Fuel Return Line

[jasonb]

Am I correct in understanding that an FI fuel pump system should return unused fuel to the tank?
Is it true that the newer Mexican beetle FI pump system returns fuel to the pump instead?

I am concerned about buying a new gas tank for the FI system that I am planning. I had thought that since new (btlmex) gas tanks are set up for fuel injection that they would have a fuel return line to the tank.

Miguel at Btlmex informs me that the return line goes to the pump. Is this a change from the earlier acvw FI systems?

[TomB]

FI systems control fuel pressure with a bypass valve that maintains pressure by returning excess flow back "upstream." Historically this has been back to the tank. The Mexican Type1 injection system uses a special Pierberg pump mounted on a bracket on the right framehead under the tank, with a single line from the tank to the pump. There are still two 7mm lines running through the tunnel to the engine, but the return fuel goes to a return fitting on the special pump instead of back to the tank. If a lot of fuel were being recirculated, in theory this could heat the fuel and potentially cause cavitation at the pump inlet, but in this system that isn't a problem. With the pump location any air bubbles can still work their way back up to the tank when the pump isn't drawing too much from it.
The Mexican system was not derived from the 70s US Beetle system (which was never made in Mexico), but was a change from their carburated production to have as little impact on production and retrofit of cars as possible. Thus it uses the same single-outlet tank, and at the engine uses the same heater boxes, but feeding a new cat/muffler combination that can replace the standard muffler on retrofits. (The retrofit was to allow cleaning up the Taxi population in Mexico City with cleaner FI/Cat systems.) The engineering is really pretty good.
I have two cars from Miguel which are our main transportation, and the system works very well.
I see no problem using the same pump and return system with other FI units, as long as the capacity and pressure needs are similar. Btlmex sells the pump also, but the mounting bracket is normally part of the chassis - but it wouldn't be hard to make one.

[jasonb]

So in theory you might recommend using this pump system as an alternative to tapping the gas tank for a return line? At least in a mild engine like my stock 1776.

Have you ever experienced any hard starts on a hot restart as a result of overheated fuel in the line?

Do you happen to know if the Btlmex gas tanks, which are supposedly FI ready, have the gas sump(don't know what else to call it) at the bottom of the tank for constant fuel flow?

Thanks for your help. You appear to be insanely well informed on this matter.

[TomB]

I've had no hot start or running problems, even in our 100F+ summers. I wouldn't hesitate to use the pump and tank setup on a 1776. I don't know the tank's details you refer to, but the general quality of the factory tank is better than any aftermarket I've seen.