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hi, I need some advice. can you guys tell me whats wrong with my speedometer, it is stuck on 30 mph. it won't go up or down. the car will not be running and it is stuck, even when it is running it is stuck. i hope its just the speedometer itself and not the cable. problem number two my gas tank guage always reads empty, what is wrong with it???
 

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I still think a new speedo is in order. What is the W #? As for the gas gauge it could be a bad wire somewhere or ground at the tank. Then again the float for the sending units stick or don't float anymore and cause this problem.
 

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To test your fuel gauge, take a 40ohm/2Watts resistor from an electronics shop, locate the wire going to the sender unit, disconnect it there, and put the resistor between the wire and a metal bolt (ground). Switch the ignition on, and the gauge should read full. If not you should investigate the dash gauge. If it does read full you should investigate the sender unit.
 

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I disagree: the fuel sender reads 3.3 Ohms FUll and 89 OHms empty. and is NOT linear (because the tank is not)

I posted the tank cal curve somewhere it shows ALL the Ohmic readings Vs. gallons for the entire sender range--very handy chart.

JJ
 

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DESTEC: I agree as well, it has struck me about 2 months ago, but since the FSM states the test to be so, shouldn't it give good results for testing?

I must confess I haven't tried it...
 

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When I check to see if the gauge is working I just remove the wire at the sending unit and ground it. If the gauge reads FULL then the problem is probably in the sending unit. No reaction at the gauge I make sure there is 12V to the gauge and then ground the terminal that the sending unit wire is attached to. It can quickly be determined whether the gauge is functioning, a break in the wire between the sending unit and the gauge, etc. My method doesn't test for correct functioning of the gauge but it is simple, quick and cheap.

HTH,
Harold
 

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Apparently the difference between FSM recommendation for testing (40 Ohms) and actual values (3.3), is that the impendance of a "dead" circuit is different than in a "live" one, due to the presence of current flow, and cannot be compared.

This is why you cannot test resistors while still in circuits, one end must be disconnected first...

And propably the FSM recommendation is just there to avoid a short circuit through the gauge...
 
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