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Received: with LISTAR (v0.128a; list small-list); Wed, 10 May 2000 19:00:29 -0400 (EDT)
Date: Wed, 10 May 2000 19:00:29 -0400 (EDT)
From: Ford Truck Enthusiasts List Server>
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Subject: small-list Digest V2000 #65
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small-list Digest Wed, 10 May 2000 Volume: 2000 Issue: 065

In This Issue:
Re: [Fuel gauge]


Date: 10 May 00 20:00:14 EDT
From: Tim Turner>
Subject: Re: [Fuel gauge]

"Chris Oostveen"> wrote:
> I know this has been covered before. How do I check to see what is causing
> my fuel gauge to not function at all (stays on empty).

Assuming you have a 12V test light handy disconnect the plug to the
sender/pump, turn the key on and probe for the circuit that DIMLY lights the
test light. (In the wiring harness from the body.) This will be the 'feed'
from the guage; now run the test light from that pin to the corresponding
terminal on the sending unit and observe the guage, it should now be reading
something. (The exact value the guage reads will depend on the resistance of
your test light.)

Here's what you've done if all that happens:

1) Verified that the voltage regulator for the guages works (The dim light.)

2) The wiring between the sender and the guage is intact.

3) The guage works to some extent.

A safe bet that the sender is bad if all this test passes... If NOT then the
part that didn't happen will be a clue.

1) No dim light at the sender:
a) check the ground of your test light! :-)
b) bad CVR, but ONLY if temp & oil guages inop also
c) open circuit (bad wiring) between the guage and the sender

2) Dim light but no change in the guage when jumped to the sender:
a) bad guage
b) bad ground to the tank
c) bad printed circuit board/connection behind the inst. cluster

Alternatively if you KNOW which wire of the connector is for the sender then
temporarily jump it to ground to see if the guage goes to beyond Full with the
key on. Do NOT jump the wrong wire in the connector this way as you'll blow
the fuel pump fuse at a minimum!

It is an '88 2wd with
> the 2.0, 5 speed. Am I looking for dead circuits or dead sending unit?

Usually dead sending unit. The CVR (constant voltage regulator) supplies a
constant voltage (8v?) to the guages which then gets modified by the varying
resistance of the senders to ground. Ford & Chrysler have low resistance for
Full and high resistance for Empty so any break in the circuit causes the
constant 'E'. (GM works backwards; they go to Full when disconnected.)

Hope this helps!


PS: If you do need to change the sender it might be easier to unbolt the bed
and slide it back rather than dropping the tank if it's the low rider truck.

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