Hans Neureiter wrote:
Correct by saying these functions are semi separate. My original gauge
worked good, but the reserve light did not at all.
Than I installed a new sending unit. Here the reserve light works, but the
gauge is way off. Don't know why at this point (maybe it doesn't have that
4.7 ohm resistor in parallel like the old one has).
I tinkered with the old sender that was coated with algae and found a way to
clean it without braking the fine resistor wires. I plan on re-installing it
and see what's up with the new one.
Here is how it works:
The float has two contacts on opposite ends of its circumference that slide
up and down two resistor wires, making the combined length of the wire
greater as it descends, thus increasing resistance in the gauge circuit.
The reserve functions due to a brass disk at the bottom of the float
that bridges two fixed contacts at the empty position, completing a separate
circuit for the light. The reserve light has a second circuit that
illuminates the lamp at a lower intensity when turning on the key and gets
cancelled on start (self test).
The system works only properly if these contacts and the wires are clean.
On 1/21/06, Tim C <[EMAIL PROTECTED]> wrote:
Huh, this appears to be saying that the reserve light and fuel gauge are
independent of each other?
--
Hans. Not sure if you noticed, but the different senders
(123/126/wagon/gasoline/diesel/early/late versions) have a little or a
lot of different resistance values at full and at empty. I'm NOT sure
just how many different assemblies are involved or but the clearly are
some differences (it's clear that the plug for the T wagon sender
includes a resistor to compensate for the different tank shape/size). In
addition, early (manufactured before 9/82) senders do NOT have the
resistor and diode that permit the reserve light to be illuminated (as a
test) when the ignition key is on, but before the engine starts.
All of the senders in my 201 sedans (except one) read very accurately
(3/4 after 3.75 gallons are gone, 1/2 after 7.5 gallons are gone). The
one oddball was a recycled sender (may have come from a gasoline car or
may have been damaged in some way) and it drops MUCH faster. The reserve
light comes on PRECISELY when it should (1.85 gallons remaining)
suggesting that the resistance value of the sender is incorrect rather
than the float being out of calibration. I have NOT measured the
resistance as it's NOT critical - I can live with it reading a 15-20%
pessimistically as long as the reserve light illuminates 50+ miles
before I'm going to run out of fuel.
Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" [EMAIL PROTECTED]
'87 300TD 182Kmi, '84 190D 2.2 229Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5
turbo 237kmi
