Barney
I had a chance today to try some of your suggestions. I am not sure if
I am using the multi-meter correctly. Here is what I tried.
I know the tank currently has about three gallons in it. I haven't removed
the sending unit yet. I checked the tank grounding by taking a test light
and touching the sending unit wire stud with the ignition on and touching
the light probe to the tank. It is grounded.
I touched the sending unit wire from the gauge to the chassis and the
gauge went to full ( not to empty).
I wasn't sure how to connect the multi-meter so I tried a number of
different combinations. Grounded one end of the multi-meter to the
chassis and touched the other end to the electric stud on the sending
unit. With the ignition off and the gauge wire off I got a reading of 90.5
Grounded one end of the multi-meter to the chassis and touched the
wire to the gauge while it was disconnected . With the ignition off I
got 63.8.
Connected the sending unit wire and touched the multi-meter to the
electric stud and grounded to the chassis. With the ignition off I got
34.5
Are any of these what you were suggesting? Should I get the 0-70
with the ignition on, wire connected and ground the other end of the
multi-meter?
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> From: Barney Gaylord <barneymg@ntsource.com>
> To: Steven R Schultz <SSchultz@worldnet.att.net>
> Cc: mgs@autox.team.net
> Subject: Re: MGA gas gauge?
> Date: Sunday, October 04, 1998 11:31 PM
>
> At 07:45 PM 10/4/98 -0400, Steven R Schultz wrote:
> >.... '61 MGA gas gauge .... The wire is OK. With the car running the
> gauge usually reads from half full to three quarters full. When the wire
> is disconnected from the sending unit and ground the gauge goes to full
> which I am told indicates that everything is OK. All of the above would
> suggest that the sending unit in the gas tank is the culprit.
> >
> >How do I test the sending unit without taking it out of the car? Can I
> use a multi-meter to test it when the talk is full and again when it is
> close to empty?
>
> Check with an ohm meter. The sending unit should read 70 ohms to ground
> when the tank is full, and 0 ohms to ground when the tank is empty. So
if
> you ground the sender wire at the tank the gauge should go to the Empty
> mark. If you have a bad earth connection for the fuel tank the gauge
will
> not go all the way to the Empty mark.
>
> The tank is mounted in rubber insulated metal straps, and the filler pipe
> is connected with a large rubber hose. Original setup allowed for the
> sender to find ground through the metal pipes on the fuel pump. If the
> fuel pump is currently hooked up with small rubber hoses, there's a very
> good chance the tank is not grounded. Best solution is to run a ground
> wire from one of the mounting screws of the sender unit to the grounding
> lug on the frame which is about six inches away from it. If that doesn't
> solve the problem, the sender unit would be bad.
>
> >If I take it out of the car how do I test it? Can I ground it and move
the
> float up and down while attached to the sending unit wire and gauge?
>
> Yes, but you have to have power to the gauge, and the housing of the
gauge
> itself also has to be grounded. By itself, the sender should be 70 ohms
> with the arm full up and 0 ohms with arm full down, and a continuous
smooth
> transition of resistance through the full travel in between.
>
> >Should I try to fix it myself, send it to a specialist to fix it or
should
> I buy a new one from one of the Mail order houses?
>
> Check the resistance of the ground connection at the sender first, from
the
> tank to the frame, and add a ground wire if necessary. Then measure the
> resistance of the sender unit. If it doesn't transition smoothly from 0
to
> 70 ohms, then you need a new sender unit. I'd bet on the ground
connection
> being bad. These things are pretty reliable. Mine's 40 years old and
> still working fine.
>
> >When I reinstall it should I use Permitted?
>
> I had the sender unit out of mine to clean and paint the tank 20 years
ago.
> I put it back together with a THICK paper gasket, no sealant, and no
leak.
> just had it out again a couple months ago to measure the resistance, put
> it back in with the SAME old paper gasket, still no sealant, and still no
> leak. If you do need to use a sealant, be sure it is a type that is
> specified for use with gasoline. Read the container, don't guess.
>
> Barney Gaylord
> 1958 MGA with an attitude
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