From: ghoneycutt@charter.net
Sent: Friday, July 19, 2002 1:21 PM
To: 928
Subject: [928] Re: Fix a fuel gauge on an 84S?

Mark,

I'm basing this on my 86 model.

Possibilities-
Gauge or gauge circuit connection
Sending unit
fuel tank vent tube pinch allowing only a 3/4 fule fill-up at pumps.

There are three wires at the fuel sender connection in the rear of the
car. Look under the rear carpet, there is a shield and a plastic round
cover. Once removed, you will see the 3 wire connector for the sender. The
sender has a resistance of roughly 74 ohms to ground when the fuel level
is empty and roughly 0-2 ohms to ground when the tank is full. To check
your gauge, pull the connector off the sender, jump the ground wire
(brown) to the violet striped wire. Turn on accessories with the key (you
don't need to start the car). By jumping those wires, you are sending a
close to 0 ohm signal to the gauge. It should read full. If it does, your
gauge circuit is probably OK and you may need to look into the possibility
of a pinched air relief hose for the tank and the possibility that you are
only getting 3/4 of fuel into the car. (I drained my tank when replacing
the fuel filter put 5gal in at home and 16.7 in at the pumps. This
verified that my tank is capable of holding capacity, my problem is
somewhere else, not a pinched hose).

Or a bad sending unit. Fill the car at the pumps, pull the connector and
check the resistance on the pins which fit brown and violet wires at the
sending unit, should be close to 0 ohms when the tank is full.

Or, your problem may be the gauge, harness connectors to the instruments,
ground to the steering column area, or interconnect from the sending plug
through the central (fuse) board to the dash harness). I can only get 7/8
full off my gauge with the wires jumped. I loose about 1 ohm resistsnce
from the sending plug to the dash harness. I measure about 2 ohms at the
instrument harness plug.

I cleaned the edge connectors on the instrument foil where the harness
plugs fit. I gained about 1/2 needle width towards full by doing that.
Also, my temp guage reads about 1/2 needle width hotter (closer to
reality) than before I cleaned the contacts.

Greg





-----Original Message-----
From: Chris Ford [mailto:Chris.Ford@worldwidepackets.com]
Sent: Monday, December 16, 2002 11:45 AM
To: 928
Subject: [928] RE: Check guages


Not sure what you are trying to acheive with the temp gauge but back to
the fuel gauge ..

Go to the fuel sender wiring in the hatch area, its on the right side under
a thin metal sheet. Pull the connector, then ground the sensor wire, offhand
I don't remember the color but refer to the wiring diagrams as it is probably
different for your year anyway. I seem to remember there are 3 wires, ground,
fuel gauge and low fuel light warning.

If on grounding (the correct wire) the gauge reads 3/4 (or not full) there is
an issue in the upstream wiring, if it reads full then there is likely an issue
with your fuel sender unit or the breather pipe from the tank may be blocked
which would mean you can't fill the tank all the way.

If its the wiring next place to look is the pod, (remove pod) clean all those
connection on the back, an eraser works well enough. On the PCB at the back 
of the pod there are small nuts for the 4 small gauges which hold in a connector.
Clean these too. Retest gauge as before. If it now reads full your done.

If not remove the fuel gauge from the pod, you'll find a 100R resistor at the
back, wattage of this resistor appears marginal, remove one end of resistor 
and check resistance with a digital meter. Replace if reading is incorrect.

Of course if at the end of this it still does not read full .... its likely the gauge.

Hope this helps

Chris



From: Glen Larson [mailto:bigdadglen@earthlink.net]
Sent: Wednesday, June 04, 2003 1:00 AM
To: 928
Subject: [928] Fixed fuel gauge



There was some interest expressed in this exercise, so here goes...

Being exposed to gas, some coating and corrosion is inevitable in the 
sender which was the culprit.

There are three connections: one for the empty signal (yellow), one for 
level (purple) and one for ground (brown). The ground runs to behind the 
right interior quarter panel. The empty signal should have 12 volts. The 
level signal has about 3.25 volts.

All combinations of connections were "open" so...

I removed and disassembled the sender. I found that the feed-throughs 
for the level and empty signals were corroded and no signals were 
passing from the cap to the actual sensors. This was fixed by soldering 
short pieces of wire from the protruding rivet to the "tangs." The wire 
on the empty feed-through fell off, but the heat and solder made it 
work. (For a time.)

The operation of the sender is fairly simple. There is a float running 
on a shaft. At the bottom, it shorts the empty terminal to the ground 
terminal.

The level is measured using a piece of resistant wire that runs in a 
"U." The ends of the wire are connected to the ground and level 
terminals. The float has contacts to both sides of the "U" so the 
resistance varies as the float moves. At the top, the resistance will be 
low, around 3 ohms. At the bottom, the resistance will be around 76 
ohms. As the wire connects the terminals, if the float is not contacting 
the wires, the resistance will be near 80 ohms.

After the R&R, I reinstalled the sender, but the gauge didn't work well. 
Occasionally, it would flick up especially when hitting bumps, so that 
was progress.

This suggested the gauge itself and the wiring. I picked up an extra 
gauge and compared it to the one in the pod. Both should similar 
resistances, which I forget, so I put the old one back in.

Looking at the wiring diagrams, the signal runs from gauge to the fuse 
panel on H3 and on to the sender from T3. "H3" means the 8th connector 
from the left (A,B,C,D...) along the bottom of the panel and the third 
signal from the top on that connector, starting in the upper left 
corner. The lower part of the cover needs to be removed to see these. 
Note that the odd-ball feeds in the middle are not part of the 
left-to-right counting, but have letters molded into the plastic. You 
can also see some letters at the very bottom of the panel.

Both H3 and T3 showed 3.25 volts and the purple wire at the sender 
showed 3.22. A bit of loss, I figure.

Removing the connector and probing the terminals showed that the sender 
was not working right, again. The ground was good, and the voltages were 
right (12 and 3.22) on the connectors.

With the engine off and the connector on the sender, the resistance 
between the ground terminal and the level terminal was around 32 ohms. 
Sounded good. Except that, with the connector removed, the resistance 
between ground and the level terminal was 53 ohms. Checking the 
terminals, connector removed, showed around 80 ohms from level sense to 
ground. The sender was hosed, again. (53 in parallel with 80 gives 32, 
abouts)

Removed the sender and checked it out. On the bench, the resistances 
once again looked right. I got some lacquer thinner and cleaned the 
wires and sliders on the float. I also used some 400 grit sand paper on 
the wires. (Carefully) Looking at the float, I noticed that on one side 
the wire didn't run through the contact fingers right. I used the 
sandpaper to brighten the fingers (carefully) and slipped the wires back 
into position.

I also soldered in a couple of stands of wire across the rivet and tang 
of the empty signal. Stuck this time.

Put it back in, and tried it...Yes. The gauge worked! (For the first 
time in the two years I've had it!)

Glen
'80 Euro S - Getting down the list