Ferrari Mailing List: Re: fuel gauge on 308

[francis newman (francis]

Great info Rick,

I will store that one away for future use - if needed.

Francis

On 21 Dec 2014, at 12:28, Rick Lindsay wrote:

> Regarding Ferrari gauges...
> 
> I have experienced only two kinds of gauge errors that were actually AT the 
> gauge; total failure and indicator sticking at the minimum position then 
> popping up when vibrated. The kind of error reported is almost certainly at 
> the sender.
> 
> Comments and tests, using the details provided:
> 
> 1. The fuel gauge in a 308 is a galvanometer. Basically, its a voltmeter. If 
> it goes to 'E' at rest, e.g. the ignition off, the internal mechanism has not 
> failed, the gauge is not the problem. (BTW, most British car gauges work by a 
> completely different principle.)
> 
> 2. It is very common for the sender to bind at some point. I have found this 
> to happen with an old car where condensation has caused corrosion on the 
> sender at a position where the arm long set. Witness my R-R's fuel level 
> sender.
> 
> 3. The senders is just a variable resistor. It is a coil of wire with a 
> contact that slides along the coil. Its position is set by a float on a stiff 
> wire arm. As the fuel level changes, the float position changes as does its 
> attached wire. Up gives low resistance, down gives high resistance. Ever 
> notice how the apparent fuel level changes when cornering? The float is going 
> up and down causing the resistance to change. 
> 
> 4. With the ignition on, unplug the harness wire from the sender. The gauge 
> should go to 'E'. If it does, the sender is your problem.
> 
> 5. Senders are typically easy to repair. At least they are in the cars that I 
> have owned. Just remove the retaining screws and manoeuvre the unit out. It 
> will be stuck pretty good at the gasket. Also, it has that long arm and float 
> attached so a bit of really careful twisting and turning is required.
> 
> 6. With the sender on the workbench,  slowly move the float through its full 
> range if motion. I suspect you will find that it binds in that lower 
> position. Clean the pivot and carefully clean the resistor. For the latter I 
> recommend only a blast of brake cleaner. Once smooth full range of motion is 
> achieved, oil the pivot and reinstall the sender.
> 
> 7. I don't know if new gaskets are available. I just cut my own from 
> parts-store bulk gasket material. Those shops also sell fuel-safe sealant. 
> Its a gasket dressing that is not attacked by fuel. That's what I use on the 
> gasket, to reseal the sender to the tank. Certainly don't want any fuel leaks 
> there to prove Clyde right! :-P
> 
> 8. You may find that the sender is held in place with a retainer ring rather 
> than screws. Procedure is the same except for attachment method. There's 
> probably a ground wire on the sender too, and a low fuel warning light 
> circuit. Just keep the wires and connectors on their correct positions and 
> the rest is pretty easy. A photo or three in advance aids with reassembly and 
> reconnection. 
> 
> 9. The 308 is more forgiving than say a Testarossa, with regard to parts 
> removal and replacement. I expect the sender can be removed with the tank in 
> place, but I can't guarantee that. When I rebuilt my Testarossa - as Clyde 
> can attest - everything has to be assembled in the correct order or that last 
> screw, bolt or nut can't be fitted! I learned this the hard way! I swear, at 
> times it felt like the radio knobs needed to be fitted before some of the FI 
> parts would go on! I bet I assembled that engine five times!
> 
> 10. So to summarize, remove the sender wire from the sender to see if the 
> gauge goes to 'E'. If so, the sender needs to be cleaned, repaired or 
> replaced. See above.
> 
> -rick
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