Quote:
Originally Posted by Brian
And I have a question too - sorry!
Running 36 fuel tank, original sender, original dash unit, 12 volt conversion, [alternator], runtz on gas gauge, another on oil pressure gauge.
Problem is that upon turning on ignition, needle in fuel gauge will climb and indicate [approximate] fuel level, but then when I start the engine and start driving, the needle goes down below empty and stays there.
Why would this be?
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A guess would be some type of wiring issue. You could start by checking the gauge with a "D" cell just to eliminate that. Grounding at the sending unit can be a problem, a jumper wire from the sender to a good known good ground would also be something to try.
Assuming the tank is indeed full and reads full with the ignition switch on, the gauge would be indicating maximum current flow through the gauge and sending unit (or some source to ground). If it drops when the engine starts something is reducing the current flow, as in an open circuit or grounding issue. Is there something somewhere that could move/change when the engine is running?
I would trouble shoot starting at the gauge. Connect a jumper wire to the sender post on the gauge. Once the engine is running and the gauge starts to move toward empty touch the jumper to a known good ground and see it the gauge starts to return to full (I would do this for only a short period of time). If it does the problem is not the gauge.
I would next connect a jumper to the sender unit connection (at the sender unit) and try it again. If the gauge stays on empty there may be a wiring problem between the gauge and the sender. If it moves back toward full in may be the sender itself or a ground issue.
To check between the sender being the issue and a poor ground, connect a jumper to a mounting bolt for the sender and try again. If the gauge stays on empty I would suspect the sender itself if it goes back to full it is most likely a sender grounding issue.