Dear Sharksters:
A few days ago, I asked the list for help with a gas gauge that does not
register immediately on start-up and after 15 minutes or so of driving,
points to full, regardless of the amount of gas in the tank. The sending
unit is new. I asked for a personal intercession with the Porsche gods from
anyone knowledgeable enough or with good connections for help in diagnosis.
I suggested that perhaps the pod has to come out to clean the connections
to the flex strip or else the gauge itself is shot or the continuity
between the gas gauge and the flex strip interface is interrupted. I have
no idea whether my suppositions are correct or not. In any event, no one
responded other than someone wanting to give advice about the voltage
readings; slightly off the mark. Surely this query should attract a
response, given the bandwidth evident on more trivial threads from time to
time. TIA.
gpsigal - 82 with nothing special
=================
Gerald P. Sigal" wrote:
A few days ago, I asked the list for help with a gas gauge that does not register immediately on start-up and after 15 minutes or so of driving, points to full, regardless of the amount of gas in the tank. The sending unit is new.
Gerald,
-----
I was hoping someone more familiar with gas tanks and gauges
would have answered your original question...
I just finished fixing a faulty gas gauge reading in my S4
last weekend. In my case, the in-tank sender unit was bad.
In your case, the problem sounds electrical. That said,
I did notice something I had never heard about before while
fixing my sender that may be worth looking at. The bottom of
the sender unit sits in a circular container (which actually
contains spiral walls within) that is fixed to the bottom of
the tank; the container is centered over the in-tank
fuel filter screen. When I pulled out my sender unit, I noticed
that the "lid" to this container was not attached to the side
walls. My guess is that the whole contraption exists to make
sure the gas is not in a turbulent state when it is pumped out
of the tank, but I do wonder if it may also play a role in
an accurate reading on the fuel gauge. It may be worth verifying
that all of these pieces were reinstalled properly when the
sender unit was replaced.
--
Jim Stadter
=============
Here is a procedure to test the fuel gauge system. I
assume no one replied
since you did not do the normal check out to help isolate the problem.
(Although I thought I sent some e-mail to someone about trouble shooting the
tank unit) Unless it is a known gremlin that has a magic fix then you
really have to start at the beginning and work backwards until you locate
the problem.
A pegged gauge can generally be traced to a short in the system.
1. Locate the sending unit in the tank. It is under the carpet in the rear
of the car opposite the spare. There is a black plastic cover, often under
a white piece of fireproof insulating material, that can be pried up.
2. Remove the wire plug attached to the unit. If the gauge returns to
empty
then the problem is in the sending unit - an internal short in the wiring of
the unit itself.
3. If the gauge is still pegged, then the problem is in either the wiring or
the gauge.
4. Disconnect the wiring harness at the pod. This will make the gauge go
to
empty along with everything else.
5. Find the sending wire on the sending unit. There is a wire from the
gauge and a ground. There is also a wire for the fuel light. Check
the
wire to the unit with an Ohm Meter. If it is a dead short to ground then
there is a short in the wiring. Somewhere the wiring harness has chafed
and
is contacting the chassis. This may take a little driving to make the
contact as the insulating is just getting worn off and may even need a
little heat to make a ground contact. Remember on German cars Brown is
Ground.
6. If there is no short in the wiring then the problem is with the pod. To
fix this you will have to pull the pod. The most likely case will be a bad
circuit board on the back of the pod or the gauge itself. The pod
connections can be cleaned up with an eraser and this may be all it takes -
but with an 82 I would not count on it. You can test the gauge separately
by rigging up some wiring to the tank unit, but you have to be careful. If
the gauge unit tests out good then the circuit board has some bad
connections.
My best guess - you have some corrosion on the connection to the gauge.
DEVEK has replacement pod circuit boards - doing this is worth the effort.
I think have a gas gauge laying around some place if you need one.
Hope this helps.
Dan B.