switch of the distributor (both distributors do have green plugs, one is connected to a cable that you have to remove).

Once the safety switch is disconnected the pumps will work, no matter the engine is running or not. As the engine is not running all the fuel pushed by the pump should get back to the tanks (i.e through the return line that you have disconnected). You then have to validate that the flow is approximatively 8l / 30s (on each distributors).

You want to check the return line as this ensures that the fuel can pass through the fuel pressure regulator, so the pump is "under load".

 

I can’t be of help with your issue, but hope you get it sorted in short order! Out of curiosity @John Peterson is your BBI the same car that RPM Vermont had videos of on their YouTube channel?

 

Even though the stock in-tank BBi filter is not available, you should still have a coarse filter between the tank and the fuel pump inlet. This thread shows a very well made DIY metal screen filter added to the TR stock metal fitting, but others have also just wired a "sock" type filter element onto the stock metal fitting:

https://www.ferrarichat.com/forum/threads/tr-in-tank-fuel-filter.602459

Another option might be to put an inline filter in the rubber hose between the (now filterless) stock metal fitting and the fuel pump inlet (although can't say that I've ever seen one for such a large diameter hose, but I haven't looked for one either). The "roller" style pump head on the CIS fuel pumps is very intolerant to passing any hard debris.

This pic shows how another BBi FChatter added an aftermarket filter sock to his old fittings (but I'd use a piece of metal wire to secure to the fitting it rather than a plastic zip-tie and maybe make a sort of wire metal cage to put inside the sock to help hold it open and/or drill some cross holes in the solid metal tube portion that is inside the sock):
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That's how I fixed mine :



Or you can use a jeep filter (this tip was provided by @Newman )




More details here https://www.ferrarichat.com/forum/threads/v-12-maintenance.307168/page-4#post-147684600 .