Fuel guage problem

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schil123
Posts: 14
Joined: Wed Sep 28, 2016 5:23 am
Location: East Grand Rapids, MI

Fuel guage problem

Post by schil123 » Thu Jun 21, 2018 7:54 pm

Hello,

I replaced my fuel sending unit after pulling my fuel tank to clean it out. It was rusty and useless(sending unit). I made a good ground from sending unit right to the engine block. Still the fuel guage does not read anything besides empty. Figured it might be the ground at the fuel guage. So I pulled the ground wire and the fuel guage went straight to FULL. I am now assuming that the "hot wire" going to the sending unit is shorted to ground. Would this be correct. Anyone have any ideas. If this is the problem, what color wire is that wire at the guage? Should I run a new wire to the guage??

Thanks

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pcolette
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Location: Southwest Wisconsin

Re: Fuel guage problem

Post by pcolette » Thu Jun 21, 2018 8:25 pm

IIRC, the sensor wire from the sender to the gauge is “lilac”, or purple as we call it.
Paul C.
_________
'73 Swiss 710M
'89 Puch 230GE
2002 MB G500 (For Sale)

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Hotzenplotz
Austria
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Location: Vienna, Austria

Re: Fuel guage problem

Post by Hotzenplotz » Fri Jun 22, 2018 4:01 am

try to touch a well connected ground point with that wire to the sender.
if your gauge starts flickering, you identified the right cable ...
Cheers
Albert
========================
My Pinz has NEVER been with any army

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rmel
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Re: Fuel guage problem

Post by rmel » Fri Jun 22, 2018 9:43 am

What you are describing may be a bad meter.

If I read your description right, you removed the ground off the meter
then the meter pegged to Full. On most of the analog VDO gauges is
an internal voltage regulator the produces a constant voltage from the 24V
supply which then is used to drive one side of a wire-wound bi-metal strip,
the other end of that coil is connected to the Sender terminal. The Sender
completes that circuit providing current through the coil then move the needle.
If working properly, with a FULL tank, the sender is about 10 Ohms (float at top)
with a the maximum amount of current through the coil and thus a "full" reading.
On an empty tank the sender is in the ballpark of 180 ohms and a reading of "R".
By pulling the ground at the meter it is likely disabling the internal voltage
regulator piping a full 24V into that coil and thus a "Full" reading. That's a clue
the meter may be toast, likley the internal regulator has gone bad with no output.

You can try a couple of tests to verify that.
Get yourself a 100 Ohm resistor from Fry's or local electronics store.

Reconnect the Gauges Ground and 24V.
Remove the sender connection from the gauge.
Bridge the resistor across the "S" and Ground terminals of the Gauge.
If working properly it should read about 1/2 full (approximately).

This test eliminates the dependence on the Sender and it's ground, so
your just testing the Gauge. It's also a good idea get a Ohm meter reading
of the Sender, having a rough idea how much gas you have in the tank,
full is about 10 Ohms and empty is about 180. I'm betting your sender
is good -- but....verify that.
Last edited by rmel on Fri Jun 22, 2018 12:30 pm, edited 1 time in total.
Puller: 710K 2.7L EFI
Follower: Sankey MK 3, 3/4 Tonne
Driver: Ron // KO0Q

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pcolette
United States of America
Posts: 1356
Joined: Sun Dec 10, 2006 7:38 pm
Location: Southwest Wisconsin

Re: Fuel guage problem

Post by pcolette » Fri Jun 22, 2018 9:51 am

Here is an additional article which may be of some help:
Fuel Gaugeproblems.pdf
(79.1 KiB) Downloaded 24 times
Paul C.
_________
'73 Swiss 710M
'89 Puch 230GE
2002 MB G500 (For Sale)

schil123
Posts: 14
Joined: Wed Sep 28, 2016 5:23 am
Location: East Grand Rapids, MI

Re: Fuel guage problem

Post by schil123 » Sat Jun 23, 2018 11:12 am

@ Rmel

What you are saying makes total sense to me! I went as far as to run test leeds from the sending unit to guage and a ground from the sending unit to the guage. I still have the same issues. The sending unit is brand new. I have received new bad parts before, but I think you have hit the nail on the head. A new guage is cheap enough.

Thank you ALL for your input. Will follow up once I try the new guage.

Chad

schil123
Posts: 14
Joined: Wed Sep 28, 2016 5:23 am
Location: East Grand Rapids, MI

Re: Fuel guage problem

Post by schil123 » Wed Jun 27, 2018 8:04 pm

rmel wrote:
Fri Jun 22, 2018 9:43 am
What you are describing may be a bad meter.

If I read your description right, you removed the ground off the meter
then the meter pegged to Full. On most of the analog VDO gauges is
an internal voltage regulator the produces a constant voltage from the 24V
supply which then is used to drive one side of a wire-wound bi-metal strip,
the other end of that coil is connected to the Sender terminal. The Sender
completes that circuit providing current through the coil then move the needle.
If working properly, with a FULL tank, the sender is about 10 Ohms (float at top)
with a the maximum amount of current through the coil and thus a "full" reading.
On an empty tank the sender is in the ballpark of 180 ohms and a reading of "R".
By pulling the ground at the meter it is likely disabling the internal voltage
regulator piping a full 24V into that coil and thus a "Full" reading. That's a clue
the meter may be toast, likley the internal regulator has gone bad with no output.

You can try a couple of tests to verify that.
Get yourself a 100 Ohm resistor from Fry's or local electronics store.

Reconnect the Gauges Ground and 24V.
Remove the sender connection from the gauge.
Bridge the resistor across the "S" and Ground terminals of the Gauge.
If working properly it should read about 1/2 full (approximately).

This test eliminates the dependence on the Sender and it's ground, so
your just testing the Gauge. It's also a good idea get a Ohm meter reading
of the Sender, having a rough idea how much gas you have in the tank,
full is about 10 Ohms and empty is about 180. I'm betting your sender
is good -- but....verify that.

Rmel,

Thank you for your wise insight! The gauge was my problem. Installed a new one from SAV tonight. Now I just need to empty the tank and set the correct level.

Thank you

Chad

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rmel
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Re: Fuel guage problem

Post by rmel » Wed Jun 27, 2018 9:26 pm

Good, glad to hear that. Nothing worse that not knowing your gonna have an empty tank on the trail :P

ron
Puller: 710K 2.7L EFI
Follower: Sankey MK 3, 3/4 Tonne
Driver: Ron // KO0Q

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