Hi John
Your inquiry most ironic, as I just came in from solving a similar
challenge with my fuel sending unit, only with the reverse problem that
you have. This goes back to before my restoration, when the gauge would
only read, when the tank was full, between 1/2 and 3/4 on the gauge. I
traced the problem first to the voltage stabilizer. Lately- the gauge
has only been reading at the 3/4 mark when the tank was 'topped' or I
pulled the sending unit float up to the top with a coat hanger. I did
have resistor continuity throughout the travel range. To test this,
slowly raise and lower the float arm wire.
To Test your gauge and thus the wiring to it,first take the two wire
leads, the green one with the black stripe, and the blackground wire
and connect them together. This will give you an accurate zero
resistance and the gauge should read full or even better to the 2 dots
above the gauge's F line. When my gauge read correctly with this test, I
bought a new sending unit from MOSS. So a couple weeks ago I put the new
sending unit in. I tested it first and it gave an 'F' reaing when at the
'top stop' However, I put it in the tank and it still read only 3/4 when
I pulled the float up to the top of the tank with the coat hanger.
So today I got the old unit-hooked it up outside the tank and it would
only give 3/4 reading. I took off the two screws on the cover plate and
looked at the resistor and the 'wipe' contact. Looking very carefully
at the resistor- and the position of the 'wipe' at the top position,
there were still 4 or 5 thin winding s left in the 'circuit'. I
carefully bent the wipe to contact the very bottom of the resistor
(eliminating the last 4 windings) I then tested the unit and fould that
by tweeking the contact I could get the gauge to fead Full.
Then I pulled the 'new MOSS unit' from the tank. I took this apart.
While constructed differently- the windings are more graduated (start
small get wider at the top-maximum resistance),correct for the E gauge
reading), I did the same thing- eliminated the bottom few windings to
ensure no resistance at the full position. Cover still off, eventually I
got the new unit to 'send' the correct zero resitance= Full on the
gauge. I put the cover back on, and placed the sender in the tank and
duct taped in for testing. 'Coat hanger up' The 'up stop tab' limited
the reading to 15/16 Full. Removed the unit, and very gently I bent the
stop tab slightly to allow the float arm to make the 'zero' contact
inside, and after two adjustments - The gauge now reads at the Full
dots.
However, I then noted that once returned in the tank- the float, when it
hit the top of the fuel tank (coat hanger test method) was giving only a
7/8 indicator reading. So I took the unit out again and bent the float
arm slightly to make sure that when the float actually is 'peaked'-the
arm wire will be at maximum range at the stop and thus making sure the
internal connections in the sending unit will also be at zero resistance.
I have yet to determine if the gauge will be accurate thru the range.
In summary there are three adjustments:
-the internal connections at the windings
-the actual 'wipe' on the resistor throught he range
(make sure the 'wipe' is making contact, also make sure it is not
'scraping the windings- or this could lead to a 'break'. A break would
give an 'upper reading' as you reported. Full resistance could give an
'E' reading- or the needle might actually disappear at the lower end.
-the arm might need adjustment. However- if the arm is 'twisted' the
'wipe' can also disconnect in the sending unit.
Also check the LUCAR connections at the sending unit-make sure these are
tight on the gauge prongs, otherwise you'll get an intermmittent or
'non' circuit.
Let us know what you find.
Also for those who may face this someday, I did not have to remove the
tank, or break the fuel line at the tank fitting to access the sending
unit. I removed the (Chrome)Deck Filler Cap (loosen the band clamp under
the rear deck above the tank); the top two and two side tank
retaining/securing bolts, and loosened the bottom two bolts almost out.
This lets the tank drop about 3/8" and allows one to 'pull' the tank
topward the trunk. Then with an L screwdriver, I was able to remove the
6 tank sending unit retaining screws. Carefully one can manipulate the
fuel sender unit out of the tank - gently, very gently- don't want to
bend or twist the wire arm where in is attached to the sending unit.
Sherman
Sherman D. Taffel
Columbia MD
TR4 CT40054L 'The Toy'
Now with a much better working fuel indicator gauge.
- -----Original Message-----
From: John Edwin Pike [mailto:toadhall@pnc.com.au]
Sent: Monday, December 11, 2000 5:36 PM
To: Triumph Digest
Subject: TR3A Electrical Problem - Fuel Gauge
Gentlefolk,
I am returning to this list after a longish absence, and have a query for
your
combined minds.
The fuel gauge in my 3A reads "full" until I've used around 3/4 of the tank.
The needle then comes off the stops, and acts as though the total capacity
is
around 3 gallons. That is, when there's about 1 1/2 gallons left the gauge
indicates "half", and when the tank is empty that's what the gauge reads.
Being somewhat electrically challenged, my trouble-shooting to date has been
to remove the sender unit, clean the contacts on the resistor, and clean the
various earth contacts. None of this has made any difference.
Problem: How do I convince the gauge that the tank capacity is actually 12
gallons? And do I have a problem with the gauge, the sender or the wiring
in
between ??
Any assistance will be greatly appreciated.
John Pike
TR3A TS 75053 O
Australia
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