fuel gauge pegged on full

fuel gauge pegged on full

i have a puzzle that i cannot figure out.  maybe because i dont know how to troubleshoot my fuel gauges.  i have a 1972 cessna 172L, the fuel gauges are paired with either the oil pressure gauge or oil temp gauge.

i recently had an over voltage which blew up the regulator and over voltage sensor, thus frying the transponder and navcom and assoicated CDI.  this occurred after a garmin 420 install.  i dont think the 420 install is the cause its, since the mechanics believe the alternator shielding wire <dont know what this is> broke and spiked the system. all has been fixed. my crazy luck.

when the master is turned on, the left fuel gauge works and goes to half tanks, the right gauge stays on Empty until i repeatadly tap on the face of the gauge and then jumps past Full <pegged>.  my memory is blank on when this problem started, i think after the voltage spike. morecrazy luck.  but i have a hard time thinking the spike would damage the gauge since its on a breaker. when the master is turned off, both gauges slowly go back to Empty.

so my puzzle is, how to i test the gauge before i have someone pull it and send it out for overhaul? 

how would i know if its the sending unit?  first i would have to find the sending unit. 

is the OHM range 30 - 240 for these gauges?  30 being full and around 100 being half tanksish?

on the back of the gauges, there are two wires.  i suppose one is to power and the other is to the sender unit.

thanks

kyle

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Re: fuel gauge pegged on full

Kyle
The fuel quantity transmitter is located under a small access panel in close proximity to the fuel tank filler cap (one on each wing). This panel should have three screws. To verify that the gage is good, remove the single wire at the transmitter,and with the master on, ground the wire. You should see the gage swing toward full. It would be safe to install a long jumper wire to the transmitter wire and ground it to a seat track as if there is a small spark it won't be a problem, additionally, you will be able to monitor the gage as well. Obviously there has been some work done under the panel, before going thru checking the transmitter I would check for loose wiring at the gages. You are correct on the wiring at the gage, one is power and one is from the sending unit...hope this helps some...
-Tom

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Re: fuel gauge pegged on full

we swapped the leads going to the fuel gauges.  putting the right fuel gauge wires on the left fuel gauge and voila, the sender in the right fuel tank works.  thus, it must be a bad fuel gauge. 

to send the unit out for repair, do we need to send the entire cluster <fuel gauge and oil temp> or do i need to just send the fuel gauge?

removing the oil temp line is simply unscrewing it correct?

thanks for the help.

kyle

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Re: fuel gauge pegged on full

If there is any chance that you may mess something up getting the gage out I would send the cluster, and identify what you want done. The oil line does unscrew from the gage, I think its 7/16", put a baggie with a tie rap on the end of the oil line or plug it with a line plug, otherwise you will have a mess to clean up.

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Re: fuel gauge pegged on full

while shopping around for a replacement gauge, part number 441346, cessna has a service kit SEB92-13 <for cessna 172s> that offers replacement gauges and transmitters as a set for around $260.00.  there are also service kits for cardinals and 210s.

well i am looking for a gauge, can anyone tell me if part number 441344 is an alternate number for 441346?  my parts manual has only 441346 listed.


thanks

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