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Discussion Starter · #1 ·
I used this method to repair/r

I used this method to repair/replace the fuel sending unit on a 1979 carbed Boxer. I suspect it will work on an injected Boxer and probably on the 3X8 series Ferrari's.

The sympton: Fuel gauge reads zero and you just filled it up.

You need to decide if it is the gauge, the wiring or the sending unit. The easiest way to tell is to send +12V to the gauge through the wires from the sending unit to the fuel gauge. The fuel level sending unit is located on top of the passenger side tank. There are two leads coming from it plus a ground. One lead is for the level the other is for the red low reserve light.

Disconnect the two leads. Get a 12V battery, clamp the ground to the frame and take the positive to one of the two wires. You should be able to make the red light come on and the fuel gauge should peg full if the gauge and wiring are fine. If not, I would remove the gauge and take +12V to it directly to determine if it is the wiring/fuse or a faulty gauge. In my case I concluded it was the fuel level sending unit.

There are 6 nuts which retain the sending unit in the tank. Remove the nuts and carefully remove the sending unit. Be careful and stuff a rag in the open gas tank hole.

Examine the sending unit. There is a rheostat that the float attaches to. There is a "door" that can be removed from the rheostat to allow you to see the internals of the unit. It is fairly straight forward. One wire is connected to an arm that rides the windings of the rheostat and the other will connect to another arm that engages the red low fuel reserve light wiring. In my case the rheostat wiring had broken after 25 years of use.

I did not have any luck sourcing a new unit after calling the various Ferrari parts distributors. Ferrari UK does list it as available but after converting to dollars, paying VAT and shipping it was just under $400. Ugh!

However David Feinberg suggested I use one from a Fiat. He directed me to International Auto Parts . The one that I purchased was for a 2000 Spider, 1890-on, inj (Item no. 34285); $38.95, now we're talkin. The only problem is that the arm that attaches to the float is too short.

I spent considerable time making sure attaching the old float arm to the new sender would result in the same correct length from top to bottom. It was remarkable close, and certainly reasonable given the accuracy of the fuel gauge itself.

There is some modification required. First remove the old rheostat from the old fuel sending unit. Now remove the arm. Unfortunately, the contacts on the old, longer arm are designed differently than the newer one. What you want to do is to put the contacts from the newer arm onto the old, longer arm.

Get out the dermel tool. Carefully remove the contact body that is sodered to the old arm. This is hard to describe but I guarantee that once you look at the two arms you will see what has to be done. Now remove the new contact piece from the new arm; it is just press fit.

Put the new contact piece on the old arm. Study the orientation so that the contact arms are in line with the line of the float arm. It takes a bit of trial and error to get this to aling but it's not that bad. Soder the contacts in place. Again this is easier once you see what has to be done. You will also have to cut off a few mm of the arm portion that enters the rheostat. Again, no big deal.

The problem that I had that was that, though the bolt hole pattern was the same the new unit is rotated about 30 degerees from the old sending unit bolt hole pattern. This made the float arm hit part of the baffel on the inside of the fuel tank. By bending the arm slightly, actually to remove the existing kink in it, it can be made to clear the baffel. Again once you are there doing this in person it will become apparent what has to be done without effecting the travel length of the arm.

There you have it. For $40 and 2 hours time you know how much fuel you have on board.

Please feel free to comment especially about the applicability to the 3X8 series.
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